STRAIN RATE EFFECTS ON TENSILE FRACTURE
AND DAMAGE TOLERANCE
OF COMPOSITE LAMINATES
by
Yew-Poh Mak
B.S. Aerospace Engineering, The University of Michigan (1990)
Submitted to the Department of Aeronautics and Astronautics in
Partial Fulfillment of the Requirements for the Degree of
MASTER OF SCIENCE
at the
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
June 1992
Copyright @Massachusetts Institute of Tech(o2gy, 1992. All rights reserved.
Signature of Author
DepE meri of Aeronautics and Astronautics
15, 1992
L
-May
Certified by
7
Professor Hugh L. McManus
A
Thesis Supervisor
Accepted by
Aert
MASSACHUSETS INTUTE
OF TWFHNflr.OGY
JUN 05 1992
(/'rotessor Harold Y. Wachman
Chairman, Department Graduate Committee
Strain Rate Effecta on Tensile Failure and
Damage Tolerance of Composite Laminates
by
Yew-Poh Mak
Submitted to the Department of Aeronautics and Astronautics on May 15,
1992, in partial fulfillment of the requirements for the Degree of
Master of Science.
ABSTRACT
An experimental study was carried out to investigate the behavior of
graphite/epoxy laminates under uniaxial tensile loading at strain rates
ranging from 0.0042 e/min to 2 e/min. The specimens were manufactured
using two methods: automated tow placement and manual tape layup.
The two material systems used were IM7/977-2 and AS4/938. The failure
strengths, failure modes and laminate properties of both unnotched and
notched specimens were measured. IM7/977-2 tape layup specimens were
insensitive to strain rates between 0.005 e/min and 0.5 e/min, except for
observed differences in the failure modes of the notched specimens.
Although the undamaged response of the AS4/938 specimens was not
dependent on manufacturing technique or strain rate, their damage
tolerance was dependent on both factors. Notched tow placed specimens
were stronger than notched tape layup specimens at all strain rates. The
failure strengths of the notched tape layup specimens were significantly
strain rate dependent, decreasing by about 20% at 2 e/min; the notched tow
placed specimens showed little strain rate sensitivity. The failure modes of
the notched tow placed and notched tape layup specimens differed, but were
independent of strain rates. The notched tow placed specimens exhibited a
progressive failure, surviving to loads well beyond the load at which
damage initiated at the notch tip. Conversely, the notched tape layup
specimens at high strain rates exhibited a brittle failure; they failed soon
after damage initiation.
Thesis Supervisor:
Hugh L. McManus
Title:
Boeing Assistant Professor, Department of
Aeronautics and Astronautics, Massachusetts
Institute of Technology
-2-
ACKNOWLEDGMENTS
The completion of this thesis is by no means an individual effort.
Professor Hugh McManus has provided immeasurable guidance and
patience throughout the conduct of this research. He is always available
and approachable for all the questions and doubts I have, or just to talk
about anything other than work. My gratitude also goes to Professor Paul
Lagace, for giving me the opportunity to work at TELAC, and Professors
John Dugundji and Michael Graves, for their concern and advise for my
work. Professor Anthony Waas deserves special mention for generating
my interest in composites.
Albert Supple taught me how to do things the way they are done in
the 'real' world. Thanks Al, for all your help and concern. My team of
UROPs deserves all the credit for expediting the experimental work and
helping to prepare this document. Thank you, Kimberly Kohlhepp, Amy
Gardner and Attila Lengyel, for all your help.
Matt Beaumont
programmed and debugged the data acquisition program and Narendra
Bhat answered all my little and big questions. Thank you! My colleagues at
TELAC have made going to work a little less boring. Thanks to all and
especially: Mary, Laura, Peter, Wilson, Ed and Hiroto.
Life at MIT would have been a painful experience if not for the dudes,
Jose (Pep) Ferrer, Mark (Camster) Campbell, and the rest of the gang:
Charrissa, Kathy, Dave, Norm, Eric (Strang'O), Len, Pete, and John. Also,
my two incredibly hilarious best friends, Scott (the armchair rocketscientist) Heifetz and Nitin (the rational romantic) Subhedar, have provided
tremendous encouragement all this while. Your long distance calls have
kept me in touch with sanity.
-3-
DEDICATION
This document is dedicated to my parents and family, whose love and
concern through all these years of separation, is very much appreciated.
You have provided me with the strength and purpose to move ahead,
especially in the worst of times.
4-
To the Powerful and the Wise:
Graduate School - it's a test of ultimate will
a heartbreak climb uphill
We're lost in a world of our own a world under anaesthetic subdivided and synthetic
Time becomes a spiraland space a curve
and though we might get dizzy
we try not to lose our nerve.
At the same time we're looking into
the eye of the storm
we try to maintain an air ofjoie de vivre
to improvise and orchestrate
illusions of careless flight
through our graduateschool years
We hope our wild kinetic dreams
will transport our desires
and drive us when we're down.
Every day we're standing in a wind tunnel
racing towards the future
We often wonder whether we're
in a groove and on a roll
or in a rut and on a slide
But we keep heading down those tracks
driven on without a moment to spend
on anything but our work.
Throughout our graduate school years
we physically punish our bodies
while our spiritsfly on dangerous missions
and our imaginationsare on fire
We'refocused high on soaring ambitions
consumed in a single desire
In the grip of a nameless possession
we are slaves to a driving obsession.
And finally it comes - graduation
As we examine our scarsof pleasure
and scars of pain
We realize that good work
is the key to good fortune
And then we receive our degree one moment's high and glory rolls on by
like a streak of lightning
thatflashes andfades in the summer sky
The moment may be brief
but it can be so bright.
We're only immortalfor a limited time...
RUSH, a compilation
N.S., 1992
-5-
FOR~EWORD
This investigation was conducted in the Technology Laboratory for
Advanced Composites (TELAC) of the Department of Aeronautics and
Astronautics at the Massachusetts Institute of Technology. This work was
sponsored by Boeing Commercial Airplane under Purchase Order Number
FZ-282568-0755N.
-6-
TABLE OF CONTENTS
Ea
Chanter
1
INTRODUCTION .................................................................. 17
2
BACKGROUND
22
.....................................
2.1 Fracture of Composite Laminates .................................
22....2
2.1.1 Unnotched Specimens............................................22
2.1.2 Notched Specimens.................................
...............
24
2.2 Strain Rate Effects on Composite Laminates.........................27
2.2.1 Strain Rate Effects on Composite Properties...............28
2.2.2 Strain Rate Effects on Composite Failure.......................31
2.3 Tape Layup and Tow Placement Manufacturing
Techniques...................................................................... 33
3
EXPERIMENTAL PROCEDURE ............................................... 37
3.1 Experimental Approach...................................................37
3.2 Material Specification and Fabrication .............................. 39
3.3 Preparation of Specimens for Testing....................46.......
3.3.1 Measurement of Coupons .......................................... 46
3.3.2 Measurement of Panels..........................................47
3.3.3 Attachment of Fiberglass End Tabs .............................. 50
3.3.4 M achining of Slits ....................................................
51
3.3.5 Attachment of Mounting Jigs for Panels ....................... 53
-7-
Chapter
Page
3.4 Instrumentation .............................................................. 57
3.4.1 Unnotched and Notched Coupons.................................57
3.4.2 Notched Panels .......................................................... 58
3.5 Testing Procedures..........................................................61
3.6 D ata Collection ................................................................ 62
3.7 Data Reduction ...........................................
4
RESULTS ...............................................
.........
66
.............
68
4.1 Expected Strain Rate versus Measured Strain Rate ............... 68
4.2 IM7/977-2 Test Results ..............
.....................................
4.2.1 Unnotched Coupon Results.......................................... 69
4.2.2 Notched Panel Results
............................
72
4.3 AS4/938 Tests Results ........................................................ 83
4.3.1 Unnotched Coupon Results........
...............................
4.3.2 Notched Specimen Results............................................
4.3.3 Strain Distribution of Notched Panels
93...
........................... 101
4.3.4 Mar-Lin Correlation of Notched Specimens ...................
5
83
107
DISCUSSION ........................................................................ 113
5.1 Strain Rate Effects on IM7/977-2 Specimens..........................113
5.1.1 Unnotched Coupons ....................................................
5.1.2 Notched Panels ..................
113
................................. 114
5.2 Strain Rate Effects on AS4/938 Specimens ............................ 119
5.2.1 Unnotched Coupons.................................................... 119
5.2.2 Notched Specimens .................................................. 122
e
Chapter
6
CONCLUSIONS AND RECOMMENDATIONS ..........................
131
6.1 Conclusions ............................................................
131
6.2 Recommendations...........................................................132
REFERENCES.......................................................................133
APPENDIX A..........................................................................139
APPENDIX B ........................................................................
143
APPENDIX C ..........................................................................
153
APPENDIX D ..........................................................................
165
APPENDIX E ..........................................................................
185
-9-
LISM OF FIGURES
Figure 2.1
Figure 2.1
Loading Regimes at Different Strain Rates........................29
Figure 2.2
Schematic of the Tow Placement Process ........................... 35
Figure 3.1
Tensile Coupon Configuration .......................................... 44
Figure 3.2
Tensile Panel Configuration........................................45
Figure 3.3
Schematic of Coupon Measurement Locations...........
Figure 3.4
Schematic of Panel Measurement Locations ...................... 49
Figure 3.5
Schematic Representation of a Slit. ................................... 52
Figure 3.6
Jig Plate Dimensions and Bolt Tightening Sequence. .......... 55
Figure 3.7
Side View of Panel Secured in Mounting Jig .....................
Figure 3.8
Strain Gage Placement for Unnotched and Notched
C oupons......................................................................... 59
48
56
Figure 3.910 Strain Gage Placement for Notched Panels ........................ 60
Figure 3.10 Photograph of tensile coupon in hydraulic grips prior
to testing........................................................................
64
Figure 3.11 Photograph of tensile panel in hydraulic grips prior
to testing .....................................................................
65
Figure 4.1
Average Failure Stress vs. Strain Rate for IM7/977-2
Specim ens ......................................................................
Figure 4.2
Sketches of Different Failure Modes. .............................. 73
Figure 4.3
Failure Modes of IM7/977-2 Unnotched Coupon and
AS4/938 Unnotched Coupon.................................74
Figure 4.4
Photograph of Failed IM7/977-2 Unnotched Coupon at
Different Strain Rates ................. .........
..................... 75
Figure 4.5
Stress-Strain Curves of IM7/977-2 Unnotched
Coupons at Different Strain Rates .................................. 76
Figure 4.6
Failure Modes of IM7/977-2 Notched Panels at
Different Strain Rates .......................................
............
-10-
71
79
Figure
Figure 4.7
Distribution of Failure Modes for IM7/977-2 Notched
P anels. .........................................................................
Figure 4.8
Photographs of Failed IM7/977-2 Notched Panel at (a)
0.005 e/min and (b) 0.025 e/min ........................................ 81
Figure 4.9
Photographs of Failed IM7/977-2 Notched Panel at (c)
0.1 e/min and (d) 0.5 e/min............................................... 82
.80
Figure 4.10 Average Failure Stress vs. Strain Rate for AS4/938
Tape Layup Specimens.................................................85
Figure 4.11 Average Failure Stress vs. Strain Rate for AS4/938
Tow Placed Specimens.....................................................86
Figure 4.12 Photograph of Failed AS4/938 Tape Layup Unnotched
Coupon at Different Strain Rates ....................................
88
Figure 4.13 Photograph of Failed AS4/938 Tow Placed Unnotched
Coupon at Different Strain Rates.......................................89
Figure 4.14 Stress-Strain Curves of AS4/938 Tape Layup
Unnotched Coupons at Different Strain Rates...................90
Figure 4.15 Stress-Strain Curves of AS4/938 Tow Placed
Unnotched Coupons at Different Strain Rates.................91
Figure 4.16 Failure Modes of AS4/938 Tape Layup and Tow
Placed Notched Specimens......................................95
Figure 4.17 Photograph of Typical Failed AS4/938 Tape Layup
and Tow Placed Notched Specimens ............................... 96
Figure 4.18 Photograph of Failed AS4/938 Tape Layup Notched
Coupon at Different Strain Rates.....................................97
Figure 4.19 Photograph of Failed AS4/938 Tape Layup Notched
Panel at Different Strain Rates. ........................................ 98
Figure 4.20 Photograph of Failed AS4/938 Tow Placed Notched
Coupon at Different Strain Rates.......................................9
Figure 4.21 Photograph of Failed AS4/938 Tow Placed Notched
Panel at Different Strain Rates. ........................................ 100
Figure 4.22 Average Strain Distribution of AS4/938 notched panel
at 0.0042 strain/min.............................................. 103
-11-
PFage
Figure
Figure 4.23 Average Strain Distribution of AS4/938 notched panel
at 0.1 strain/m in ........................................................... 104
Figure 4.24 Average Strain Distribution of AS4/938 notched panel
at 2 strain/m in ................... ......... ................................. 105
Figure 4.25 AS4/938 Notched Failure Stresses and Fracture
Prediction Curve at 0.0042 e/min ....................................... 10
Figure 4.26 Notched AS4/938 Specimens Failure Stresses and
Fracture Prediction Curve at 0.1 e/min ..........
...... 111
Figure 4.27 AS4/938 Notched Failure Stresses and Fracture
Prediction Curve at 2 e/min .........................................
12
Figure 5.1
Experimental and Predicted Stress-Strain Curves of
IM7/977-2 Unnotched Coupons. ........................................ 115
Figure 5.2
Strain Readings Collected of Typical IM7/977-2
N otched Panel............................................................... 116
Figure 5.3
Plot of Notch Tip Strain versus Normalized Time of
Representative IM7/977-2 Notched Specimens at
Different Strain Rates ........................................... ........ 117
Figure 5.4
Experimental and Predicted Stress-Strain Curves of
AS4/938 Unnotched Coupons .......................................... 121
Figure 5.5
Strain Readings Collected of Typical IM7/977-2
Notched Panel .............................................................. 124
Figure 5.6
Failure Initiation Stress and Final Failure Stress of
AS4/938 Notched Specimens, 19 mm Slit .......................... 125
Figure 5.7 Failure Initiation
Stress and Final Failure Stress of
AS4/938 Notched Specimens, 19 mm Slit...
.................... 126
Figure C.1-Figure C.12
Strain Distribution of AS4/938 Notched
Panels at Different Strain Rates ...................... 53-164
Figure D.1-Figure D.20
Collected Data of Tensile Tests conducted
on IM7/977-2 Specimens..............................165-184
Figure E.1-Figure E.90
Collected Data of Tensile Tests conducted
on AS4/938 Specimens .......................
-12-
185-274
LIST OF TABLES
Table
Table 3.1
Material and Calculated Laminate Properties....................40
Table 3.2
Test Matrix for Tensile IM7/977-2 Specimens ...................41
Table 3.3
Material and Calculated Laminate Properties................42
Table 3.4
Test Matrix for Tensile AS4/938 Specimens .......
Table 3.5
Stroke Rate Settings and Data Collection Frequencies
Used in Tensile Tests ....................................................... 63
Table 4.1
Average Failure Stress of IM7/977-2 Specimens at
Different Strain Rates ...................................................... 70
Table 4.2
IM7/977-2 Unnotched Coupon Stiffness Data at
Different Strain Rates .................................................... 77
Table 4.3
Average Failure Stress of AS4/938 Specimens at
Different Strain Rates ..............................................
.............
43
84
Table 4.4
AS4/938 Unnotched Coupon Stiffness Data at
Different Strain Rates..................................................... 9
Table 4.5
Average Mar-Lin Fracture Parameter (Hc) for
AS4/938 specimens at Different Strain Rates ...................... 109
Table 5.1
Average Stress at Failure Initiation and Ratio of
Initiation Stress to Failure Stress for the IM7/977-2,
51 mm Notched Specimens.........................................118
Table 5.2
Average Stress at Failure Initiation and Ratio of
Initiation Stress to Failure Stress for the AS4/938,
19 mm Notched Specimens ................................................. 127
Table 5.3
Average Stress at Failure Initiation and Ratio of
Initiation Stress to Failure Stress for the AS4/938,
51 mm Notched Specimens.............................................128
Table A.1
IM7/977-2 Unnotched Coupon Parameters ....................... 139
Table A.2
IM7/977-2 Notched Panel Parameters..................140
Table A.3
IM7/977-2 Unnotched Coupon Failure and Stiffness
Data ..................................
.... ......... .................
............
-13-
141
Table
Table A.4
IM7/977-2 Notched Panels Failure Data ........................... 142
Table B.1
AS4/938 Tape Layup Unnotched Coupon Parameters .......... 143
Table B.2
AS4/938 Tow Placed Unnotched Coupon Parameters...........44
Table B.3
AS4/938 Tape Layup Notched Coupon Parameters ............ 145
Table B.4
AS4/938 Tow Placed Notched Coupon Parameters.............146
Table B.5
AS4/938 Tape Layup Notched Panel Parameters ............... 147
Table B.6
AS4/938 Tow Placed Notched Panel Parameters.................. 148
Table B.7
AS4/938 Tape Layup Unnotched Coupon Failure and
Stiffness Data ............................................................... 149
Table B.8
AS4/938 Tow Placed Unnotched Coupon Failure and
Stiffness Data ............................................................. 150
Table B.9
AS4/938 Tape Layup Notched Specimens Failure
D ata ............................................................................ .151
Table B.10
AS4/938 Tow Placed Notched Specimens Failure
Data ..............................................................................
-14-
152
NOMENCIATURE
a
half length of slit
dbolt
diameter of jig bolt
E
modulus of elasticity
G
shear modulus
Hc
laminate fracture parameter in Mar-Lin correlation
KIC
fracture toughness
m
singularity from Mar-Lin correlation
M
torque applied to jig bolt
nbolt
number of jig bolts
ns
number of shear planes in jig
p
maximum load introduced through shear to each jig bolt
2r
size of discontinuity
W
width of specimen
Y1
finite width correction factor
strain
coefficient of friction between jig plates and specimen
Pstrain
microstrain (=10-6 strain)
of
failure stress
stress in the transverse direction
0
y(far-field)
far-field stress in the transverse direction
transverse far-field stress with finite width corrections
V
Poisson's Ratio
AS438
graphite/epoxy prepreg used in the investigation
CLPT
Classical Laminated Plate Theory
-15-
GPa
Gigapascals (=109 pascals)
Hz
Hertz
IM7/977-2
graphite/epoxy used in the investigation
in
inches
kN
Kilonewton (=103 newtons)
LEFM
Linear Elastic Fracture Mechanics
min
minutes
mm
millimeters
MCLAM
computer code used for progressive failure analysis
MPa
Megapascals (=106 pascals)
sec
seconds
TELAC
Technology Laboratory for Advanced Composites
-16-
Chapter 1
INTRODUCTION
Advanced composite materials consist of reinforcements, such as
glass or graphite fibers, that are impregnated in a resin or binder. The
usage of these materials in aerospace structures has increased
significantly in the past decade.
The main advantages of composite
materials are their high strength-to-weight and stiffness-to-weight ratios.
By using composite materials, weight savings of 5% to 30% can be realized
over conventional metal structures.
In commercial air transports, this
advantage translates into lower fuel costs, greater operating range and
higher payloads.
Composite materials also have greater fatigue and
corrosion resistance than metals, leading to a longer service life and lower
maintenance costs.
Presently, composite materials are utilized in primary and
secondary structures in aircraft. The Beechcraft Starship I, for example,
has an all-composite airframe.
Examples of military and commercial
aircraft that utilize composites in secondary structures include the
McDonnell Douglas F/A-18, Northrop F-117A, Airbus A320 and Boeing 767.
Boeing may use composite materials in the fuselage of its next generation of
wide body commercial aircraft.
The high level of confidence that is required for the use of composite
materials in primary structures of civilian transport aircraft, equivalent to
that established for conventional metals, has yet to be achieved. Composite
materials have different elastic properties than metals and they fail by
different mechanisms. Reliable analytical techniques have been developed
-17-
to predict the elastic behavior of composite materials. Failure behavior, on
the other hand, is still not fully understood.
Current state-of-the-art
understanding of failure mechanisms can be used to bound failure loads
and predict sensitivities to various design parameters such as layup.
Testing is still required to prove that a structure is capable of withstanding
design loads.
There is substantial room for improvement in the
understanding of composite failure mechanisms, and substantial pay-offs
if this improvement simplifies the design and certification of composite
structures.
The area of interest addressed by this investigation is the effect of
strain rates on the fracture of composite laminates containing damage.
Composite structures may be damaged in service, and subsequently may be
subjected to a variety of loading conditions. Primary composite structures
must be able to tolerate damage, i.e., they must be able to survive the
destruction or degradation of a small region and continue to perform for a
specified period of time. Severe damage propagation leading to an eventual
catastrophic failure of the structure is unacceptable.
Damage to composite structures not only includes visible
penetrations on the exterior but also less obvious damage beneath the
surface. Visible damage can be caused by errant fan blades or bird strikes,
while less obvious damage can be caused by a tool dropped during
maintenance, or a stone kicked up from the runway during takeoff or
landing. Also, realistic composite structures are designed with features
such as free edges and cutouts. These features cause stress concentrations
very similar to those caused by damage. Graphite/epoxy composites are
brittle materials, and their tensile strengths can be severely degraded by
damage and stress concentrations.
-18-
Composite structures in service are subjected to variable loading
conditions. In addition to regular aerodynamic and cabin pressure loads,
loading conditions also include gusts, sudden maneuvers, landing shocks,
depressurizations and impacts. The strain rates invoked in these events
vary drastically and these variations may affect the response of the
structure.
In the worst case, high strain rates may cause premature
failure of the structure.
The effects of variable strain rates on composite structures are not
well understood. Currently, most of the published strength data of various
composite material systems is obtained experimentally at the 'static' rate,
at approximately 0.005 e/min. This strain rate is also assumed in the
formulation of failure prediction methodologies for unflawed and flawed
composites. However, it is not known if damage mechanisms observed at
the 'static' rate are still applicable at higher strain rates. Therefore, there
is a necessity to conduct an investigation to identify strain rate sensitivity, if
any, on damaged composite structures.
The technique used to manufacture advanced composite materials
may affect the quality of the structure and its ability to withstand damage.
The traditional method of laying up composite materials is manual layup.
In recent years, automated or semi-automated methods have been used to
simplify various aspects of the manual layup operation. These include the
use of machines to perform the laying, cutting and trimming of plies. An
automated method of laying up composites, known as tow placement, is
relatively new in the composite manufacturing industry. It involves using
a machine that is programmed to process individual tows of fibers and
position them precisely next to each other. This method is especially
-19-
efficient when laying up a contoured surface. However, little data on the
performance of laminates manufactured using this technique is available.
In this investigation, the effects of strain rate on composite failure
were studied experimentally. The material systems used were IM7/977-2
and AS4/938 graphite/epoxy. The former is a 'toughened' (i.e., high strainto-failure) resin composite.
investigation.
It was used for preliminary tests in this
The latter material was used in the bulk of this work.
AS4/938 specimens manufactured by manual tape layup and automated
tow placement were tested. Tensile tests were conducted on both unflawed
and flawed specimens over strain rates ranging from 0.0042 e/min to
2 e/min.
Load, stroke and strain data were collected from each test.
Longitudinal and transverse strains were collected from the unflawed
specimens; strains were collected from strategic points (e.g., far-field and
near flaw) on the flawed specimens. The raw data was reduced to laminate
elastic properties, failure loads, approximate damage initiation loads,
strain distributions near flaws and Mar-Lin damage tolerance parameters.
It was found that the elastic properties and undamaged failure
strengths are independent of both strain rate and manufacturing
technique. In contrast, damage tolerance of these materials is significantly
strain rate dependent.
technique.
It is also strongly dependent on manufacturing
It appears that the mechanism by which damage progresses
from the existing flaw to final failure of the specimen is sensitive to strain
rate and manufacturing technique.
A literature review on the topic of composite fracture at different
strain rates is presented in Chapter 2. This chapter contains a review of
the failure prediction methodologies applicable to both unflawed and flawed
composites, previous work done in the area of strain rate effects, and an
-20-
overview of the manual tape layup and automated tow placement
manufacturing techniques.
presented.
In Chapter 3, experimental procedures are
An account of the preparation of specimens, testing, data
acquisition and reduction of data is given. Chapter 4 presents the results
obtained in this experimental investigation.
Further discussions and
possible explanations of the findings are presented in Chapter 5. Chapter 6
presents conclusions and recommendations for subsequent investigations.
-21-
Chapter 2
BACKGROUND
This chapter presents reviews and discussions on three topics: the
fracture of notched and unnotched composite laminates, strain rate effects
on composite behavior, and an overview of manual tape layup and
automated tow placement manufacturing techniques.
2.1
Fracture ofCom site
minates
The study of composite fracture has been aggressively pursued in the
last twenty years. This section examines the theories and correlations used
to predict failure of both unnotched and notched composite laminates.
2.1.1 Unnotched Specimens
In this section, existing theories on the failure of composite
laminates are reviewed.
Nahas [1] surveyed 30 failure criteria for
composites and he classified them into 4 different categories: the limit
criteria, the interaction criteria, the tensor polynomial criteria, and the
direct laminate criteria. The first category involves failure theories, e.g.,
maximum stress and maximum strain [21, that stipulate failure when a
stress or strain parameter reaches its limit.
No interaction between
stresses is accounted for but the failure mode is identified. Failure criteria
in the second category, e.g., Hill [3], Hoffman [4], use a quadratic formula
of stress. Failure occurs when this formula is satisfied. The onset but not
the mode of failure is predicted. The third category of failure criteria, e.g.,
Tsai-Wu [51, Gol'denblat-Kopnov [6], is similar to the second, except that
more general formulae are evaluated. Different tensile and compressive
-22-
strengths and all possible quadratic interaction terms are accounted for.
Again, the onset and not the mode of failure is predicted. The last category,
e.g., Puppo-Evensen [7] consists of failure criteria that can be directly
applied to the entire laminate.
Lamination theory or constitutive
assumptions are not involved. This category of failure criteria requires
experimental determination of laminate strength for every new design.
Laminate failure can be predicted by either the ply-by-ply approach or
total laminate approach. The former treats the laminate as consisting of
many bonded layers. These layers are treated as homogenous, orthotropic
materials. Using Classical Laminated Plate Theory (CLPT) [81, the ply
stresses and strains in each ply are obtained and any of the failure criteria
in the first three categories described above applied to each ply. The failure
envelopes are obtained for all plies and the innermost envelope is selected
as the laminate failure envelope. The total laminate approach considers
the entire laminate as a homogenous and anisotropic material. CLPT is
not used and the failure criteria are applied directly to the laminate. This
approach requires strength characterization of the entire laminate. The
ply-by-ply approach requires only strength characterization of one ply.
The ply-by-ply approach predicts the first ply failure (FPF) load, i.e.,
when the first ply will fail. Often, the laminate as a whole will not fail at
this load. Progressive failure of a laminate can be analyzed by removing or
degrading the properties of a failed ply, recalculating the laminate
properties, and again applying a failure criterion to the remaining plies.
This procedure is repeated until all plies have failed. The maximum load
reached is often referred to as the last ply failure (LPF) load. Specific
procedures for this kind of analyses include the Hahn-Tsai method [9], the
-23-
Chou-Orringer-Rainey method [101 and the Petit-Waddoups method [11],
just to name a few.
The results of progressive failure analyses are dependent on the
choice of ply failure criteria and failed ply degradation method. The
degradation modulus are often arbitrary, and the continued use of ply-byply failure criteria in a damaged laminate is problematic [12]. These
methods are, however, useful for bounding the laminate failure strength
and achieving insight into the laminate failure process.
2.1.2 Notched Specimens
Early researchers used Linear Elastic Fracture Mechanics (LEFM)
to model the behavior of composites with notches [131. In classical LEFM,
the failure stress is predicted by the expression:
of = KIC (7ar) -0.5
(2.1)
where of is the notched failure stress, KIC is the fracture toughness and r is
half of the crack length.
This theory provides good correlation with
experimental results of unidirectional laminates but not angle-ply
laminates.
According to an overview on notched composite laminate
analyses and experimental work complied by Awerbach and Madhukar
[14], two major approaches were undertaken by researchers in this area.
One of them is an extension of LEFM concepts while the other explicitly
considers the stress distribution at the notch.
The Mar-Lin prediction is an extension of LEFM concepts that
accounts for the inhomogeneity of composite materials. Lin and Mar [15]
contended that for composites, the mathematical stress singularity at the
-24-
notch tip should not be set at 0.5. Their expression for predicting the
fracture stress is:
of = HC (2r) -m
(2.2)
where Hc is known as the laminate fracture parameter [16] and m is the
stress singularity of the notch tip at the fiber/matrix interface.
The
variable, m, is governed by the shear moduli and Poisson's ratios of the
fiber and matrix. In the Mar-Lin equation, it is the length and not the
shape of the discontinuity that determines the failure stress. The laminate
fracture parameter, Hc, is a function of the laminate and it is determined
experimentally. Fenner found the value of m for graphite/epoxy to be 0.28
[171.
Correlation of experimental results with the Mar-Lin failure
prediction using this m value was good in some cases [18, 19] and not so
good in others [20]. The best fits of the Mar-Lin equation with experimental
data did not correspond to an m value of 0.28. Lagace [20] attributed these
variations to fracture resulting from interlaminar stresses, instead of inplane stresses. Although Hc is laminate and stacking sequence dependent,
it is not dependent on notch geometries. Hence, the laminate fracture
parameter determined from a single notch geometry can be used to
correlate results obtained from testing other kinds of notches within the
same laminate type.
Whitney and Nuismer [21, 22] formulated the point stress and
average stress criteria for predicting the failure stresses of composite
laminates in the presence of holes and slits. These criteria represent the
other approach where the concept of the damage zone, analogous to the
plastic zone found in metals, is utilized. Explicit calculations of the
-25-
stresses at the notch tip show singularity or very high values at this
location. Due to both local stress redistribution and the inhomogenous
nature of composite materials, these concentrations do not necessarily
result in failure. In both of their failure prediction methodologies, this
aspect is accounted for by assuming a characteristic length ahead of the
crack. When the stress within or at the characteristic length reaches the
unnotched failure stress, failure occurs.
In the point stress criterion,
failure occurs when the normal stress at some fixed distance ahead of the
notch equals to the unnotched tensile strength; in the average stress
criterion, failure occurs when the averaged normal stress value over some
fixed distance ahead of the notch reaches the untouched tensile strength.
These failure criteria are notch geometry dependent; the unnotched failure
strengths and the characteristic lengths of the laminate are determined
experimentally. Theoretically, the characteristic lengths in both criteria
are dependent only on the materials. However, experimental correlation
using these criteria indicates that the characteristic lengths are dependent
on layup as well [23, 24].
Another group of researchers used similar concepts of damage zones
and characteristic crack lengths to formulate their failure criterion.
Waddoups, Eisenmann and Kaminski (WEK) [25] treated the composite
material as an ideal, brittle, Griffith solid, and postulated that the energy
for crack extension is stored in a region ahead of the crack. This region has
a characteristic length which is independent of hole size. So far, all the
predictive models discussed are semi-empirical and they require a large
amount of data for successful applications.
The initiation of damage at the tip of a notch does not necessarily fail
the notched structure. This is analogous to the fact that the first ply failure
-26-
does not necessarily cause failure of an unnotched laminate. 'Progressive'
failure of a notched laminate is very complex.
Large in-plane stress
gradients exist near the notch, and the strains also vary ply by ply through
the thickness. Predicting a progressive failure involves applying a failure
criterion to all plies at many in-plane locations, and each time a failure
occurs, recalculating the stiffness and load distribution in the entire
structure.
Chang [26], for example, investigated progressive failure of
notched composites. Considerations of progressive failure can help justify
an approach such as Whitney-Nuismer's.
If failure near the notch tip
results in reduced stiffness, then the load will be transferred, and the stress
concentrations at the notch tip will be reduced.
2.2
Strain Rate Effects on Composite Lminat
m
es
Research conducted in this area covers a wide range of strain rates.
Different testing techniques and procedures are employed for tests at
different strain rates. The lowest strain rate region is associated with creep
where a constant load is applied and the strain variation with time
recorded. The effective strain rates of such test are extremely small. The
quasi-static region corresponds to strain rates up to 6 C/min [27]. In this
regime, it is assumed that no time dependent mechanisms act. Standard
hydraulic machines are capable of testing specimens at a constant strain
rate in this regime. The next strain rate region, referred to as intermediate
strain rates (up to about 3,000 e/min), are applied by means of fast-acting or
pneumatic machines and/or falling weight apparatus.
Inertia effects
become important in this rate regime. Higher strain rates, primarily in
compression, can be obtained by mechanical impact devices or explosively
generated pulses. The Split Hopkinson bar is an example of this type of
-27-
impact devices that can invoke strain rates up to 60,000 e/min in
compression. Wave propagation effects are dominant in this strain rate
regime and must be accounted for. Figure 2.1 shows the different strain
rate regimes, and the loading methods and dynamic considerations
associated with these regimes [28].
The strain rates used in this investigation are in the quasi-static
range.
Some of the reviews in this section present research that is
performed at strain rates beyond this range. Two topics on strain rate
effects on composite materials are discussed:
strain rate effects on
composite properties and strain rate effects composite failure.
2.2.1 StrainRate Effects on Composite Properties
It is well known that the mechanical properties of metals vary with
strain rates [29].
Research performed on composite materials indicates
that these materials also have strain rate dependent properties.
Strain rate effects on the longitudinal properties of unidirectional
laminates are influenced by the type of fibers present. Glass fibers are
strain rate sensitive, while carbon fibers are not [30]. Daniel et al. [31] and
Harding et al. [321 conducted tensile tests on unidirectional carbon
reinforced epoxy and the results showed no strain rate sensitivity. On the
other hand, tensile tests conducted on glass fiber reinforced epoxy showed
strain rate sensitivity.
Armenakas and Sciammarella [33] tested 00
unidirectional glass/epoxy specimens up to strain rates of 3000 elmin using
an explosively driven machine. They found that the modulus and tensile
strength increased and the ultimate dynamic strain decreased with strain
rate. These results are also confirmed in tests conducted by Harding and
Welsh [32].
-28-
o
Light Gas Gun
VELOCITY or Explosively Driven
- IMPACT
Projectile
HYPER
0
DYNAMIC
CONSIDERATIONS
IN TESTING
USUAL METHOD
()F LOADING
Shock Wave Propagation
oM
Mechanical or
Explosive Impact
Z
Ealstic-Plastic
Wave Propagation
C)
oI
oo
W
Fast Acting Hydraulic
DYNAMIC or Pneumatic Machine
Mechanical Resonance in
Specimen and Machine
I-
z
;C
o
cu)
"STATIC"
Hydraulic or
Screw Machine
Constant Strain Rate
Test
CREEP
Constant Load or
Stress Machine
Strain vs. Time of
Creep Rate Recorded
Co
0)
0D
Cv
a
Figure 2.1
Loading Regimes at Different Strain Rates.
-29-
Most resin materials, such as epoxy, are sensitive to strain rates.
Hence, the transverse properties of unidirectional laminates are also strain
rate sensitive. Daniel [31] tested 900 unidirectional laminates and showed
that the transverse modulus of carbon/epoxy unidirectional laminates
doubled and the strength increased by almost 200% at strain rates of 9,000
e/min. Daniel [341 also showed that at 300 e/min, the transverse modulus
and strength increased by about 15% and the failure strain decreased by
about 10%.
Tests conducted on angle-ply laminates also showed strain rate
sensitivity. Harding [321 tested angle-ply glass/epoxy laminates at strain
rates up to 70,000 e/min and found a large increase in strength, failure
strain and modulus with strain rate. At 9,000 e/min, Al-Salehi et al. [35]
found that while the modulus remained constant, there was a slight
increase in the failure stress and strain of the angle-ply laminates they
tested. At 180 e/min, Rotem and Lifshitz [36] found that the high strain rate
strength of angle-ply laminates was about three times higher than the
static value and the laminate modulus increased by about 50%.
The
ultimate strains remained unchanged in these tests. Daniel [34] also
conducted similar tests at this rate and obtained identical results.
Strain rate effects on compressive properties of composites were
studied by Sierakowski et al. [37] and Frey et al. [381 utilizing the Split
Hopkinson Pressure Bar at strain rates up to 12,000 e/min. They showed
that increasing the strain rates resulted in an increase in compressive
strength and different failure modes of the composite specimens.
Strain rate effects on interlaminar fracture toughness have also been
studied. Mall et al. [39] and Smiley et al. [40] showed that the interlaminar
fracture toughness of composite materials is loading rate sensitive. For
-30-
most 'toughened' resin composite materials, it decreased with increasing
strain rate. For example, tests conducted on T300/F185 decreased by 20%
over three decades of loading rates [411. For the AS4/3501-6 graphite/epoxy
material system, Mode I interlaminar fracture toughness remained
constant up to about 0.01 e/min and decreased by 70% with further increase
in strain rate. However, Aliyu and Daniel [41] performed similar tests and
found that Mode I interlaminar fracture toughness increased by 20% at the
same strain rate instead.
2.2.2 Strain Rate Effects on Composite Failure
Published papers on the mechanisms of composite failure at low and
high strain rates are rare. Mullin et al. [42] attempted to study the failure
modes of specimens made of five boron filaments embedded in an epoxy
matrix. They were tensile tested at 0.008 e/min and 0.8 /min. Examination
of the specimens tested at the slower strain rate showed more fiber breaks
than those tested at the higher strain rate. Also, the specimens failed at
higher stresses at the slower rate. The explanation given was that gradual
redistribution of load was possible at the slower rate of loading. As a break
in the fiber occurs, a slower strain rate allows stresses to be transferred, via
the matrix, to other surrounding fibers. The fibers are hence able to fail
according to their variations in strength. However, when a higher strain
rate is used, rapid propagation of fracture through the matrix occurs,
causing instantaneous loading of adjacent fibers. The failure stress at the
higher strain rate decreases because it is not possible for load to be
transferred gradually.
Although tests conducted with these kinds of
specimens are highly idealized compared to practical composites, the
results are, nonetheless, interesting.
-31-
Suvorova [43] pointed out that changes in loading rates affect the final
failure modes of composite structures. He conducted tensile tests at various
strain rates and showed that as strain rate increased, strength increased
in some regimes and decreased in others. He postulated that when damage
accumulation is the cause of final failure of a specimen, the strength of the
specimen increases with strain rate. At higher strain rates, the loading
time decreases and hence there is less time for damage to accumulate.
This results in stronger specimens.
The failure surfaces of these
specimens are rough and the fibers are pulled out of the matrix. On the
other hand, he postulated that when the dominant failure mode of a
specimen is due to the growth of macrocracks, the failure strength
decreases with increasing strain rate. As with tests conducted by Mullin et
al. on boron filaments, failure propagation is assumed to be faster at a
higher loading rate, resulting in lower failure stresses.
surfaces of these specimens are smooth and clean.
The failure
Adhesion strength
between the fibers and the matrix also plays an important role in the
transition from one mode of failure to another. Weak adhesion causes
debonding of the material and divides the fibers from the resin, thus
preventing the growth of the macrocrack. As a result, when propagation of
macrocracks is the dominant failure mode, weak fiber/matrix adhesion
delays failure propagation and results in an increase in the failure
strength of the specimen.
In summary, the literature reviewed above showed that the
mechanical properties of some of the materials present in composites, such
as most resins and glass fibers, are strain rate sensitive while others, such
as carbon fibers, are not. Also, some materials are strain rate sensitive
only above a certain strain rate.
-32-
Laminate parameters, such as
interlaminar fracture toughness, are also investigated and no conclusive
results are obtained. Varying strain rates are also shown to affect the
failure process and failure modes of unidirectional plies, angle ply
laminates, and idealized specimens such as individual boron filaments
embedded in epoxy matrices.
So far, not much information is available on the failure of
multidirectional laminates under different strain rates. There is evidence
that strengths and modes of failure are strain rate dependent.
This
dependence may vary with material, ply angle and other factors. In the
first section of this chapter, it was shown that the presence of material
discontinuities, such as holes or cracks, changes the behavior of composite
structures. These discontinuities may also affect the already complex
failure phenomenon of laminates at different strain rates.
2.3 TaIe La&M and Tow Placement Manufacturi nTechniaues
An overview of the conventional manual tape layup [44] and
automated tow placement methods [45] are presented below.
Hand layup using prepreg tape is a slow and labor intensive
procedure.
It is dependent on the skills of the individual doing the
laminating. Prepreg is a material containing the fiber reinforcement that
has been pre-impregnated with resin and then cured slightly to increase its
viscosity. It comes in rolls of various widths, typically 12 inches to 24
inches, and in various forms, unidirectional tape or woven fabric. The
prepreg is cut to the desired shape and manually laid up, layer by layer, to
the desired thickness. The assembly requires vacuum bagging and curing
at elevated temperatures in an autoclave. Laying up unidirectional tape on
a contoured tool is difficult because the tape tends to follow a geodesic path.
-33-
However, because this method is manual, a skilled individual can adapt to
variations in the tack and width of the prepreg. Unlike using automated
techniques, the tolerance of the gaps and overlaps between each layer can
be reduced and controlled by a skillful worker. Low tolerances in the gaps
and overlaps help to provide a good resin distribution in the final
manufactured part.
Automated tow placement, also known as automated fiber
placement, involves positioning unidirectional prepreg tows precisely next
to one another on a layup tool. The tows are typically 0.125 inches wide.
The tow placement machine is programmed to follow a pre-defined
geodesic path for all passes. Cutting and trimming are done automatically.
A schematic of the fiber placement process is shown in Figure 2.2 [45].
Once the laying up is accomplished, the assembly is cured. As the tow
placement machine does not have the versatility of a human being, the tows
fed into the machine have to be of exact width. Otherwise, undesirable gaps
and overlaps will occur. Also, the tack of the prepreg is important. An
excessively tacky material will gum up the chutes of the machine and
cause clogging. On the other hand, materials that are not tacky enough
will not adhere properly and maintain their position. Producing prepreg
tows with minimal width variations and the correct tack are challenges
facing the prepreg manufacturers.
Unless these obstacles are overcome,
automated tow placement will be inefficient, with extensive delays and cost
overruns caused by machine downtime.
Tow placed specimens have been tested to determine their properties
relative to that of conventional manual tape layup. Walker et al. [46]
conducted tensile tests on notched tape layup and tow placed laminates
with the same volume of fiber and matrix constituents. They found that
-34-
Figure 2.2
Schematic of the Tow Placement Process.
-35-
compared to the tape layup specimens, the tow-placed specimens had lower
notch sensitivity.
A possible explanation for the lowered notch sensitivity was the
presence of resin rich zones between the tows within each ply. These zones
facilitate ply splitting, which may lead to a more easily damaged laminate.
This process enhances redistribution of stresses around the notch tip,
resulting in higher ultimate failure strengths in the tow placed notched
specimens. There are also other material differences between the tow
placed and tape layup laminates that can account for the higher failure
strengths.
These include fiber sizing, fiber bundle size, and resin
impregnation method. So far, there has been no conclusive explanations
for the higher fracture strength of notched tow placed laminates compared
to notched tape layup laminates.
-36-
Chapter 3
EXPERIMENTAL PROCEDURE
The experimental investigation was carried out to determine the
effects of different strain rates on tensile failure of composite laminates.
Specimens were manufactured from two material systems, IM7/977-2 and
AS4/938.
They were manufactured and cut to size by Boeing.
In this
section, the test matrices used in the investigation are presented and the
rationale for their design explained.
Also, detailed specimen pre-test
preparation, instrumentation, testing, data collection and reduction
procedures are described.
3.1
Experimental A&roach
Unnotched and notched composite laminates were tested at various
strain rates and their laminate properties, failure mechanisms and modes
of failure observed.
IM7/977-2 and AS4/938 were the chosen material
systems for this investigation. The AS4/938 specimens were manufactured
by two different methods:
manual tape layup and automated tow
placement.
The IM7/977-2 specimens were 13 plies thick.
[±45/90/0/_+60/9(]s.
The layup was
The material properties and calculated laminate
properties for this system are shown in Table 3.1. Tests were conducted on
both unnotched and notched specimens. A total of 8 unnotched coupons
and 12 notched panels were tested at 4 different strain rates.
The
unnotched coupons were 50 mm wide and their gage lengths were 200 mm.
The notched panels were 203 mm wide with gage lengths of 406 mm. A
-37-
51 mm slit was machined at the center of the notched panel, perpendicular
to the loading axis. This slit size was chosen to produce a width-ofspecimen to slit length ratio (W/2a) of four. This ratio was experimentally
found to produce good correlation with analytical predictions [46]. The
configurations of the tensile test coupon and panel are shown in Figure 3.1
and Figure 3.2 respectively.
The lowest strain rate chosen for tests on the IM7/977-2 specimens
was 0.005 e/min, equivalent to the strain rate used for standard 'static' tests
at the Technology Laboratory of Advanced Composites (TELAC). Higher
strain rates were set at 0.025 e/min, 0.1 Emin and 0.5 E/min. These strain
rates covered three orders of magnitude and were evenly spaced when
plotted on a logarithmic scale. The test matrix for the IM7/977-2 specimens
is presented in Table 3.2.
The layup for the AS4/938 specimens was [T45/0/90/+30/0]s. Material
properties and calculated laminate properties for this material system are
shown in Table 3.3. Two types of AS4/938 specimens were tested: manual
tape layup and automated tow-placement.
For each specimen type, 15
unnotched coupons, 15 notched coupons with a 19 mm slit and 15 notched
panels with a 51 mm slit were tested. The coupons were 76 mm wide with
gage lengths of 178 mm and the panels were 203 mm wide with gage
lengths of 406 mm. The slits were machined at the center of the specimen
perpendicular to the loading axis. The specimen configurations are shown
in Figure 3.1 and Figure 3.2. Notched coupons and panels had the same
width-of-specimen to slit length ratio.
The three strain rates used to test the AS4/938 specimens were
0.0042 e/min, 0.1 e/min and 2 e/min. The lowest strain rate corresponds to
the 'static' rate used to conduct tensile tests at Boeing. Based on the results
of preliminary tests conducted on the IM7/977-2, 2 E/min was chosen to be
the highest rate used on the AS4/938 specimens. This was the maximum
practical rate attainable using existing hardware at TELAC. The tensile
test matrix for the AS4/938 material system is shown in Table 3.4.
32
Material Saeci• •ton and Fahricat•on
The designations IM7/977-2 and AS4/938 represent graphite/epoxy
material system. Fiber types IM7 and AS4 are graphite fibers produced by
Hercules, Inc.
Resin type 977-2, also produced by Hercules, is a
representative 'toughened' resin.
Type 938 is an untoughened resin
produced by ICI/Fiberite.
All the specimens were manufactured and cut to the required
dimensions at Boeing before they were shipped to TELAC. The following is
a brief outline of the manufacturing process and sizing of specimens
conducted at Boeing [46].
Panels were manufactured for each of the material types used in this
investigation. The panels for all the IM7/977-2 and half of the AS4/938
specimens were fabricated using the standard hand layup techniques. The
material for the tape layup process was furnished in 12 inch wide
continuous unidirectional prepreg tape. The AS4/938 tow placed specimens
were fabricated by means of the Hercules 6-axis fiber placement machine
that places twelve tows simultaneously. The panels were autoclave cured
according to the manufacturers' cure cycle. Upon completion of the curing
process, the test coupons were cut to slightly oversized dimensions with a
band saw, and subsequently sanded to the exact dimensions. A 125 surface
finish was designated for all cut edges.
-39-
Table 3.1
Material and Calculated Laminate Properties
EL
(GPa)
ET
(GPa)
VLT
GLT
(GPa)
152.1
8.5
0.35
4.2
39.5
68.5
0.28
22.9
Material
IM7/977-2
Laminate
[±45/90/0/-+60/9-0]s
Ply Thickness = 0.188 mm
Laminate Thickness = 2.44 mm
-40-
Table U2
Test Matrix for Tensile IM7/977-2 Specimens
Strain Rate (e/min)
Specimen
Type
0.005
0.025
0.1
0.5
Unnotcheda
2c
2
2
2
Notchedb
3
3
3
3
a Tensile coupon size of 350 mm by 50 mm
b Tensile panel size of 610 mm by 203 mm with 51 mm slit
c Indicates number of specimens tested
-41-
Table 3
Material and Calculated Taminate Properties
EL
ET
(GPa)
(GPa)
135.4
9.37
0.32
4.96
62.7
37.0
0.46
21.1
VLT
GLT
(GPa)
Material
AS4/938
Laminate
[445/0/90/430/05 s
Ply Thickness = 0.188 mm
Laminate Thickness =2.44 mm
-42-
Table 3.4
Test Matrix for Tensile AS4/938 Specimens
Specimen Type
Strain Rate (e/min)
0.0042
0.1
2
Unnotched Couponsa
5d
5
5
Notched Couponsb
5
5
5
Notched Panelsc
5
5
5
Unnotched Coupons
5
5
5
Notched Coupons
5
5
5
Notched Panels
5
5
5
Tape Layup:
Tow Placement:
a Tensile coupon size of 306 mm by 76 mm
b Tensile coupon size of 306 mm by 76 mm with 19 mm slit
c Tensile panel size of 610 mm by 203 mm with 51 mm slit
d Indicates number of specimens tested
-43-
Side View
Top View
7
Graphite/Epo)
Slit for
some Coupons
123 Film Adhe
Glass/Epoxy
End Tab
NOTE: Not to Scale
* for IM7/977-2 coupons, a = 76 mm, b = 200 mm, c = 50 mm
for AS4/938 coupons, a = 64 mm, b = 178 mm, c = 76 mm
Figure 3.1
Tensile Coupon Configuration.
-44-
Side View
Top View
T
102mm
0
Glass/Epoxy
°
End Tab
9q00
406mm
Slit
K- ]
51mm
FM-123
Film Adhes
0
102mm
0
0
Attachment hole
for grips
I
-4
203mm
NOTE: Not to Scale
Figure 3.2
Tensile Panel Configuration.
-45-
Inspection of the specimens upon arrival at TELAC showed that the
edges were damaged from cutting and sanding. The outer plies were split
and delaminated. These splits extended for about 3 mm inwards from the
panel edge. No attempts were made to correct these defects before the
specimens were prepared for testing.
3
PreDaration of Specmen for TestUng
Pre-test preparation of the specimens was conducted at the
Technology Laboratory of Advanced Composites (TELAC). This work was
carried out in accordance to procedures developed at TELAC. In the course
of the investigation, additional experimental methodology was developed as
required. These procedures are outlined in this section, and further details
can be found in the TELAC Manufacturing Class Notes [47].
3.3.1 Measurement of Coupons
A total of 3 width and 9 thickness measurements were taken from
each coupon. This was done to assure specimen uniformity and to compare
thickness of the specimens with nominal values supplied by the
manufacturer. A template with the thickness and width positions was
made, aligned to the center of the test section of each specimen, and the
positions marked out for measurements. Figure 3.3 shows a schematic of a
tensile coupon with the measurement points.
The measured average laminate thickness of the IM7/977-2 tensile
coupons was 2.44 mm. This corresponded to an average ply thickness of
0.188 mm, equivalent to the reported nominal value. The average width of
these coupons was 50.3 mm, compared to the nominal width of 50 mm.
Measured average laminate thickness of the AS4/938 tape layup and
tow placed coupons were 2.46 mm and 2.51 mm, corresponding to average
ply thicknesses of 0.189 mm and 0.193 mm respectively. Measured average
widths of these specimens were 77.0 mm for the tape layup coupons and
76.3 mm for tow placed coupons. The nominal ply thickness and width of
the AS4/938 specimens were 0.188 mm and 76 mm respectively. Individual
measurements for the specimens used in this investigation are tabulated in
Appendix A for the IM7/977-2 coupons and Appendix B for the AS4/938
coupons.
For all subsequent calculations used in this investigation,
nominal values for both thickness and width were used.
3.3.2 Measurement of Panels
Three width and five thickness measurements were taken from each
tensile panel. The procedure was similar to that for the coupons and a
schematic of the measurement locations is shown in Figure 3.4.
The
average laminate thickness of the IM7/977-2 panels was 2.46 mm,
translating to an average ply thickness of 0.189 mm. The average width of
these panels was 205.6 mm, compared to the nominal panel width of
203 mm.
For the AS4/938 tape layup panels, the average laminate thickness is
2.44 mm, corresponding to an average ply thickness of 0.188 mm. The
average width for these panels was 204.6 mm.
The average laminate
thickness and width of the AS4/938 tow placed panels were 2.51 mm and
203.89 mm respectively. The resultant average ply thickness was 0.193 mm
Nominal width and ply thickness of these panels were 203 mm and
0.188 mm respectively. Again, individual measurements of the specimens
are tabulated in Appendix A and Appendix B for the two respective
material systems.
Nominal values were used for all subsequent
calculations.
-47-
b*
Thickness
Measurement
Location
-
25mn
- __
T3
W1
--
n
5
T4
T7
ST
25mm
IT8
T9
120mm
"-W3
W3 Width
Measurement
Location
* for IM7/977-2 coupons, a = 200 mm, b = 50 mm
for AS4/938 coupons, a = 178 mm, b = 76 mm
Figure 3.3
Schematic of Coupon Measurement Locations.
-48-
-- W1
*T4
406mm
Gage Length
100mm,
Thickness
Measurement
Location
w
T1_
F2
---W2
T3i_5mm
JT3
Width
Measurement
Location
25mm
W3
ýT5
200mm
Figure 3.4
-
Schematic of Panel Measurement Locations.
-49-
3.&3
Attachment of Fiberglass End Tabs
Fiberglass tabs were bonded to the ends of the test specimens to
reinforce the gripping section where the tensile load was applied. The
material for the end tabs was Scotchply Reinforced Plastic Type 1002, a nonwoven crossply fiberglass reinforced epoxy resin material.
The film
adhesive used for bonding was American Cyanamid FM-123. The end tabs
had a nominal thickness of 3.8 mm. In order to ensure smooth transfer of
loads from the end tabs to the tensile coupons, the ends of the tabs nearest to
the test section were beveled to an angle of 30'. For the IM7/977-2 tensile
coupons, the tabs were 50 mm wide and 76 mm long, leaving a gage length
of 200 mm. The end tabs used for the AS4/938 tensile coupons were 76 mm
wide and 64 mm long. The resulting gage length was 178 mm. For the
tensile panels of both material systems, the end tabs were 203 mm wide and
102 mm long, leaving a gage length of 406 mm.
The end tabs were cut from 380 mm by 600 mm sheets of pre-cured
fiberglass with a bandsaw. A belt sander was used to sand the tabs to size
and to bevel one of the edges. Before bonding, the bond faces of the tabs were
roughened using 180-C Grit sandpaper and cleaned with cheesecloth and
methanol to ensure good adhesion. Also, the ends of the specimens were
cleaned thoroughly with cheesecloth and water. The tabs were placed on
the film adhesive and a razor knife was used to cut the film adhesive
around the edges. Using a heat gun to make the adhesive tacky, two tabs
were placed onto the ends of one face of the specimen with the beveled edges
facing inwards. A ruler was used to ensure that the required gage length
was achieved.
This procedure was repeated on the other face of the
specimen, so that four end tabs were in place on each specimen.
-50-
The assembled specimens with the end tabs were placed on an
aluminum caul plate to be cured in the autoclave.
The caul plate was
covered with a piece of Guaranteed Non-Porous Teflon (GNPT). A layer of
GNPT was used to cover the specimens before steel top plates were placed
on them. The steel plates were used to distribute an even loading during
the cure. The entire assembly was covered with another layer of GNPT and
four layers of fiberglass airbreather before being sealed with vacuum
bagging and vacuum tape. In the autoclave, a vacuum was drawn on the
vacuum bag and an external pressure of 0.07 MPa was applied.
The
temperature was raised at 30C/minute to 10700C, and held for 2 hours.
Cooling of the cure assembly was performed, at the same rate as the
heating, until the autoclave temperature reached 660 C. The vacuum was
vented and the autoclave was shut down.
3.3.4 Machining of Slits
Slits were manufactured at the center of some of the coupons and all
the panels. They were oriented perpendicular to the loading direction. The
slit size for the coupons was 19 mm while that for the panels was 51 mm. A
scriber was used to mark out the required slit size on the specimen. A
'starter' slit, three quarters of the required slit length, was cut using a
Dremel tool equipped with a 25 mm diameter rotary blade. The thickness of
the blade was 0.6 mm. The speed used for machining the slits was 30,000
rpm. The blade was slowly lowered by hand onto the slit marking. Starting
from the middle, a cut through the thickness of the panel was made and the
blade was carefully moved along the rest of the marking. A jeweler's saw,
with
a
nominal
thickness
of
0.5 mm,
was
used
-51-
ends notched to V-shape
I
L.
0.5mm
slit length *
* coupon slit length =19mm
panel slit length = 51 mm
Figure 3.5
Schematic Representation of a Slit.
-52-
to cut the slit to the required size. The ends of the slit were notched to a Vshape using a jeweler's saw blade with teeth filed to a point.
A schematic of a slit is shown in Figure 3.5. The nominal width of
the slit was 1 mm and the nominal tip-to-tip slit length was 19 mm for the
coupons and 51 mm for the panels. Each manufactured slit was examined
under a microscope for quality and measured with a sliding caliper. The
slit measurements for individual specimens are presented in Appendix A
for the IM7/977-2 specimens and Appendix B for the AS4/938 specimens
respectively.
The average slit length for the IM7/977-2 panels was 51.0 mm,
equivalent to the nominal value. The average slit lengths of the AS4/938
tape layup coupons and panels were 18.5 mm and 50.6 mm respectively
while that for the tow placed coupons and panels were 19.5 mm and
51.0 mm respectively. For all subsequent calculations, the nominal slit
lengths of 19 mm for the coupons and 51 mm for the panels are used.
&&5 Attachment of Mounting Jigs for Panels
Mounting jigs were used to hold the panels onto the testing machine.
The jigs consisted of four steel plates, two attached to each end of the panel.
The jig plates were attached to the panel at each end by means of five bolts.
They were tapered to fit into the grips of the testing machine. The thickness
of each jig plate was 6.25 mm. A schematic of the jig plate is shown in
Figure 3.6 [48].
Holes used for mounting the panels onto the jigs were drilled at the
ends of the specimens after the end tabs were bonded. There were five
attachment holes, 12.7 mm in diameter, on each end. The positions of the
holes were determined by placing a set of jig plates on the specimen and
-53-
marking out the center of the hole by means of a template, transfer punch
and hammer. Once the locations were marked, a 4.8 mm carbide tipped
drill was used to make a 'starter' hole. The holes were drilled to size using
another carbide tipped drill that was 12.7 mm in diameter.
A total of 10 bolts, 10 nuts, 40 washers and 2 spacers was required for
mounting a panel onto the jig plates. The side view of one end of a panel
clamped in the mounting jigs is shown in Figure 3.7. The bolts were Grade
8, 12.7 mm (0.5 inches) in diameter, 51 mm (2 inches) long with a 25.4 mm
(1 inch) shoulder. Two spacers were required at each end of the panel. The
thickness of each spacer was equivalent to that of the panel with bonded
tabs. They were made by adhering two pieces of 19 ply fiberglass cut to fit
into the spacing area. The adhesive used was Hysol 0151 epoxy patch.
Mounting of the jigs was performed by first placing two jig plates on both
sides of the panel, with the holes aligned. The spacer was then slipped
between the plates and five bolts were placed through the attachment holes.
The shoulder of each bolt was coated lightly with Bostik Never-Seez for
lubrication. Washers were attached to the bolt on both sides of the jig plates
to ensure proper tightening. The bolts and nuts were initially tightened by
hand.
The required torque for each bolt was applied by means of a torque
wrench. This was done in three stages, each stage with an increment of a
third of the final required torque. The order of tightening the bolts is shown
in Figure 3.6.
As specified by Pemberton [49], the final torque was
dependent on the maximum expected load. The equation used was:
dbolt P
S5 ( nbolt ns)
-54-
(3.1)
203mm
-
102mm
I
L
64mm
1
Above dashed
jig plates are s
by composite
i
114mm
Below dashed
jig plates are s
by glass/epox,
H-
Figure 3.6
88.9mm
Jig Plate Dimensions and Bolt Tightening Sequence.
-55-
Steel Jig
Glass/Epoxy
Spacer
Glass/Epoxy
End Tab
Bolt
Washer
Figure 3.7
Side View of Panel Secured in Mounting Jig.
-56-
where M is the torque applied to each bolt, dbolt is the diameter of the bolts, p
is the maximum load to be transferred through the joints, nbolt is the
number of bolts used, p is the coefficient of friction between the plates and
specimen, and ns is the number of shear planes.
The value for p was set as the maximum expected failure load of the
panel. For both IM7/977-2 and AS4/938 panels, p was set as 150 kN. This
value was obtained by assuming that the failure stress of the notched panel
was approximately half that of the unnotched coupon. Five bolts were used
and their diameters were 12.7 mm. There were two shear planes, one for
each jig plate, and the coefficient of friction was set at 0.18. The resulting
final torque used to tighten each bolt was 210 Nm.
3.4
Intrumentation
Both tensile coupons and panels were instrumented with strain
gages manufactured by Micro Measurements Company.
gages were used, EA-06-125-AD-120 and EA-06-031DE-120.
Two types of
The former
gages were 5 mm by 10 mm, with a gage factor of 2.055 and accuracy of
±0.5%. The latter were smaller gages, 3 mm by 6 mm, with a gage factor of
2.01 and accuracy of ±1.0%. The area on the specimens where the gages
were bonded was cleaned thoroughly with water and cheesecloth. The
gages were bonded to the specimens using catalyst and adhesive (M-Bond
200) supplied by Micro Measurements. Electrical wire leads, 460 mm in
length, were attached to the gages.
3.4.1 Unnotched and Notched Coupons
All unnotched coupons had one longitudinal and one transverse
strain gage attached. The longitudinal gage was placed at the center of the
test section while the transverse gage was placed on the centerline of the
-57-
specimen, 13 mm above the longitudinal gage. Both gages were of type EA06-125-AD-120. The strain gage arrangement for the unnotched coupons is
shown in Figure 3.8.
The notched coupons had two longitudinal gages attached.
This
strain gage arrangement is also shown in Figure 3.8. The far-field strain
gage was of type EA-06-125-AD-120.
It was placed on the specimen's
centerline, halfway between the slit and the end tab. The smaller gage, of
type EA-06-031DE-120, was placed at one end of the notch, along the axis
containing the notch. The distance from the notch tip to the middle axis of
the strain gage was 3 mm.
3.4.2 Notched Panels
The strain gage arrangement for the IM7/977-2 notched panels was
similar to that for the AS4/938 notched coupons. All the panels tested had a
far-field longitudinal gage of type EA-06-125-AD-120
attached at the
centerline of the specimen, 102 mm above the slit. The panels were also
instrumented with the smaller strain gage (type EA-06-031DE-120) located
at one end of the slit. The distance from the notch tip to the middle axis of
the strain gage was 3 mm.
All thirty AS4/938 notched panels had a far-field longitudinal strain
gage placed on the centerline of the panel, 102 mm above the slit. In
addition, twelve AS4/938 panels had a strain gage arrangement designed to
monitor the strain distribution during the tests.
This strain gage
arrangement is shown in Figure 3.9. Two tape layup panels and tow placed
panels were tested at each strain rate with this strain gage arrangement.
The arrangement consisted of three strain gages, type EA-06-031DE-120,
aligned in a straight line along the axis containing the slit, from the notch
-58-
NOTE: Not to Scale
* for IM7/977-2 coupons, a = 100 mm
for AS4/938 coupons, a = 89 mm
Figure 3.8
Strain Gage Placement for Unnotched and Notched Coupons.
-59-
NOTE: Not to Scale
Figure 3.9
Strain Gage Placement for Notched Panels.
-60-
tip to the edge of the panel. They were placed on either side of the slit. The
distances from the notch tip to the middle axes of the strain gages were
3 mm, 21 mm and 73 mm.
3.5
Testina1cedures
All tensile tests were performed on the MTS 810 Material Test System
equipped with hydraulic grips. The required strain rates for the tests were
achieved by varying the stroke rate settings of the machine. Ideally, the
strain rate is the ratio of the stroke rate setting to the specimen gage length.
However, due to the existence of load train compliance, the measured
strain rate, recorded by the far-field strain gage, was lower than this ideal
strain rate. This discrepancy will be further discussed and accounted for
in the next chapter. For all the tests conducted, the stroke rate setting was
computed from multiplying the desired strain rate by the gage length of the
specimen.
In this investigation, tensile tests were conducted at a total of 14
different stroke rates.
They are presented in Table 3.5 for each test
condition. The IM7/977-2 specimens were tested at 4 strain rates, resulting
in 8 different stroke rates as the coupons and panels had different gage
lengths. Similarly, the AS4/938 specimens required 6 different stroke rate
settings to achieve the required 3 strain rates.
Mounting of the coupons or panels in the hydraulic grips was
performed as followed: One end of the specimen was first placed between
the jaws of the upper grips. For the coupon, this referred to one end of the
specimen with the end tabs attached; for the panel assembled with the
mounting jigs, this referred to one end of the jig plates. Alignment of the
coupon was achieved by means of a machinist's square, while alignment of
-61-
the panel was done with a level. Special care was taken to make sure that
the entire coupon end tab or jig plate gripping section was inside the grips
before applying grip pressure. The upper crosshead, with the specimen
attached, was slowly lowered into the jaws of the lower grips. At this 'zero
condition', before gripping the lower jaws, the strain gages were balanced
and calibrated. The load and stroke readings were also set to zero. Again,
special care was taken to ensure that entire grip section of the specimen
was gripped. The gripping pressure for the coupons was 7 GPa and that for
the panels was 17 GPa.
Pictures of a coupon and panel prior to the
application of load are shown in Figure 3.10 and Figure 3.11 respectively.
Before starting the test machine, the data acquisition program was
activated. All tests were conducted in stroke control and ran monotonically
to fracture. At the lower rates of loading, splitting and cracking sounds
were heard during the tests and they were recorded by noting down the load
readings displayed on the testing machine.
incorporated into the recorded test data.
This information was
At the end of each test, a
photograph was taken of the failed specimen to record the failure modes.
3.6
Data Collction
Data for the tests was taken with an Apple Macintosh IIX computer
running the LabVIEW2 data acquisition software developed by National
Instruments. The hardware interface consisted of a MacADIOS breakout
box and analog/digital converter card supplied by GW Instruments. Load
and stroke readings from the testing machine were fed into a MacADIOS
breakout box, through the analog/digital converter card and recorded by the
LabVIEW2 data acquisition program. Similarly, the output from the strain
gages was fed through the Vishay Instruments Strain Gage
-62-
Table 3.5
Stroke Rate Settings and Data Collection Frequencies Used in
Tensile Tests
Specimen Type
Strain Rate (e/min)
0.005
0.025
0.1
0.5
IM7/977-2:
Unnotched Coupons
0.04a [2 ]b
0.2 [10]
0.8 [50]
4 [150]
Notched Panels
0.08 [5]
0.4 [10]
1.6 [100]
8 [200]
0.0042
0.1
2
AS4/938:
Unnotched Coupons
0.03 [2]
0.7 [50]
14.4 [750]
Notched Coupons
0.03 [2]
0.7 [100]
14.4 [750]
Notched Panels
0.07 [5]
1.7 [100]
33 [750]
a Stroke rate setting (inches/min)
b Data collection frequency (Hz)
-63-
Figure 3.10 Photograph of tensile coupon in hydraulic grips prior to
testing.
-64-
Figure 3.11 Photograph of tensile panel in hydraulic grips prior to testing.
-65-
Amplifiers/Balances, the MacADIOS breakout box and the analog/digital
converter card, and recorded by the same program.
Different data collection frequencies were used at different strain
rates to ensure that sufficient data was collected to record the tests. A total
of eight different frequencies were used in the tests. They are tabulated in
Table 3.5 with the corresponding stroke rate settings. For each test, an
average of about 200 data points were collected.
The data collection
frequencies were determined by estimating the time required to fail each
specimen configuration at each strain rate.
A custom LabVIEW2
program, written by member of the laboratory for high frequency data
acquisition, was used. This program utilizes the 'Digitize' data acquisition
module [50] and is named 'TELAC 8 Channel Fast Acquisition'.
3.7
Data Reduction
All data reduction and analysis procedures were performed using
Apple Macintosh computers. The data files created by the LabVIEW2 data
acquisition software contained columns of data points corresponding to the
data acquisition channels used during the tests. The first three channels
were used to record the load, longitudinal or far-field strain, and stroke
respectively. Additional channels were used to record readings from other
strain gages. As the data files contained extra data points collected before
and after the tests, they were 'trimmed' to a manageable size.
This
procedure was performed in the Microsoft Excel spreadsheet program,
where the initial rows of data points before any noticeable increase in
recorded stroke readings were deleted. Similarly, rows of data collected
after attaining the maximum load (i.e., the failure of the specimen), were
removed from the data file. A time column was added into the data file as
-66-
the time taken for the tests was not measured. It was determined from the
data collection frequency used and 'zero' time was set at the instant where
the stroke reading started to increase. From each 'trimmed' data file,
pertinent parameters like maximum load and the corresponding strains
were noted.
LIN6 [511 was used to compute the laminate moduli, major Poisson's
ratios, stroke rates and strain rates for all the tests. LIN6 is an algorithm
that selects linear regions of a curve, and performs linear regressions to
compute the slopes of these regions. The laminate moduli was obtained
from the slope of the stress versus longitudinal strain curve. Stress was
computed from the ratio of the recorded load to nominal cross sectional
area of each specimen configuration. The laminate major Poisson's ratio
was obtained from the slope of the transverse strain versus longitudinal
strain curve. Stroke and strain rates were obtained from the slopes of the
stroke and longitudinal/far-field strain versus time curves respectively.
The outputs for the stroke rates were linear for all the tests
conducted. However, the output for the laminate moduli, major Poisson's
ratios and strain rates showed regions of non-linearity.
The first
substantial linear region in the trimmed output, consisting of at least ten
data points, was used to calculate these properties.
-67-
Chapter 4
RESULTS
In this chapter, experimental results of strain rate effects on tensile
failure of IM7/977-2 and AS4/938 laminates are presented. These include
the failure stresses, failure modes, laminate longitudinal moduli and
major Poisson's ratio at all the strain rates tested. The strain distributions
of the AS4/938 panels are examined at varying strain rates. Also, the
notched failure strengths of the AS4/938 specimens are correlated with the
Mar-Lin theory.
All individual specimen measurements and laminate properties
recorded in this investigation are tabulated in Appendix A for the IM7/977-2
specimens and Appendix B for the AS4/938 specimens. The load, stroke
and strain gage readings collected for all the tests are shown, plotted
against time, in Appendix D and Appendix E for the IM7/977-2 and AS4/938
specimens respectively.
4.1
E ected StrinRate ersus Measud Strin Rate
The stroke rate used to conduct each test was determined by
multiplying the desired strain rate by the specimen gage length. Ideally,
this stroke rate would invoke the required strain rate in the specimen.
However, due to compliance in the load train, the actual strain rates
measured by strain gages mounted on the specimen were lower than the
ideal values. The variations between the measured strain rates and the
ideal strain rates were dependent on the specimen configurations.
Generally, the difference was about 20% for the coupons and 30% to 40% for
-68-
the panels. The measured strain rates were consistent within each set of
test configuration.
Measured strain rates for individual specimens are shown in
Appendix A and Appendix B for the IM7/977-2 and AS4/938 specimens
respectively. The 'expected' or ideal strain rate will be used to label and
categorize the various properties recorded when presenting the results.
When applicable, failure properties will be plotted using the measured
strain rates.
4.2
IM7/977-2 Test Results
The results of tensile tests conducted on unnotched and notched
IM7/977-2 laminates at four strain rates are presented below.
4.2.1
Unnotched Coupon Results
The average failure stresses of the unnotched specimens, and their
coefficients of variation, are shown in Table 4.1. At the lowest strain rate of
0.005 e/min, the average failure stress was 544 MPa. At 0.025 c/min, it was
560 MPa; at 0.1 E/min, it was 510 MPa; and at 0.5 /min, it was 565 MPa.
The average failure stresses are plotted against the measured strain rate in
Figure 4.1. The differences between the average failure stress recorded at
the 'static' rate of 0.005 E/min and those recorded at higher strain rates
were between 3% and 6%.
The failure modes of the unnotched IM7/977-2 coupons at different
strain rates were similar when inspected.
The fracture paths of all the
failed coupons were relatively straight, extending across the specimen at
an approximate angle of 300 to the loading axis. The failure surface showed
a combination of failure modes that included fiber breakage at the non-900
plies and matrix cracking at the 900 plies.
-69-
The outer 450 plies at the
Table 4.1
Average Failure Stress of IM7/977-2 Specimens at Different
Strain Rates
Average Failure Stress (MPa)
Strain Rate
(e/min)
Unnotched
Couponsa
Notched Panel b
(51 mm Slit)
0.005
544 (9 .2%)b
259 (2.7%)
0.025
560 (6.6%)
260 (0.2%)
0.1
510 (2.3%)
262 (2.1%)
0.5
565 (1.8%)
258 (4.5%)
a 2 specimens tested in each case
b 3 specimens tested in each case
c numbers in parentheses are coefficients of variation
-70-
800 700
-
Cz
600-
"E,
500-
a.
IM7/977-2
[±45/90/0/I60/90]s
Unnotched
51mm Slit
a) 400C/)
U)
L13
tz
LL
3002001000
I
0.1
-
v
0.001
Figure 4.1
0.01
Strain Rate (e/min)
Average F ailure Stress vs. Strain Rate for IM7/977-2
Specimens.
-71-
surfaces of the specimen were delaminated from the adjacent plies. The
delaminations extended for about 50 mm from the failure surface. Sketches
of the different failure modes described are shown in Figure 4.2. For some
of the IM7/977-2 coupons, failure also occurred near the end of the
specimens. These failures were perpendicular to the loading direction. A
sketch of the failure modes of the unnotched coupons described above is
shown in Figure 4.3, and a post test photograph of representative
unnotched coupons tested at the various strain rates is shown in Figure 4.4.
The stress strain curves of representative IM7/977-2 unnotched
coupons at the various strain rates tested are shown in Figure 4.5. The
stress-strain behaviors were generally linear for at least one-third of the
initial loading. After that, the curves showed load drops at about 350 MPa
and 500 MPa. The locations where the drop in load occurs corresponded to
audible 'clicks' heard and recorded during testing.
The average laminate longitudinal modulus was 35.2 GPa at
0.005 e/min, 39.7 GPa at 0.025 e/min, 37.8 GPa at 0.1 E/min and 39.1 GPa at
0.5 e/min. The laminate longitudinal modulus calculated for this layup
using Classical Laminated Plate Theory (CLPT), shown in Table 3.1, was
39.5 GPa.
The Poisson's ratio obtained experimentally was 0.26 at
0.005 e/min and 0.27 at the rest of the strain rates tested. This was
consistent with the CLPT computed value of 0.27. The average laminate
moduli and Poisson's Ratios at different strain rates, with their coefficients
of variation, are shown in Table 4.2.
4.2.2
Notched Panel Results
The average failure stress for the notched panels at the 'static' rate of
0.005 e/min was 259 MPa. At 0.025 E/min, the average failure stress was
-72-
UU
Fiber Breakage
Matrix Cracking
Delamination
UU
LIIIIIIIZ
Figure 4.2
Sketches of Different Failure Modes.
-73-
Bundle Pullout
Splitting
(a) IM7/977-2 Unnotched Coupon
(b) AS4/938 Unnotched Coupon
Delaminated Area
Matrix Splitting
Figure 4.3
Failure Modes of IM7/977-2 Unnotched Coupon and AS4/938
Unnotched Coupon.
-74-
"·~
I
Za~
·~
=~:
-~-f·
(a)
Figure 4.4
(b)
(c)
(d)
Photographs of Failed IM7/977-2 Unnotched Coupons at
Different Strain Rates.
-75-
-'I','
LA.
UU U
500 -
IM7/977-2 Unnotched
S[45/90/0/±60/90]s
*, 400 c 300(.
Strain Rate Tested:
200-
-/-
--A--- 0.025&min
- --- 0.1 elmin
--o- 0.5 E/min
100 0-
Figure 4.5
0
0.005 &min
6000
12000
Strain (gstrain)
18000
Stress-Strain Curves of IM7/977-2 Unnotched Coupons at
Different Strain Rates.
-76-
IM7/977-2 Unnotched Coupon Stiffness Data at Different Strain
Rates
Table 4.2
Strain Rate
(e/min)
Average Laminate
Longitudinal Modulus
(GPa)
Average Laminate
Poisson's Ratio
0.005
35.2 (13.4%)a
0.26 (0%)
0.025
39.7 (2.3%)
0.27 (2.7%)
0.1
37.8 (1.3%)
0.27 (0%)
0.5
39.1 (0.4%)
0.27 (2.7%)
a numbers in parentheses are coefficients of variation
-77-
260 MPa; it was 262 MPa at 0.1 e/min and 258 MPa at 0.5 e/min. These
values and their coefficients of variation are shown in Table 4.1.
The
average failure stresses of the IM7/977-2 notched panels plotted against
measured strain rates are shown in Figure 4.1.
The appearance of the failed IM7/977-2 notched panels differed at the
different strain rates tested. Failure of the notched panels started at the
ends of the slits and propagated outwards to the edges of the panels. At
0.005 e/min, fracture paths generally traveled at 600 or 900 to the loading
direction. Along the failure surface, the 00 plies failed from fiber breakage
and the 90* plies failed from matrix cracking. The other plies also failed
from fiber breakage. Minor delamination was present at the outer 450 plies
near the failure surface. At 0.025 e/min, the fracture phenomenon was
similar to that at 0.005 e/min. However, some specimens tested at this
strain rate did not break cleanly due to splitting in the matrix of the 450 and
600 plies. This resulted in the plies separating to strands about 5 mm long,
along the fiber direction. At 0.1 e/min and 0.5 E/min, none of the specimens
tested broke into separate pieces. Examination of the fracture path showed
that it was jagged and not well defined. The severity of splitting of the outer
450 plies increased with strain rates. At 0.5 /min, the
±450
plies broke into
very long and thin strands, about 100 mm long. Twisting of theses strands
from the delaminated 450 plies occurred as the panels were extended
further apart. Examination of the internal 00 and 900 plies in these panels
showed no splitting.
These plies broke by fiber breakage and matrix
cracking respectively. Sketches of the different failure modes described
above are shown in Figure 4.2. Also, sketches of the IM7/977-2 notched
panels at different strain rates are shown in Figure 4.6. A bar-chart
summarizing the different modes of failure observed in the notched panels
-78-
(a) 0.005 E/ min
(b) 0.025 E/min
(b) 0.1 e /min
(d) 0.5 c/min
Delaminated Area
Matrix Splitting
Figure 4.6
Failure Modes of IM7/977-2 Notched Panels at Different Strain
Rates.
-79-
rC
U)
E
C)
O9
00
%I--
E
z
0.005
0.025
0.1
0.5
Strain Rates (e/min)
Figure 4.7
Distribution of Failure Modes for IM7/977-2 Notched Panels.
-80-
IM7/977-2 NOT(CHED PANEI
0.005 STI'l'AIN / NI IN
1,1
ý,V' ,m v 1
S
''i 3i ..
"
&
6-
I!I R q I
- 2 I F!Ir I;
Iý,i '
'
SO
12i%
l '! 7 7 ,
LI
I
(a) 0.005 e/min
517,977-2
NOT(HlEI) PANEL
0.02.5- STRAIN / MIN
1
2
i..4
1i !
9 '
1
U
I
131
it
I1S
(b) 0.025 e/min
Figure 4.8
Photographs of Failed IM7/977-2 Notched Panels at
(a) 0.005 e/min and (b) 0.025 U/min.
-81-
11
,i
,i
~~II
i
(c) 0.1 e/min
KI) I'.\NI"A
]
977-.2 NO (TIt
(b) 0.5 e/min
Figure 4.9
Photographs of Failed IM7/977-2 Notched Panels at
(c) 0.1 e/min and (d) 0.5 E/min.
-82-
is shown in Figure 4.7. Failure due mainly to fiber breakage and matrix
cracking, with the specimen breaking into two parts, is represented as Type
A damage. Type C failure is typified by severe outer ply splitting and a
jagged fracture path, with the specimen remaining intact and held
together by the split plies. Type B damage is combination of both Type A
and Type C damages.
It represents a failure mode with less severe
splitting on the plies and a more defined fracture path. Photographs of
representative panel failure tested at the four strain rates are shown in
Figure 4.8 and Figure 4.9.
4.3
AS4/938 Tests Results
The results of testing AS4/938 unnotched and notched specimens at
three strain rates are presented below.
4.3.1
Unnotched Coupon Results
The average failure stress of the AS4/938 tape layup unnotched
coupon was 608 MPa and 598 MPa at strain rates of 0.0042 e/min and
0.1 E/min respectively. When the loading rate was increased to 2 e/min, the
average failure stress decreased to 565 MPa. The difference in average
failure stress between the slowest and fastest rate was 7%. The tow placed
unnotched specimens failed at about the same values as the tape
specimens. At 0.0042 /min, the average failure stress was 589 MPa and at
0.1 e/min, it was 605 MPa. At the highest loading rate of 2 E/min, the
average failure stress was 582 MPa. The strength results are tabulated in
Table 4.3.
Failure stresses for tape layup and tow placed unnotched
coupons are plotted against measured strain rate in Figures 4.10 and 4.11.
The failure modes of the unnotched AS4/938 tape layup and tow
placed coupons were similar. Also, there were no significant changes in
-83-
Table 4.3
Average Failure Stress of AS4/938 Specimens at Different
StrainRates
Average Failure Stressa (MPa)
Unnotched
Coupons
Notched Coupon
(19 mm Slit)
Notched Panel
(51 mm Slit)
0.0042
608 (4.4%)
279 (7.8%)
197 (8.0%)
0.1
598 (2.8%)
288 (12.2%)
189 (8.6%)
2
565 (4.4%)
227 (7.8%)
168 (16.5%)
0.0042
589 (2.6%)
351 (3.1%)
290 (3.3%)
0.1
605 (1.9%)
370 (8.7%)
293 (3.9%)
2
582 (0.8%)
339 (7.1%)
263 (8.8%)
Strain Rate
(/min)
Tape Layup:
Tow Placement:
a 5 specimens tested in each case
b numbers in parentheses are coefficients of variation
-84-
800
AS4/938 Tape Layup
700- .[T45/0/90/T30/0]s
Co
Unnotched
19mm Slit
o
A
0 51mm Slit
600500-
Cl
G)
400-
L.
300-
LL
2001000- 1
0.001
I
0.1
0.01
m
Strain Rate (e/min)
m
,
10
Figure 4.10 Average Failure Stress vs. Strain Rate for AS4/938 Tape Layup
Specimens.
-85-
800-
AS4/938 Tow Placement
700- .[T45/0/90/T30/0]s
/1_
0O
C'
C,
U)
L,..
CD
U)
600-
Unnotched
19mm Slit
51mm Slit
0
500400300-
A
-
0
0
3
L..
200100(2I-l
r
0.001
0.01
0.1
Strain Rate (e/min)
10
Figure 4.11 Average Failure Stress vs. Strain Rate for AS4/938 Tow Placed
Specimens.
-86-
the failure modes for either type of specimen when the strain rates were
varied. Sketches of the different failure modes described below are shown
in Figure 4.2. All the specimens broke cleanly in the middle of the gage
length. The fracture path was relatively straight and perpendicular to the
loading axis. On the failure surface, bundle pullout was observed on the
±450 and ±300 plies. Fiber breakage was observed in the internal 00 plies
and matrix cracking in the 90" plies.
specimens, the
±450
plies delaminated.
On the outer surfaces of the
The delamination extended
inwards from the failure surface and the delaminated surface broke after
about 10 mm to 30 mm. A sketch of the failure modes of the AS4/938
unnotched coupon is shown in Figure 4.3. Representative photographs of
the unnotched tape layup and tow placed coupons failed at different strain
rates are shown in Figure 4.12 and Figure 4.13 respectively.
The stress-strain curves of the AS4/938 tape layup and tow placed
unnotched coupons were similar. These curves at different strain rates are
shown in Figure 4.14 and Figure 4.15 respectively.
These specimens
behaved linearly and the behavior was consistent at different strain rates.
There were no visible load drops on the curves. However, 'clicks' were
heard when testing the specimens at the slower strain rates.
For the tape layup specimens, the average longitudinal moduli were
60.7 GPa, 59.6 GPa and 61.7 GPa at increasing strain rates of 0.0042 e/min,
0.1 /dminand 2 E/min respectively. Average laminate moduli for the tow
placed coupons were 60.6 GPa, 62.2 GPa and 61.9 GPa at the equivalent
strain rates. The laminate longitudinal modulus computed for this layup
from CLPT was 62.7 GPa as shown in Table 3.3. The average laminate
moduli obtained experimentally were within 3% of the value computed
using CLPT.
-87-
/ A
1
.9
r
.
..
(a)
(a)
Strain Rates:
Figure 4.12
.
-
(b)
(b)
(a) 0.0042 E/min
(b) 0.1 e/min
(c)2 e/min
Photographs of Failed AS4/938 Tape Layup Unnotched
Coupons at Different Strain Rates.
-88-
··~~··r~
~-;-__~·i·;
AS4/938 TOW-PLACED
UNNOTCHED COUPONS
(a)
Strain Rates:
I
(b)
(a) 0.0042 E/min
(b) 0.1 /min
(c) 2 c/min
Figure 4.13
Photographs of Failed AS4/938 Tow Placed Unnotched
Coupons at Different Strain Rates.
-89-
7AA
''"'
AS4/938 Tape Layup, Unnotched
600 - [_45/0/90/T30/0]s
500-
m 400CD)
300-
200-
Strain Rate Tested:
-+-
---
100-
0.0042 ermin
0.1 Emin
•--
- --2 rmin
00
2000
4000
6000
8000 10000 12000
Strain (gstrain)
Figure 4.14 Stress-Strain Curves of AS4/938 Tape Layup Unnotched
Coupons at Different Strain Rates.
-90-
700
AS4/938 Tow Placed, Unnotched
_T45/0/90/T30/0]s
600
500
CL
C,
C,
L.
400
300
200
Strain Rate Tested:
---
-
100
0.0042 e/min
x- 0.1 emin
-- - 2 dmin
0
I
0
II
2000
I
I
I
4000 6000 8000 10000 12000
Strain (microstrain)
Figure 4.15 Stress-Strain Curves of AS4/938 Tow Placed Unnotched
Coupons at Different Strain Rates.
-91-
Table 4.4
AS4/938 Unnotched Coupon Stlffness Data at Different Strain
Rates
Strain Rate
(e/min)
Average Laminate
Longitudinal Modulus
(GPa)
Average Laminate
Poisson's Ratio
Tape Layup:
0.0042
60.7 (3.2%)
0.48 (2.4%)
0.1
59.6 (3.0%)
0.47 (3.0%)
2
61.7 (3.8%)
0.50 (3.2%)
0.0042
60.6 (1.8%)
0.48 (6.2%)
0.1
62.2 (2.1%)
0.51 (5.3%)
2
61.9 (3.8%)
0.48 (4.6%)
Tow Placement:
a numbers in parentheses are coefficients of variation
-92-
The laminate major Poisson's ratios for the tape layup and tow
placed specimens were also insensitive to the strain rates tested. The
Poisson's ratio calculated from CLPT was 0.46. The average experimental
value obtained for the tape layup coupons at 0.0042 e/min was 0.48. It was
0.47 at 0.1 e/min and 0.50 at 2 e/min. The average Poisson's ratios for the
tow placement coupons were 0.48, 0.51 and 0.48 at 0.0042 e/min, 0.1 e/min
and 2 e/min respectively. Average laminate moduli and Poisson's ratios for
the AS4/938 specimens, and their coefficients of variation, are shown in
Table 4.4.
4.3.2
Notched Specimen Results
The average failure stress for tape layup notched coupons was
279 MPa at the strain rate of 0.0042 E/min. At 0.1 e/min, the average failure
stress was 288 MPa and at 2 e/min, the average failure stress decreased to
227 MPa. The difference in strength values between the slowest and fastest
rates was 19%. Results obtained from the tape layup notched panels
showed the same trend. At the 'static' rate of 0.0042 c/min, the average
failure stress was 197 MPa and at 0.1 e/min, it was 189 MPa. When the
loading rate was increased to 2 E/min, the average failure stress was
168 MPa, a decease of 15% from the 'static' rate.
Average failure stress results for the tow placed specimens showed
less sensitivity to strain rates. Tow placed notched coupons failed, on the
average, at 351 MPa, 370 MPa and 339 MPa at strain rates of 0.0042 E/min,
0.1 E/min and 2 e/min respectively. From the 'static' strain rate of
0.0042 e/min, the average failure stress increased by 5% at 0.1 e/min and
decreased by 3% at 2 e/min. The average failure stresses for the tow placed
panels were 290 MPa, 293 MPa and 263 MPa from the slowest to the highest
-93-
rate. The difference between the average failure stress of the panels at the
slowest and fastest rate was 9%.
Notched specimens manufactured using automated tow placement
exhibited higher failure strengths than those manufactured using manual
tape layup. At 0.0042 e/min, average failure stress differences between the
tape layup and tow placed specimens were 26% for the coupons and 47% for
the panels. At 0.1 e/min, the differences were 28% for the coupons and 55%
for the panels; and at 2 /min, the differences were 49% for the coupons and
56% for the panels.
The average failure stresses and coefficients of
variation for all notched specimens are summarized in Table 4.3. Failure
stresses of the tape layup and tow placed specimens are plotted against
measured strain rates in Figure 4.10 and Figure 4.11 respectively.
The tape layup and tow placed notched specimens had different
failure modes. A sketch illustrating the differences in the failure modes of
the notched tape layup and tow placed specimens is shown in Figure 4.16.
Photographs taken of typical failed specimens of each type are shown in
Figure 4.17. The failure modes were very consistent within each specimen
type. They were not sensitive to strain rate.
The fracture path of the tape layup specimen was straight and
perpendicular to the loading axis. The outer 450 plies on the top and bottom
surfaces delaminated and split into strands about 30 mm long, which
remained attached to the plies. Underneath, the rest of the laminate failed
mainly due to fiber breakage and matrix cracking. The failure surface
was smooth and straight.
The failure modes of the AS4/938 tow placed notched specimens were
different. Failure initiated at the notch tip and the failure path was jagged
and rough. The failure path did not cut through all the plies at the same
-94-
(a) AS4/938 Tape Layup, Notched
(b) AS4/938 Tow Placement, Notched
Delaminated Area
U
IT•
Matrix Splitting
Figure 4.16 Failure Modes of AS4/938 Tape Layup and Tow Placed Notched
Specimens.
-95-
--
~1!r I6
8
.
9
10
12
1I
13
14
6
1,
17
1
P,
2
Nn -4
21
2
Tape Layup
i -#Jk
9
21.-
3
1
5
6
7
1
9's'"I 10
M~iwý-CENO-
1)
12
123
14
Ls
S
0
7
1~
8
~ 11
2Q
Tow Placed
Figure 4.17
Photographs of Typical Failed AS4/938 Tape Layup and Tow
Placed Notched Specimens.
-96-
(a)
Strain Rates:
Figure 4.18
(a) 0.0042 e/min
(b) 0.1 P/min
(c)2 E/min
Photographs of Failed AS4/938 Tape Layup Notched Coupons
at Different Strain Rates.
-97-
T 77
21
t;--- -
%e
o
(a)
Strain Rates:
Figure 4.19
c
;;i
d4
(b)
(c)
(a) 0.0042 e/min
(b) 0.1 e/min
(c) 2 e/min
Photographs of Failed AS4/938 Tape Layup Notched Panels at
Different Strain Rates.
-98-
(~1lt:Iwze = ilmm)
(a)
Strain Rates:
Figure 4.20
o
¶
I
(b)
(a) 0.0042 e/min
(b) 0.1 e/min
(c) 2 e/min
Photographs of Failed AS4/938 Tow Placed Notched Coupons
at Different Strain Rates.
-99-
Strain Rates:
(a) 0.0042 /min
(b) 0.1 Emin
(c)
Figure 4.21
2 e/min
Photographs of Failed AS4/938 Tow Placed Notched Panels at
Different Strain Rates.
-100-
location as different sets of plies were observed to have their own distinct
failure surfaces. The 00 and 900 plies failed perpendicular to the loading
axis due to fiber breakage and matrix cracking respectively; the other plies
failed at an angle to the loading axis, notably, the 450 plies, which failed by
matrix splitting. Delamination was present through the thickness of the
specimens and it was especially severe at the outer 450 plies. Sketches of
the failure modes described above are shown in Figure 4.2. Representative
photographs taken of the AS4/938 tape layup specimens are shown in
Figure 4.18 and Figure 4.19; representative photographs of the tow placed
specimens are shown in Figure 4.20 and Figure 4.21.
4..&3
Strain Distribution of Notched Panels
Twelve AS4/938 notched panels were instrumented with strain gages
to monitor the strain distribution from the notch tip to the edge of the
panels. Three strain gages were used. They were aligned along the axis of
the slit. The distances from the notch tip to the centerline of the gages were
3 mm, 21 mm and 73 mm. Six tape layup and six tow placed panels had
this strain gage arrangement. The panels were tested at the three strain
rates, two at each rate.
Tape layup and tow placed panels showed identical strain
distribution behaviors.
They are averaged together and shown in
Figure 4.22, Figure 4.23 and Figure 4.24 for panels tested at the three strain
rates.
Strain distribution plots for the individual panels tested are
presented in Appendix C. Recorded strains at each gage location were
normalized by the recorded far-field strains to produce the strain
concentration factor. They were plotted against the distance from the notch
tip to the specimen free edge.
-101-
The strain distributions were also compared to Lekhnitskii's
analytical expression used for computing normal stresses ahead of a crack
The
in a notched orthotropic laminate under uniaxial loading [52].
expression used was:
Oy (x,0) =
(4.1)
2
x2 - a2
The origins of the coordinates, x and y, are at the center of the crack with
the x-axis in line with the crack and the y-axis on the centerline of the
specimen.
7y is the normal stress at the mid-plane (y=O) and the x
coordinate ranges from a slight distance from the crack tip to the edge of
the laminate. oy is the far-field stress corrected for finite width effects and
the slit length is 2a. This expression is independent of material properties
and can be used for either isotropic or orthotropic laminates.
The finite width correction factor (Y1) for isotropic materials was
used in the computations. It was approximated by the expression [53]:
Y1(
2a
) = 1 + 0.128
2a
2a
2a
- 0.288 (')2 + 1.52 ()3
(4.2)
where 2a is the slit length and W is the width of the specimen. For the
AS4/938 panels, the slit length to width of specimen ratio is 4, resulting in a
finite width correction factor of 1.04.
In the plots, the normal stress corrected for finite width effects was
normalized by the far-field stress. The resulting expression was used for
plotting the prediction curves:
_
y
(;Y
(x,0) =
Oy(far-field)
1.04 x
-x2.
-102-
2
(4.3)
h
AS4/938 Notched Panel, 51 mm Slit
Strain Rate = 0.0042 d/min
A 20% Load
"- 2.5-
0 50% Load
O 80% Load
+o
aO
ca
L.
-n
Prediction
2-
1.5-
.1
I
1-
0
I
I
I
I
I
I
I
60
45
30
15
Distance from Tip of Notch (mm)
75
Figure 4.22 Average Strain Distribution of AS4/938 notched panel at 0.0042
strain/min.
-103-
C
t"0
Cz
LL
LL
C
Ctcn
o•
0
0
-J
0
60
45
30
15
Distance from Tip of Notch (mm)
75
Figure 4.23 Average Strain Distribution of AS4/938 notched panel at 0.1
strain/min.
-104-
C
-4
U)
.j
CU
L
"10
LL
-a,
2.5
2
L__
O3
I
r
1.5
o
0
_J
0
15
30
45
60
Distance from Tip of Notch (mm)
75
Figure 4.24 Average Strain Distribution of AS4/938 notched panel at 2
strain/min.
-105-
Also, the x-axis in the plots was shifted so that the origin was at the notch
tip instead of the center of the slit. The above stress concentration was
assumed to be the same as the strain concentration at low loads. This will
be true as long as the laminate modulus remains constant.
At 0.0042 c/min, as shown in Figure 4.22, the average strain
concentration recorded at 20% of the maximum stress agreed with the
analytical prediction at all the three locations on the panel. When the
stress level was increased to 50%, the average strain concentration
recorded at the gage nearest to the notch tip increased.
The strain
concentrations at the other two locations remained the same. At 80% of the
maximum stress level, the gage at the notch tip produced erratic readings.
The middle gage showed a substantial increase in average strain
concentration and the gage at the edge also recorded at slight increase in
average strain concentration. The strain behavior of the laminate tested at
0.1 E/min, as shown in Figure 4.23, was very similar to that at 0.0042 c/min.
Tests conducted at 2 e/min for both tape layup and tow placed panels
showed a peculiar strain distribution. The average strain distribution is
shown in Figure 4.24.
At 20% of the maximum stress, the strain
concentrations recorded at the notch tip and middle gages were similar to
that predicted by the analytical expression.
However, the strain
concentration at the third gage located at the edge of the panel was higher
than the predicted value.
This phenomenon was consistent for strain
concentrations compiled for all the tests conducted at 2 e/min. It was also
independent of specimen type.
The consistency of the strain gage recordings at the panels edge at
2 e/min rule out experimental error or the existence of test artifacts. Also,
the behavior cannot be attributed to the different specimen type: tape layup
-106-
and tow placed specimens behaved similarly. Upon reexamining the failed
specimens, it was found that these gages had been attached to material
damaged during specimen cutting. The top plies were badly split and
delaminated for about 3 mm in from the cut edge and the gages had been
attached to this damaged material. The results hint that edge effects may
be strain rate dependent, but it is unclear if this effect contributes to
specimen failure. It was observed in both the strain rate sensitive tape
layup panels and the strain rate insensitive tow placed panels.
4.3.4
Mar-Lin Correlation of Notched Specimens
Failure stresses of the notched AS4/938 specimens were correlated to
the Mar-Lin equation (2.2) and used to determine laminate fracture
parameter. The value for the stress singularity (m) was set at 0.28. The
laminate fracture parameter (HC) was calculated individually for each
specimen tested. The measured slit size was used in this calculation. The
HC values were then averaged for each strain rate and specimen type. The
average fracture parameter for the AS4/938 notched tape layup and tow
placed specimens is shown in Table 4.5. Mar-Lin curves relating failure
stresses to slit length were plotted using these average values of HC.
Figure 4.25, Figure 4.26 and Figure 4.27 show the individual failure
stresses of the tape layup and tow placed specimens plotted with the MarLin curves at 0.0042 e/min, 0.1 e/min and 2 e/min respectively.
The
measured slit lengths were used in these plots.
The laminate fracture parameter, HC, is a measure of the damage
tolerance of the specimens. The results showed good correlation between
the experimentally obtained failure strengths and the Mar-Lin predictions.
This correlation reinforces the previously noted result that although the
-107-
unnotched failure strengths are relatively independent of manufacturing
techniques and strain rates, the damage tolerance is strongly dependent on
both of these parameters.
-108-
Table 4.5
Average Mar-Lin Fracture Parameter (He) for AS4/938
specimens at Different StrainRates
Strain Rate
(E/min)
HC
(MPa*mm0. 2 8 )
Coefficient of
Variation
Tape Layup:
0.0042
612
8.0%
0.1
610
12.4%
2
508
12.2%
0.0042
840
5.1%
0.1
865
6.5%
2
783
7.5%
Tow Placement:
-109-
600-
AS4/938 Specimens
[T/45/0/90/W30/0]s
Tested at 0.0042 /min
500 CO
400 C1)
(0
Cf
I.-
LL
300 **------~..
200100
-------- H (Tow)=840 IMPa*mm0.
Failure Stress:
28
- Hc(Tape)=612 MPa*mm0 . 28
0I
I
20
O Tow
A Tape
I
·
40
60
Slit Length 2a (mm)
e
80
Figure 4.25 AS4/938 Notched Failure Stresses and Fracture Prediction
Curve at 0.0042 e/min.
-110-
600- I
I
-
AS4/938 Specimens
[T45/0/90/T30/0]s
Tested at 0.1 e/min
500 -A
a(I)
400 -
C,,
cfz
300 -
''' ''' '" ''
U.
ed
A
0)
L_
200 -
A
100 - -..------- H(Tow)=865 MPa*mmO. 28
-
- H (Tape)=610 MPa*mm 0.28
Failure Stress:
O Tow
A
Tape
W
20
40
Slit Length 2a (mm)
60
80
Figure 4.26 Notched AS4/938 Specimens Failure Stresses and Fracture
Prediction Curve at 0.1 /min.
-111-
600
=-
AS4/938 Specime_ns
[T45/0/90/T30/0]s
Tested at 2 ,/min
500
a2400
cn
A
300
0O
200
~-
U.
100 - ........
6
• --~ . ()--.
Hc(Tow)=783 MPa*mm 0. 28
Failure Stress:
O Tape
- H (Tape)=508 MPa*mm0.28
Sv
-
Tow
I
-
20
A
40
Slit Length 2a (mm)
1o
60
I
80
Figure 4.27 AS4/938 Notched Failure Stresses and Fracture Prediction
Curve at 2 c/min.
-112-
Chapter5
DISCUSSION
In this chapter, a discussion of the experimental results is
presented.
Trends observed in the behavior of laminate failure under
varying strain rates are identified and possible explanations proposed.
5.1
trainRte Effects on
IM/9 -2B7
Snep
mns
The results of tests conducted on the IM7/977-2 unnotched and
notched specimens are discussed below.
5.1.1
Unnotched Coupons
The failure modes, failure stresses, laminate longitudinal moduli
and Poisson's ratios observed and measured for the IM7/977-2 unnotched
coupons are insensitive to the range of strain rates tested.
The failure of the unnotched coupons is analyzed using a progressive
failure model implemented as a computer code dubbed MCLAM.
The
model utilizes Tsai-Wu's stress quadratic interaction criterion [5].
Progressive failure in this analysis is achieved by reducing the transverse
and shear moduli of failed plies by 0.5. The plies' longitudinal modulus
and major Poisson's ratio remain unchanged. The predicted stress-strain
behavior of the unnotched specimens is shown in Figure 5.1.
The
experimental stress-strain curves used in the plot are obtained from typical
tests conducted at 0.005 e/min and 0.5 e/min. The prediction correlates well
with the experimental results. Load drops in the experimental stressstrain curves and final failure of the coupons are fairly well predicted by the
model. Load drops corresponding to failure of the
-113-
±450
plies are most
distinct in the experimental stress-strain curves. Audible clicks heard and
recorded during the tests coincide with the observed load drops.
The layup of the IM7/977-2 specimens is fairly 'soft' compared to that
of the AS4/938 specimens. The non-zero plies are oriented at 450, 600 and
900. Also, the resin type 977-2 is a 'toughened' resin. The layup softness
and resin toughness combine to produce a progressive type of failure in
these laminates.
5.1.2
Notched Panels
Failure stresses of the IM7/977-2 notched panels are insensitive to the
range of strain rates tested. The average failure stress of the panels is
about 45% of the unnotched failure stress. The IM7/977-2 tape layup panels
are less notch sensitive than the AS4/983 tape layup panels.
Strain readings collected for a typical notched panel are shown in
Figure 5.2. The curve representing the notch tip strain is fairly linear
initially. At a modest fraction (less than 60%) of the final failure time,
kinks start to appear and the curves become non-linear. The kinks in the
curve are responses to a decrease in stiffness in the region near the strain
gage due to damage beneath the gage. When these kinks occur in the
readings from the gage situated closest to the notch tip, the onset of failure
is implied. The applied load at which the kinks first occur is recorded and
assumed to represent the failure initiation load.
The average far-field stresses at which the initiation of failure occurs
in the notched panels are tabulated in Table 5.1. The recorded stresses are
also normalized by the final failure stresses. Representative plots of the
notch tip strain at the different strain rates are shown in Figure 5.3. The
results show that the failure initiation stresses for the panels are similar at
-114-
800
IM7/977-2 Unnotched
700 - [+45/90/0/±+60/9-0]s
600
500
C
CL
400
CA
CO> 300
2
200
100
0
I
0
4000
8000
12000
16000
Strain (microstrain)
Figure 5.1
Experimental and Predicted Stress-Strain Curves of IM7/977-2
Unnotched Coupons.
-115-
15000
IM7/977-2, 51 mm Slit
Tested at: 0.025 c/min
(Specimen M1-LNO9)
. 10000
Failure Initiation
Final Failure
C5000
cn 5000
----
0I
0
Figure 5.2
Far-Field Strain
-- [- Notch-Tip Strain
10
15
20
Time (sec)
25
30
Strain Readings Collected of Typical IM7/977-2 Notched Panel.
-116-
16000 -
IM7/977-2 Notc_hed, 51 mm slit
12000 C'
8000 CZ
Lat Strain Rates:
0.005 e/min
0.025 dmin
0.1 emin
0.5 &min
4000 -
0-
I
)
I
I
0.2
0.4
_
0.6
0.8
Time / TimeFailur
e
Fallure
Figure 5.3
Plot of Notch Tip Strain versus Normalized Time of
Representative IM7/977-2 Notched Specimens at Different
Strain Rates.
-117-
Table 5.1
Average Stress at Failure Initiation and Ratio of Initiation
Stress to Failure Stress for the IM7/977-2, 51 mm Notched
Specimens
Strain Rate
(e/min)
Stress
(MPa)
Stressinitiation
Stressfailure
0.005a
147 (6.4%)c
0.56 (7.0%)
0.025a
147 (3.9%)
0.56 (0.7%)
0.1a
153 (4.1%)
0.59 (5.0%)
0. 5 b
152 (4.0%)
0.59 (11.6%)
a Data collected for 2 specimens
b Data collected for 3 specimens
c numbers in parentheses are coefficients of variation
-118-
all strain rates tested. Failure initiation in the IM7/977-2 notched panels is
insensitive to strain rates.
The appearances of the failed notched specimens are different at
different strain rates. The failure path at the slowest strain rate is straight
and well defined. As the strain rate increases, the failure path becomes
jagged, accompanied by severe matrix splitting on the outer plies.
Strain rate effects on the IM7/977-2 notched panels are only evident in
the progression of final failure. The difference in failure modes observed is
a post failure initiation phenomenon. Varying strain rates affect the path
at which the final fracture propagates through the specimens and hence
the appearance of the failed specimens. The duration of time for tests
conducted at 0.5 e/min is very short, the panels fail in 1.5 sec. Matrix
splitting on the outer plies that accompanied failure propagation left
strands of material that did not break completely. The strands are lifted
from the surfaces and they continue to hold the panel together. Failure
progression that results in a straight fracture path may be hindered. At
the slower strain rates, failure progresses gradually. There is enough time
for matrix splits to break cleanly and a straight fracture path. to form.
5.2
StrAin Rate JEffc
on AS4W8
necimens
Discussion of results of tests conducted on the AS4/938 unnotched
and notched specimens are presented below.
5.2.1
Unnotched Coupons
The failure stresses obtained for the tape layup and tow placed
unnotched coupons show little sensitivity to strain rates. The average
failure stress of the tape layup unnotched coupons decreases slightly (by
-119-
7%) when the stain rate is increased to 2 elmin. The failure stresses of the
tow placed unnotched coupons show no strain rate sensitivity.
The measured laminate longitudinal moduli and major Poisson's
ratios of the two specimen types are similar and insensitive to strain rate.
Also, these values agree with those calculated from CLPT. Failure modes
of the AS4/938 tape layup and tow placed unnotched specimens are also
similar and insensitive to strain rates.
The stress-strain behavior of the AS4/938 unnotched coupons are
independent of strain rate and manufacturing technique. The progressive
failure model, MCLAM, is used to analyze the failure of the AS4/938
unnotched coupons. The predicted stress-strain behavior is plotted with
those typical of a tape layup and tow placed coupon. This is shown in
Figure 5.4 The model over-predicts the failure strength of the unnotched
coupons. The specimens tested fail at lower stresses and strains. On the
prediction curve, distinct load drops are observed at about 600 MPa and
700 MPa, corresponding to failure of the 450 and 30* plies respectively.
Predicted failure of the 450 plies coincided with final failure of the coupons
tested. This implies that the AS4/938 unnotched coupons did not survive the
failure of the
±45*
plies.
The layup of the AS4/938 specimens is stronger than that of the
IM7/977-2 specimens. The 600 plies are replaced by the 30' plies. Also,
resin type 938 is an untoughened resin. The lack of load drops in the
experimental stress-strain curves of the unnotched AS4/938 coupons
indicates a less progressive type of failure.
The curves behave almost
linearly throughout the loading at all strain rates.
-120-
1000-
AS4/938 Unnotched
S[45/0/90/+30/0]s
Predicted Failure
800Predicted Failure
of +450 plies
600 cn
L.
to
Specimen Failure
400 ---
200 -
Tape Layup
-o--- Tow Placed
,-
Progressive Failure Prediction
!
4000
Figure 5.4
8d00
Strain (pstrain)
12000
Experimental and Predicted Stress-Strain Curves of AS4/938
Unnotched Coupons.
-121-
.2.2
Notched Spedmens
Failure strengths of the AS4/938 tape layup notched specimens show
significant dependency on strain rates while that of the tow placed
specimens show less dependency on strain rates. The average failure
strength of the tape layup specimens with the 19 mm slit decreases by 19%
from the 'static' value at 2 e/min; the average failure strength of the tow
placed specimens shows no significant sensitivity at all strain rates. For
specimens with the 51 mm slit, the average failure strength of the tape
layup panels decreases by 15% from the 'static' value at 2 e/min;
the
average failure strength of the tow placed panels decreases by 9% from the
'static' value at the same strain rate.
The failure strengths of the notched tow placed specimens with both
slit sizes are higher than that for the corresponding tape layup specimens.
This strength advantage is evident at all three strain rates. Tow placed
specimens with the 19 mm slit are stronger than the tape layup specimens
by about 25% at 0.0042 e/min and 0.1 e/min, and about 50% at 2 e/min; tow
placed specimens with the 51 mm slit are stronger than the tape layup
specimens by about 50% at all strain rates.
Strain rate effects on the laminate longitudinal modulus and major
Poisson's ratio of both specimen types are insignificant. Failure modes of
the tape layup notched specimens are different from that of the tow placed
specimens. The fracture path of the tape layup specimens is straight and
relatively smooth.
The failure path in the tow placed specimens is
complicated by delaminations, with each ply failing at a separate location.
This results in a jagged fracture path.
The failure modes for each
specimen type, however, are insensitive to strain rate.
-122-
The elastic responses of the AS4/938 tape layup and tow placed
specimens are similar, and appear to be insensitive to strain rate. The
AS4/948 unnotched coupons of both specimen types show identical stressstrain behavior at all strain rates. Their measured laminate properties are
alike and insensitive to strain rates. The strain distributions of the AS4/938
notched panels of both types are also similar at low loads before the onset of
damage. This elastic behavior is consistent at all strain rates.
Strain gage readings at the notch tip of the AS4/938 coupons and
panels can be used to estimate the load at failure initiation. Strain readings
collected for a typical notched panel are shown in Figure 5.5. Failure is
assumed to initiate when the notch tip strain gage exhibits a major kink or
other non-linear behavior. The average far-field stresses at which failure
initiations occur are tabulated in Table 5.1 and Table 5.2 for the notched
coupons and panels respectively.
The recorded stresses are also
normalized with the failure stresses.
Failure initiation stresses of the notched tape layup coupons and
panels are only slightly lower than those of the tow placed specimens.
These stresses appear to be slightly strain rate sensitive.
The average
failure initiation stress for the tape layup coupons decreases by about 7% at
2 E/min. The average failure initiation stress of the tow placed specimens is
insensitive to strain rate.
Failure initiation stresses are plotted along with the final failure
stresses at different strain rates in Figure 5.6 and Figure 5.7 for the notched
coupons and panels respectively. The distance between the initiation and
final failure stresses indicates the nature of the progressive damage
process for each type of specimen. A small separation indicates a 'brittle'
failure with little load carrying capability beyond failure initiation. A large
-123-
8000
AS4/938 Tape Layup, 51 mm Slit
Tested at: 0.1 e/min
(Specimen M3-LIN12)
6000
Failure Initiation
-4000
t
C2000
2000
ain
Figure 5.5
I
I
0.5
1
1.5
2
Time (sec)
2.5
Strain Readings Collected of Typical IM7/977-2 Notched Panel.
-124-
500400-
AS4/938 Notched, 19 mm Slit
[r45/0/90¥30/0]s
300-
Cd
UD
03
200100- Tape Lavuo Couoons:
00.001
Figure 5.6
Tow Placed Coupons:
Failure Initiation Stress
Failure Initiation Stress
Final Failure Stress
Final Failure Stress
I
0.01
0.1
Strain Rate (s/min)
10
Failure Initiation Stress and Final Failure Stress of AS4/938
Notched Specimens, 19 mm Slit.
-125-
400
AS4/938 Notched, 51 mm Slit
[T45/0/90T30/0]s
300 1a
Ca)
CD)
200 -
0)
L.
100-
0-
Tow Placed Coupons:
Tape Layup Coupons:
Failure Initiation Stress A Failure Initiation Stress
Ol Final FailureStress
Final Failure Stress
0.001
Figure 5.7
I
0.01
I
0.1
Strain Rate (s/min)
10
Failure Initiation Stress and Final Failure Stress of AS4/938
Notched Specimens, 19 mm Slit.
-126-
Average Stress at Failure Initiation and Ratio of Initiation
Stress to Failure Stress for the AS4/938, 19 mm Notched
Table 5.2
Specimens
Strain Rate
(e/min)
Stress
(MPa)
Stressinitiation
Stressfailure
0.0042
214 (1 7 .7 %)b
0.78 (22.0%)
0.1
241 (8.0%)
0.84 (6.96%)
2
198 (10.4%)
0.87 (11.0%)
0.0042
256 (8.1%)
0.73 (10.7%)
0.1
266 (4.8%)
0.72 (10.1%)
2
246 (8.4%)
0.73 (15.4%)
Tape Layupa:
Tow Placementa:
a Data collected for 5 specimens
b numbers in parentheses are coefficients of variation
-127-
Average Stress at Failure Initiation and Ratio of Initiation
Stress to Failure Stress for the AS4/938, 51 mm Notched
Table 5.
aEpeonW"
Strain Rate
(e/min)
Stress
(MPa)
Stressinitiation
Stressfailure
0.0042
134 (7 .2 %)b
0.64 (4.2%)
0.1
130 (16.4%)
0.69 (8.1%)
2
131 (14.8%)
0.69 (0.1%)
0.0042
170 (3.4%)
0.58 (2.0%)
0.1
163 (7.6%)
0.55 (8.3%)
2
171 (0.9%)
0.62 (3.7%)
Tape Layupa:
Tow Placementa:
a Data collected for 2 specimens
b numbers in parentheses are coefficients of variation
-128-
separation indicates a progressive failure.
This may be a result of
redistribution of stresses near the notch tip due to local damage.
Failure progression of the AS4/938 notched specimens appears to be
dependent on both strain rate and manufacturing technique. For both slit
sizes, failure progression is significantly more strain rate sensitive for the
tape layup specimens than the tow placed specimens.
As strain rate
increases, failure progression is hastened in the tape layup specimens. On
the other hand, failure progression of the tow placed specimens is strain
rate insensitive for the slit size of 19 mm and only slightly strain rate
sensitive for the slit size of 51 mm.
The different failure modes observed for both specimen types support
this finding. The fracture path of the tape layup specimen is straight,
implying that the specimen failed through the propagation of a
macrocrack. This type of failure progression is faster at higher strain
rates, resulting in lower failure strengths [43]. The fracture path of the
tow-placed specimens is more jagged and rough. It does not cut through
all the plies at the same location. Different sets of plies have their own
distinct fracture path.
Intuitively, this mode of failure will delay the
progression to failure as higher loads are required to form the different
fracture paths in the specimen.
In Section 4.3.4, the AS4/938 tow placed notched specimens were
shown to have better damage tolerance that the tape layup specimens. This
advantage extends over all three strain rates. As illustrated above, the
failure mechanism for the tow placed and tape layup notched specimens is
different. The AS4/938 tow placed specimens are slightly tougher than the
tape layup specimens at all strain rates tested. This is indicated by the
higher failure initiation stresses required for the tow placed specimens.
-129-
However, once failure begins, the tow placed specimens behave in the
'softer' manner. They are able to redistribute or absorb stresses better than
the tape layup specimens. This finding is consistent with results obtained
by other researchers [46]. They found intraply resin rich zones in the tow
placed specimens that enhance the splitting mechanism along the loading
axis.
The AS4/938 tape layup notched specimens exhibit brittle failure that
is common with graphite/epoxy composite systems. The 'brittleness' of this
material increases with increasing strain rates, resulting in lower failure
strengths. The overall effect on these specimens is a decreasing ability to
tolerate damage as strain rate increases. Previous work on interlaminar
fracture toughness showed strain rate sensitivity in the same regime of
strain rates [40, 41].
In those experiments, the material used was
AS4/3501-6, whose material properties are very similar to that of AS4/938.
However, as mentioned in Section 2.2, the results obtained were
contradictory. Nonetheless, they show that the toughness and damage
mechanism of this type material system are strain rate sensitive. The
results obtained here are consistent, in a general way, with the previous
finding.
-130-
Chapter 6
CONCLUSIONS AND RECOMMENDATIONS
The conclusions and recommendations presented in this chapter are
a result of the experimental work and subsequent analysis conducted in the
course of this investigation and presented in the previous chapters.
6.1
Conclusions
The primary finding of this work is that the damage tolerance and
progressive failure mechanisms of graphite/epoxy laminates are dependent
on strain rate and manufacturing technique.
The elastic behavior of these laminates was not dependent on these
factors. The measured elastic properties and elastic strain distributions
showed no such dependencies.
theories.
They agreed very well with existing
The failure loads of the unflawed specimens also showed no
strain rate or manufacturing technique sensitivities.
In the notched
panels, the load at which evidence of failure was first detected was also only
weakly dependent on these factors.
However, the progression from initial failure to final failure in
notched specimens is clearly strain rate and manufacturing technique
dependent.
Specimens made of a soft layup of toughened IM7/977-2
material showed no sensitivity to strain rate in their final failure loads.
However, the appearance of the failed specimens differed after tests at
different strain rates. This indicates the final progress of the failure after
peak load was reached was strain rate dependent.
-131-
Notched specimens made from a 'harder' layup of AS4/938 material
showed strong dependence of the final failure load on both strain rates and
manufacturing technique. Tape layup specimens acted in a brittle fashion,
failing soon after failure initiation.
This problem worsened at higher
strain rates. The tow placed specimens failed at loads much higher than
the loads at which failure initiated. Their failure appearance gives further
evidence that they failed by a complex, progressive mechanism.
6.2
Recommendations
Further work is already in progress to identify the effects of other
parameters, such as different material systems and layups, on this
problem. It is recommended that materials under consideration for use in
composite aircraft structure (e.g., new toughened matrix composites) be
tested for strain rate sensitivity. It is also recommended that the strain
rates used be adjusted as necessary to reflect realistic loading scenarios.
Work that could contribute to the better understanding of the
mechanisms of progressive damage in composite materials is also
recommended. Specimens partially damaged by loading to a level between
initiation and final failure loads can be inspected to observe the progress of
damage.
The interaction of these mechanisms with other damage
mechanisms such as fatigue and impact should also be studied through
combined tests. Finally, these additional studies should be carried out with
a view of either supporting or disproving proposed damage mechanisms.
The long term goal of this work should be the development of sufficient
understanding of damage mechanisms in composite materials to allow
confident analysis of these materials, and structures made of them.
-132-
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Department of Aeronautics and Astronautics, May 1988
48
Sawicki, A.J., "Damage Tolerance of Integrally Stiffened Composite
Plates and Cylinders", M.I.T. Department of Aeronautics and
Astronautics, Master's Thesis, August 1988.
49
Pemberton, R., "Behavior of Wide Graphite/Epoxy Plates with
Notches", Internal TELAC Document, May 1989.
50
National Instruments, "LabVIEW2 Data Acquisition VI Library
Reference Manual", Part Number 320249-01, September 1991 Edition.
51
Vizzini, A.J., "An Efficient Algorithm to Characterize Stress-Stain
Data Using Piecewise Linear Curves", Journal of Testing and
Evaluation,Vol. 20, No. 2, March 1992, pp. 126-131.
52
Lekhnitskii, S.G., Anisotropic Plates, S.W. Tsai and T. Cheron,
Trans., Gordon and Breach Science Publishers, 1968.
53
Brown, W.F., and Srawley, J.E., "Plane Strain Crack Toughness
Testing of High Strength Metallic Materials", ASTM STP 410,
American Society of Testing and Materials, 1965, pp. 30-83.
-138-
APPENDIX A
Table A.1 IM7/977-2 Unnotched Coupon Parameters
Specimen
Average
Width
[mm]
Average
Thickness
[mm]
Strain Rate
Tested
[e/min]
M1-SUO1
51.1
2.44
0.025
M1-SU02
51.3
2.45
0.025
M1-SUO3
51.4
2.44
0.005
M1-SU04
47.2
2.45
0.005
M1-SU05
51.2
2.45
0.1
M1-SU06
51.6
2.46
0.5
M1-SU07
51.2
2.46
0.5
M1-SU08
47.2
2.46
0.1
-139-
Table A.2 IM7/977-2 Notched Panel Parameters
Specimen
Average
Width
Average
Thickness
Measured
Slit Size
Strain Rate
Tested
[mm]
[mm]
[mm]
[e/min]
M1-LN01
206.0
2.47
50.2
0.005
M1-LN02
206.0
2.43
51.6
0.5
M1-LN03
206.0
2.47
51.4
0.125
M 1-LN04
205.9
2.46
51.7
0.0125a
M1-LN05
205.9
2.49
50.2
0.5
M1-LN06
205.9
2.45
50.8
0.125
M1-LN07
205.1
2.5
52.0
0.025
M1-LN08
205.2
2.48
50.7
0.005
M 1-LN09
205.1
2.46
51.3
0.025
M1-LN10
205.3
2.43
51.7
0.125
M1-LN11
205.2
2.47
50.9
0.005
M1-LN12
205.1
2.47
50.2
0.5
a Incorrect stroke rate used during test
-140-
Table A.3 IM7/977-2 Unnotched Coupon Failure and Stiffness Data
Measured
Strain Rate
[c/min]
Failure
Stress
[MPa]
Failure
Strain
[pstrain]
Laminate
Longitudinal
Modulus
[GPa]
Laminate
Major
Poisson's
Ratio
0.004
579
15720
35.6
0.26
0.004
509
14870
38.5
0.26
0.020
534
16300
39.0
0.26
0.020
586
16390
40.3
0.27
0.08
518
14900
38.2
0.27
0.08
502
15250
37.4
0.27
0.4
572
15300
39.0
0.27
0.4
558
14720
39.2
0.26
-141-
Table A.4 IM7/977-2 Notched Panels Failure Data
Measured
Strain Rate
[e/min]
Failure Stress
[MPa]
Failure Strain
[gpstrain]
0.004
254
5950
0.004
257
6050
0.004
267
6200
0.009 a
262
5960
0.018
259
5910
0.018
260
5650
0.090
266
6140
0.080
256
6200
0.083
263
6070
0.34
246
5910
0.32
260
5880
0.30
269
6010
a Incorrect stroke rate used during test
-142-
APPENDIX B
Table B.1 AS4/938 Tape Layup Unnotched Coupon Parameters
Specimen
Average
Width
[mm]
Average
Thickness
[mm]
M3-SU01
77.0
2.52
0.1
M3-SU02
77.1
2.46
0.0042
M3-SU03
77.1
2.50
0.0042
M3-SU04
77.0
2.47
0.0042
M3-SU05
77.1
2.45
0.0042
M3-SU06
77.1
2.42
0.0042
M3-SU07
77.0
2.43
0.1
M3-SU08
76.7
2.45
0.1
M3-SU09
76.9
2.46
0.1
M3-SU10
77.1
2.46
0.1
M3-SU11
77.1
2.42
2
M3-SU12a
76.9
2.45
2
M3-SU13a
77.1
2.44
2
M3-SU14
77.0
2.45
2
M3-SU15
77.2
2.47
2
M3-SU16
76.7
2.44
2
M3-SU17
76.8
2.44
2
a Data lost during test
-143-
Strain Rate
Tested
[e/min]
Table B.2 AS4/938 Tow Placed Unnotched Coupon Parameters
Specimen
Average
Width
[mm]
Average
Thickness
[mm]
M2-SU01
76.3
2.52
0.0042
M2-SU02
76.1
2.53
0.1
M2-SU03
76.2
2.53
0.1
M2-SU04
76.2
2.42
2
M2-SU05
76.1
2.52
0.0042
M2-SU06
76.1
2.52
0.0042
M2-SU07
76.1
2.52
0.0042
M2-SU08
76.1
2.52
0.1
M2-SU09
77.3
2.51
0.1
M2-SU10
77.4
2.52
2
M2-SU11
76.1
2.52
2
M2-SU12
76.1
2.50
2
M2-SU13
76.9
2.52
0.1
M2-SU14
76.2
2.51
0.0042
M2-SU15
76.2
2.53
2
-144-
Strain Rate
Tested
[e/min]
Table B.3 AS4/938 Tape Layup Notched Coupon Parameters
Specimen
Average
Width
Average
Thickness
Measured
Slit Size
Strain Rate
Tested
[mm]
[mm]
[mm]
[e/min]
M3-SNO1
76.9
2.48
-a
0.0042
M3-SN02
77.1
2.45
19.1
0.0042
M3-SN03
77.1
2.43
18.8
0.0042
M3-SN04
77.1
2.46
17.7
0.0042
M3-SN05
76.9
2.44
18.6
0.0042
M3-SN06
77.2
2.45
18.9
0.1
M3-SN07
77.1
2.47
18.2
0.1
M3-SN08
76.7
2.44
17.9
0.1
M3-SN09
77.2
2.44
19.2
0.1
M3-SN10
77.1
2.44
18.6
2
M3-SN11
77.1
2.39
19.1
2
M3-SN12
77.0
2.47
18.8
2
M3-SN13b
77.0
2.48
18.6
2
M3-SN14
77.1
2.48
17.9
2
M3-SN15
76.9
2.38
17.5
2
M3-SN16
76.4
2.40
19.1
0.1
a Slit size not measured prior to test
b Data lost during test
-145-
Table B.4 AS4/938 Tow Placed Notched Coupon Parameters
Specimen
Average
Width
Average
Thickness
Measured
Slit Size
Strain Rate
Tested
[mm]
[mm]
[mm]
[C/min]
M2-SNO1
76.4
2.52
19.4
0.0042
M2-SNO2
76.2
2.54
18.6
2
M2-SN03
76.2
2.55
19.8
0.1
M2-SN04
76.1
2.52
19.1
2
M2-SN05
76.1
2.51
21.2
0.0042
M2-SN06
77.4
2.51
19.0
0.1
M2-SN07
76.1
2.52
20.1
0.1
M2-SN08
76.1
2.49
19.1
0.0042
M2-SN09
76.1
2.50
19.7
2
M2-SN10
76.1
2.51
19.2
0.1
M2-SN11
76.1
2.51
19.8
0.0042
M2-SN12
77.4
2.51
19.9
2
M2-SN13
76.1
2.51
19.6
0.1
M2-SN14
75.9
2.52
19.1
0.0042
M2-SN15
76.0
2.51
19.1
2
-146-
Table B.5 AS4/938 Tape Layup Notched Panel Parameters
Specimen
Average
Width
[mm]
Average
Thickness
[mm]
Measured
Slit Size
[mm]
M3-LN01
204.3
2.43
50.9
2
M3-LN03
204.4
2.46
50.5
0.1
M3-LN04
204.4
2.44
-a
0.0042
M3-LN05
204.6
2.47
51.4
0.0042
M3-LNO6
204.8
2.41
50.7
0.1
M3-LN07
204.6
2.46
50.9
2
M3-LN08
204.8
2.46
51.0
0.1
M3-LN09
204.8
2.42
50.5
0.0042
M3-LN10
204.8
2.47
50.6
2
M3-LN11
204.9
2.47
48.3
2
M3-LN12
204.3
2.42
51.1
0.1
M3-LN13
205.0
2.43
51.4
0.0042
M3-LN14
203.7
2.43
50.2
2
M3-LN15
204.4
2.43
50.2
0.0042
M3-LN16
204.7
2.40
51.1
0.1
a Slit size not measured prior to test
-147-
Strain Rate
Tested
[e/min]
Table B.6 AS4/938 Tow Placed Notched Panel Parameters
Specimen
Average
Width
[mm]
Average
Thickness
[mm]
Measured
Slit Size
[mm]
Strain Rate
Tested
[e/min]
M2-LN01
203.2
2.52
50.6
0.0042
M2-LN02
203.3
2.50
50.4
2
M2-LN03
203.3
2.46
51.7
0.0042
M2-LN04
205.5
2.50
50.8
0.1
M2-LN05
203.6
2.52
50.8
0.0042
M2-LNO6
203.6
2.53
51.7
2
M2-LN07
204.1
2.51
50.8
0.0042
M2-LN08
203.7
2.53
50.8
0.1
M2-LN09
204.0
2.51
50.9
0.1
M2-LN10
203.6
2.52
50.9
0.0042
M2-LN11
204.0
2.53
50.8
2
M2-LN12
203.8
2.50
51.3
2
M2-LN13
204.2
2.51
51.3
0.1
M2-LN14
204.4
2.52
50.9
2
M2-LN15
204.1
2.52
51.1
0.1
-148-
Table B.7 AS4/938 Tape Layup Unnotched Coupon Failure and Stiffness
Measured
Strain Rate
[e/min]
Failure
Stress
[MPa]
Failure
Strain
[gstrain]
0.003
634
0.003
Data
Laminate
Longitudinal
Modulus
[GPa]
Laminate
Major
Poisson's
Ratio
10540
61.2
0.48
614
10170
61.3
0.48
0.003
589
9850
60.6
0.49
0.003
631
9970
62.9
0.46
0.003
572
10054
57.6
0.49
0.084
606
10280
58.9
0.45
0.084
575
10150
56.8
0.48
0.080
585
9880
60.8
0.48
0.082
612
10040
61.0
0.46
0.079
610
10010
60.6
0.47
1.51
525
9260
57.6
0.52
1.51
577
9680
63.1
0.50
1.47
568
9320
62.6
0.50
1.47
563
9480
61.6
0.49
1.53
592
9590
63.4
0.48
-149-
Table B.8 AS4/938 Tow Placed Unnotched Coupon Failure and Stiffness Data
Measured
Strain Rate
[e/min]
Failure
Stress
[MPa]
Failure
Strain
[gstrain]
Laminate
Longitudinal
Modulus
[GPal
Laminate
Major
Poisson's
Ratio
0.003
589
10410
60.6
0.48
0.003
614
10450
62.1
0.47
0.003
574
9450
60.7
0.52
0.003
584
10240
59.0
0.44
0.003
585
9783
60.5
0.50
0.079
602
9760
63.1
0.53
0.080
619
10090
63.9
0.54
0.080
606
10120
60.6
0.49
0.081
588
9750
62.1
0.47
0.083
612
10210
61.5
0.51
1.42
579
9090
65.7
0.52
1.45
584
9720
62.0
0.47
1.43
589
9750
61.6
0.49
1.46
578
9590
60.4
0.49
1.51
579
9920
59.6
0.46
-150-
Table B.9 AS4/938 Tape Layup Notched Specimens Failure Data
Notched Coupon
(19mm Slit)
Notched Panel
(50.8mm Slit)
Measured
Strain
Rate
[e/min]
Failure
Stress
[MPa]
Failure
Strain
[Astrain]
Measured
Strain
Rate
[emin]
Failure
Stress
[MPa]
Failure
Strain
[jistrain]
0.003
294
4600
0.003
213
2890
0.003
256
4000
0.003
204
2664
0.003
255
3320
0.003
206
3180
0.003
302
4440
0.003
188
2800
0.003
287
4770
0.003
174
2640
0.074
243
4040
0.068
200
2880
0.076
291
4300
0.067
204
3100
0.075
305
4700
0.069
168
2597
0.073
265
4110
0.068
199
2760
0.072
333
4820
0.068
176
2590
1.31
257
3840
1.07
170
2460
1.30
211
3210
1.13
142
2300
1.30
226
3390
1.09
210
3080
1.30
221
3290
1.16
173
2630
1.35
221
3510
1.15
143
2050
-151-
Table B.10 AS4/938 Tow Placed Notched Specimens Failure Data
Notched Coupon
(19mm Slit)
Notched Panel
(51mm Slit)
Measured
Strain
Rate
[e/min]
Failure
Stress
[MPa]
Failure
Strain
[gstrain]
Measured
Strain
Rate
[e/min]
Failure
Stress
[MPa]
Failure
Strain
[listrain]
0.003
354
5290
0.003
274
4010
0.003
359
4760
0.003
292
4320
0.003
343
5190
0.003
298
3880
0.003
336
5000
0.003
297
4130
0.003
362
5200
0.004
288
4030
0.074
411
5860
0.064
294
3760
0.073
398
5530
0.071
297
4470
0.074
349
5120
0.068
298
4090
0.074
350
5030
0.068
301
4360
0.073
341
5140
0.071
273
3650
1.30
343
5280
1.13
266
3640
1.26
357
4680
1.09
280
3720
1.20
297
3600
1.14
283
3970
1.33
353
5320
1.20
259
3800
1.34
345
5120
1.20
226
3380
-152-
APPENDIX C
I
AS4/938 Tape Layup
Strain Rate = 0.0042 E/min
LC
Specimen Designation: M3-LN04
2.5-
30% Load
0 50% Load
O 80% Load
•Prediction
A
I
ULL
2-
L.
1.50
0
.1
I
I
iI
-I
15
30
45
60
Distance from Tip of Notch (mm)
Figure C.1
75
Strain Distribution of AS4/938 Tape Layup Notched Specimen
M3-LN04 at 0.0042 e/min.
-153-
AS4/938 Tape Layup
Strain Rate = 0.0042 E/min
C
t-
Specimen Designation: M3-LN05
A
20% Load
o 50% Load
O 80% Load
Prediction
c- 2LL
L..
- 1.5I
O
1
0
Figure C.2
I
i
I
I
15
30
45
60
Distance from Tip of Notch (mm)
75
Strain Distribution of AS4/938 Tape Layup Notched Specimen
M3-LN05 at 0.0042 e/min.
-154-
0
AS4/938 Tow Placement
Strain Rate = 0.0042 E/min
C01c
Specimen Designation: M2-LN03
2.5-D
-
A
0
_0
CD
20% Load
50% Load
>O80% Load
SPrediction
-J2-
LL.
C
Ii
-1.5I
O
O
1
1-
0
Figure C.3
I
I
I
I
I
I
I
15
30
45
60
Distance from Tip of Notch (mm)
75
Strain Distribution of AS4/938 Tow Placed Notched Specimen
M2-LN03 at 0.0042 /min.
-155-
m
Q-
AS4/938 Tow Placement
Strain Rate = 0.0042 E/min
c
Specimen Designation: M2-LN05
2.5-
30% Load
O 50% Load
O 80% Load
- Prediction
A
UI
c 2LL
-C
1.5-
-
O
1
0
Figure CA.4
15
30
45
60
Distance from Tip of Notch (mm)
75
Strain Distribution of AS4/938 Tow Placed Notched Specimen
M2-LN05 at 0.0042 E/min.
-156-
%F-
AS4/938 Tape Layup
Strain Rate = 0.1 &/min
Specimen Designation: M3-LN12
-o
S2.5-
A
20% Load
o 50% Load
O 80% Load
Cz
,_
LL.
Prediction
2-
t-
1.50
0
1J
1-
0
Figure C.5
I
I
I
I
15
30
45
60
Distance from Tip of Notch (mm)
75
Strain Distribution of AS4/938 Tape Layup Notched Specimen
M3-LN12 at 0.1 e/min.
-157-
AS4/938 Tape Layup
Strain Rate = 0.1 e/min
CD
Specimen Designation: M3-LN16
A
20% Load
o 50% Load
O 80% Load
L..
Prediction
2n
1.5-
CO
LL.-J
7
1-
0
Figure C.6
60
45
30
15
Distance from Tip of Notch (mm)
75
Strain Distribution of AS4/938 Tape Layup Notched Specimen
M3-LN16 at 0.1 c/min.
-158-
.0
,J
AS4/938 Tow Placement
Strain Rate = 0.1 E/min
C
Specimen Designation: M2-LN04
-e
A 30% Load
0 50% Load
O 80% Load
Prediction
S2.5"O
-0
CO_2t-
1.5I
I
1-
0
Figure C.7
60
45
30
15
Distance from Tip of Notch (mm)
I
75
Strain Distribution of AS4/938 Tow Placed Notched Specimen
M2-LN04 at 0.1 e/min.
-159-
AS4/938 Tow Placement
Strain Rate = 0.1 d/min
Specimen Designation: M2-LN08
A
O 50% Load
U)
cat-
20% Load
O 80% Load
-
2-
Prediction
0O
0-
-A
1-
0
Figure C.8
I
I
I
I
60
45
30
15
Distance from Tip of Notch (mm)
75
Strain Distribution of AS4/938 Tow Placed Notched Specimen
M2-LN08 at 0.1 e/min.
-160-
AS4/938 Tape Layup
--
Strain Rate = 2 E/min
-
Specimen Designation: M3-LN01
A
20% Load
0 50% Load
O 80% Load
Prediction
-_
LL
A
C- 1.5Ca
t-
O
10
Figure C.9
I
I
I
I
60
45
30
15
Distance from Tip of Notch (mm)
75
Strain Distribution of AS4/938 Tape Layup Notched Specimen
M3-LN01 at 2 emin.
-161-
.9
AS4/938 Tape Layup
Strain Rate = 2 e/min
Specimen Designation: M3-LN10
S2.5-
A
U)
o 50% Load
O 80% Load
Prediction
4--
2-
30% Load
A
o
0
10
Figure C.10
I
I
I
I
15
30
45
60
Distance from Tip of Notch (mm)
75
Strain Distribution of AS4/938 Tape Layup Notched Specimen
M3-LN10 at 2 /min.
-162-
a
AS4/938 Tow Placement
Strain Rate = 2 e/min
t-
Specimen Designation: M2-LN02
A
cu
LL
LL
O 50% Load
O 80% Load
•- Prediction
1-
I
30% Load
22.5-
t.-
"
1
-A
0
'I
I0
30
45
1-
0
15
60
75
Distance from Tip of Notch (mm)
Figure C.11
Strain Distribution of AS4/938 Tow Placed Notched Specimen
M2-LN02 at 2 e/min.
-163-
AS4/938 Tow Placement
Strain Rate = 2 d/min
Specimen Designation: M2-LN11
2.5
A
c)
U-
30% Load
O 50% Load
O 80% Load
Prediction
2
C
0
1.5r
IIA
.J0
I
III
I6
30
60
15
Distance from Tip of Notch (mm)
Figure C.12
I
75
Strain Distribution of AS4/938 Tow Placed Notched Specimen
M2-LN11 at 2 e/min.
-164-
APPENDIX D
80 IM7/977-2, Unnotched
Specimen M1-SU01
Strain Rate: 0.025 E/min
60
,
C,)
-o
40-
3
0
-j
3
20
---- Load
1
----- Stroke
U
0
20000
I
|
10
20
I
I
|
•
|
50
30 40
Time (sec)
|
60
0
70"
-5000
IM7/977-2, Unnotched
Specimen M1-SU01
Strain Rate: 0.025 E/min
-4000 m
15000
cn
-3000 2
co 10000
-2000 2
"5 5000
------
0
Figure D.1
!
0
I
10
I
20
I
30
40
Time (sec)
Longi tudinal Strain 1 -1000
Transverse Strain
I
5(0
I
60
-n
70
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M1-SU01.
-165-
6
•A
- -·
O0v
IM7/977-2, Unnotched
Rrb.cimAn M1- StIn2
Si
5
60
V
3
400
-J
I
20)ad
1
rk
roke
,
0
I
10
20000
20
I
I
40
30
Time (sec)
1
1
50
60
0n
70
-5000
IM7/977-2, Unnotched
Specimen M1-SU02
Strain Rate: 0.025 e/l
-I
-4000 m
15000
CD
C
U-.
-3000
b10000
-2000 "
'Ic
C 5000
-----
Longitudinal Strain
-1000
--0- Transverse Strain
0.
0
Figure D.2
I
!
50
60
W
10
20
40
30
Time (sec)
I
_n
70
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M1-SU02.
-166-
~
80 IM7/977-2, Unnotched
Specimen M1-SU03
FCI~A. fn1
1 lmn
C%.0%;@
3LI
"
Y
4
5
60
4IC 40
0o
-J
3
cc
20
- Load
drmL
n
|
(V
0
20000.
50
I
I
I
Ir
i
i
100
I
I
150 200 250 300
Time (sec)
An
356
-5000
IM7/977-2, Unnotched
Specimen M1-SU03
Strain Rate: 0.005 e/min
C
1
- .~trno
•I V·Ir\
-4000
15000
D-3000
-3000
0 10000
CD
-i
-2000
" 5000
0
-J
n
v
i
I
0
Figure D.3
- a- Longitudinal Strain
--i- Transverse Strain
I
I
50
100
t
I
!
150 200 250
Time (sec)
I
300
-1000 ,
I'
* -1
350
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M1-SU03.
-167-
80 IM7/977-2, Unnotched
Specimen M1-SU04
Strain Rate: 0.005 e/min
60
7
Ch
I
-o
40W 40
-J
3
3
20
-
-*-
Load
w
Stroke
I
C
)
50
100
150
200
I
250 300
n
356
Time (sec)
"Annnn
-5000
IM7/977-2, Unnotched
Specimen M1-SU04
Strain Rate: 0.005 e/m
.
-4000 0
7
15000
,
-3000 9
5 10000
ad
-2000
S5000
3O
Figure D.4
0
---|
v
0
50
I
|
100
---
Longitudinal Strain -
--
Transverse Strain
I
I
I
150 200 250
Time (sec)
I
300
-1000 3
.-n
350
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M1-SU04.
-168-
"
80 IM7/977-2, Unnotched
Specimen M1-SU05
Strain Rate: 0.1 E/min
60
5
4(n
-o 40
30
3
0
20
ad
7
xlý
)ke
I
I
5
20000
1..
23
1
·
·
Time (sec)
10
A
15.
-5000
IM7/977-2, Unnotchec
Specimen M1-SU05
Strain Rate: 0.1 e/min
-4000 0
15000
Cr
1..
C
-3000
10000-2000 5
4.d
Cr
0D
CD
5000
-- *
-1000 zr
Longitudinal Strain
--0- Transverse Strain
I
I
-
Time (sec)
Figure D.5
10
-1
115
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M1-SU05.
-169-
80 IM7/977-2, Unnotched
Specimen M1-SU05
S
60
1
5
0)
3
40
-o
%fwo
3
2
20
-4- Load
1
---- Stroke
0 I
v
·
I
·
1
2
3
/0
Time (sec)
20000
-C•,-
-5000
IM7/977-2, Unnotched
Specimen M1-SU06
Strain Rate: 0.5 e/min
--I
-4000 0
15000
CD
-3000 '
C 10000
-2000 '
'
5000
C
0
Figure D.6
ft.
V
---
Longitudinal Strain
-1000 -
--0-- Transverse Strain
2
Time (sec)
I-0
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M1-SU06.
-170-
80 IM7/977-2, Unnotched
Specimen M1-SU07
Strain Rate: 0.5 E/min
5
604 -9
o
-Id
40
3
CD
0
20
Load
-
I
I
|
*
0
2A0000
1
2
Time (sec)
1
Stroke
m
|
|
33
3
0
4
-
IM7/977-2, Unnotched
Specimen M1-SU07
Strain Rate: 0.5 e/min
--I
-4000 m
-
CD
C
-.
i;15000
-3000 2
(n
-
-2000
c
C5
-o 10000
" 5000
---
-1000
Longitudinal Strain
--0- Transverse Strain
0
0
Figure D.7
1
·
-I
2
Time (sec)
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M1-SU07.
-171-
80
IM7/977-2, Unnotched
Specimen M1-SU08
Strain Rate: 0.1 e/min
MI
a
BD
40
i
%oo
'0c
9
20
U
J
'1'
I
-+-
Load
----
Stroke
I
i
I
0n
15
10
Time (sec)
20000.
-
-
IM7/977-2, Unnotched
Specimen M1-SU08
Strain Rate: 0.1 emin
-
-
-DUUU
-5
-
.-4000 0
15000.
-30002
L.M
C'
-2000
50000
0 o
0.
+--- Longitudinal Strain
-FJ- Transverse Strain
'
-
I
I
Time (sec)
Figure D.8
-1000
I
10
I
-n
15
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M1-SU08.
-172-
140
120
5
100
4o
- 80
3
S60
3
40
20
1
n
n
v
30
20000
60
90
Time (sec)
120
156
120
150
IM7/977-2, 51 mm Slit
Specimen M1-LN01
Tested at: 0.005 e/min
"•15000
5
10000,
LL
Y 00
CO
CD
eU
I
0ý
C
Figure D.9
30
·
60
90
Time (sec)
Plots of Load, Stroke and Far-Field Strain versus Time for
Specimen M1-LNO1.
-173-
6
140-
IM7/977-2, 51Imm Slit
L-KIND
Specimen
120 Strain Rate:M1
0.5 elmin
100
5
-
4cn
80
3
zOOOW
Ae
60
E
40
--- Load
20
Stroke
I
n
_
_I
1
_
_
_
_
_
_
I
0.5
0
2000C
1
Time (sec)
1.5
n
2
.·
Slit
II
MI
I
mm
51
7/977-2
Specimen M1-LNO2
Tested at: 0.5 s/min
15000.
C
10000.
5000
--a- Far-Fie Id Strain
0J
r
Figure D.10
0
0.5
I
I
-0- Notch- Tip Strain
Time (sec)
I
1.5
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M1-LNO2.
-174-
1~
~IA
14U
IM7/977-2, 51 mm Slit
Ml-LNO3
120 _Specimen
Strain Rate: 0.1 E/min
5
100
-
0
80
o
9 60
2'
40oad
20
E
n
0
1
troke
I
I
1
2
I
4
3
Time (sec)
I
5
03
6
C
"E"
COC
C)
Time (sec)
Figure D.11
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M1-LNO3.
-175-
.1-
A
140
0
120
5
100
4 co
%80
3
q 60
3
40
20
010
030
40
560"
n
0
10
20
30
40
Time (sec)
50
60
onnnf
IM7/977-2, 51 mm Slit
Specimen M1-LN04
Tested at: 0.01 e/min
15000
10000
U.
.
c 5000
I.
0
0
Figure D.12
I
10
I
20
I
I
30
40
Time (sec)
I
50
60
Plots of Load, Stroke and Far-Field Strain versus Time for
Specimen M1-LN04.
-176-
140°
6
IM7/977-2, 51 mm Slit
M1-LN05
120 .Specimen
Strain Rate
100.
5
40
-,
s80o
3
S60
2
40-
20-
P/
--
Load
--
Stroke
KL
--
0.5
1
Time (sec)
1.5
1
A
2V
2
C
LM
C
CD
Time (sec)
Figure D.13
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M1-LNO5.
-177-
140
120-
5
100
40
S80
3
0 60
2
40
1
20
04
1
20000
1M
3
2
3
4
Time (sec)
5
n
6
IM7/977-2, 51 mm Slit
Specimen M1-LNO6
Tested at: 0.1•/min
15000.
10000.
LM
LL
5000.
I
_
.
2
..
_
I
3
Time (sec)
Figure D.14
Plots of Load, Stroke and Far-Field Strain versus Time for
Specimen M1-LNO6.
-178-
140
IM7/977-2, 51 mm Slit
Specimen M1-LN07
Strain Rate: 0.025 e/min
120
5
100
zCU
80
4-
3
0
60
-
3
3
40
Load
20
0
1
Stroke
0
i
0
I
i
I
0
5
10
15
20
Time (sec)
25
%3
0
5
10
20
15
Time (sec)
25
30
5/
0%
2000
1500
C
- 1000
C 500
500
Figure D.15
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M1-LN07.
-179-
140
IM7/977-2, 51 mm Slit
Specimen M1-LN08
120 Strain Rate: 0.005 e/min
ZAý
100
5
4 0
V
0
-J
80
30
_ýC
60
3
3
40
oad
20
n
7
troke
w
y
I
r
I
1
I
A
0
30
60
90
Time (sec)
120
156
0
30
90
60
Time (sec)
120
150
C
C
C1
u,
Figure D.16
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M1-LN08.
-180-
140
IM7/977-2, 51 mm Slit
M1-LNO9
120 -Specimen
Strain Rate: 0.025 E/min
5
100
4
80
3 CD
3
-0 o60
2
40
Load
20
0
I
"
0
V•
I
·
I
ir
1
5
10
I
1
otrnke
•W•V
A
I
t
I
15
20
Time (sec)
T
25
3
0
tC
C
Cn
Time (sec)
Figure D.17
0
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M1-LNO9.
-181-
140-
IM7/977-2. 51 mm Slit
M1
120- Specimen
Strain Rate: 0
100. i
5
_
40
%80
3
960
40-#-- Load
20-
--
·
I
0
i
2
3
4
Time (sec)
1
Stroke
5
n
16
2000
1500
%-1000
C5
500
Time (sec)
Figure D.18
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M1-LN10.
-182-
•1
JA
14U
120
5
100
40
zS80
3
- S60
o
3
40
1
20
A
0
30
90
60
Time (sec)
120
Al
156
2000
1500
1000
50
500
0
Figure D.19
30
-A
Far-Field Strain
---
Notch-Tip Strain
60
90
Time (sec)
120
150
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M1-LN11.
-183-
140
IM7/977-2, 51 mm Slit
Specimen
120 Strain Rate:M1-LN12
0.5 E/min
.5
100
.4 co
0
-32XP
.23
_ 80
0 601
3
40
----
20
y
Load
rl
-r-Stroke
I
0.5
·
·
1
1.5
Time (sec)
P.
20000
15000
C-
10000
5000
0
Time (sec)
Figure D.20
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M1-LN12.
-184-
APPENDIX E
120 I
3
Unnotched
AS4/938 Tape Layup,
Specimen M3-SU 01
7/
1001- Strain
2.5
2 mn
80.
-o
72 60
1.50
3
-
-9
1
40
I nirI
20
- Stroke
0.5
·
'
Stroke
-
·
I
~·
·
i
4
Time
10
6
(sec)
AI1I
12000
-tbUUU
AS4/938 Ta pe Layup, Unnotched
Soecimen M3-SU01
Stan Rate:
a 0.1 e/min
.C10000 Strain
-5000
8000
-4000
&5 6000
-3000
C
4000
-20007
Longitudirial Strain
--E- Transvers e Strain
---
9 2000
I
I
4
6
Time (sec)
Figure E.1
I
I
-100032
2
.-
10
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M3-SUO1.
-185-
120
I
AS4/938 Tape Layup, Unnotched
Specimen M3-SU02
2.5
1001 Strain Rate: 0.0042 E/min
2 2
80-
1.5
-o 60o
0
-Jr
40----
20-
Load
0.5
-- n--- Stroke
I
n
I.
C)
12000
. 10000
C
L-
30
60
I
I
-
120 150
90
Time (sec)
'
e
0
216
180
-6000
AS4/938 Tape Layup, Unnotched
Specimen M3-SU02
- Strain Rate: 0.0042 U/n
-5000o-C
8000
-4000
CD
&4 6000
-3000
C
,-
O
M
-2000"
4000
---
2000
Longitudinal Strain
--0-- Transverse Strain
0
Figure E.2
0
I
I
30
60
I
I
90 120 150
Time (sec)
I
180
-1000
-n
210
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M3-SU02.
-186-
120°
AS4/938 Tape Layup, Unnotched
Specimen M3-SU03
2.5
100. - Strain Rate: 0.0042 e/min
- Sta
2 c
80-o
-J
0
60
40
-- +- Load
20
-I
m
12000
I
I
30
60
1
t
I
90 120 150
Time (sec)
-0.5
e
StroI
S8
I
21
180
-6000
AS4/938 Tape Layup, Unnotched
Specimen M3-SU03
~10000
-Strain
-5000
Rate: 0.0042 e/min
C,
8000
-4000 ID
&D6000.
r
-3000
-
C
-2000 "
4000,
C
2000
-,
.j 2000.
,-- Longitudinal Stra in
-1000 ,
--0- Transverse Strai n
i
0
Figure E.3
_
I
30
60
It
·
Iogtuia
·
·
It
90 120 150
Time (sec)
__
180
-A
210
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M3-SU03.
-187-
120
AS4/938 Tape Layup, Unnotched
specime
2.5
100 - Strain Rc
-J
80-
2
60
1.5
40
°
1
Oat.
-4 -- Load
20
Stroke
i
12000
C
I|
I
I
I
I
30
60
90
120
150
Time (sec)
N
180
.ZtrninianrS
VlIIIDI
-5000
n 11 4A92 clmin
' --
V·VV'-.
lIIY
216
-6000
AS4/938 Tape Layup, Unnotched
Specimen M3-SU04
10000
0.5
8000
-*1
-40009
e-
C5 6000
-3000 r=
*= 4000
-2000.
--a Longitudinal Strain
--0- Transverse Strain
9 2000
0
Figure E.4
I
I
I
30
60
I
i
I
90 120 150
Time (sec)
I
-100020
.-
180
210
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M3-SU04.
-188-
120
AS4/938 Tape Layup, Unnotched
Specimen M3-SU05
2.5
100. - Strain Rate: 0.0042 E/min
80
2 0
60
1.5;
z-o
CU
2
2
40
---- Load
-A-- Stroke
20
0
12000
.•10000
0
30
90 120 150
Time (sec)
60
180
0.5
8
21
.-
'*
AS4/938 Tape Layup, Unnotched
Specimen M3-SU05
-6000
-5000
- Strain Rate: 0.0042 e/min
C,
8000
-4000
U5 6000
-3000
4000
-2000
0
L--
-a- Longitudinal Strain
o 2000
I
I II
30
Figure E.5
60
-1000 •
--0- Transverse
Strainn
I
I
90 120
Time (sec)
150
|
180
-0
21 0
.
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M3-SU05.
-189-
"
120-
3
AS4/938 Tape Layup, Unnotched
Q_ reimn EA-.lu InA
Vp
I
2.5
100. Strain F
•i.
_J
li
i l
80
2g
60-
1.50
404
20
-LUdU
0.5
-- Stroke
0
n
)
12000.
10000
90 120 150
Time (sec)
60
30
180
-6000
AS4/938 Tape Layup, Unnotched
Specimen M3-SU06
AAk d'r
-
,
A
1
-9
-5000
.
/
:
n
216
0.0042
Rate
iartS
8000.
-4000
&O6000.
-3000
-2000
4000'
3 2000.
--
Longitudinal Strain
-10002-
---0- Transverse Strain
0
Figure E.6
0
I
0
30
60
,-
I
90 120 150
Time (sec)
180
210
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M3-SU06.
-190-
120-
3
AS4/938 Tape Layup, Unnotched
Specimen M3-SUI
/
100. - Str
2.5
2
80
0
960
0n
1.5
-Id
-
-
40
- Load
20
Stroke
iI
n
0
12000
4
6
Time (sec)
AS4/938 Tap Layup, Unnotched
Specimen M3-SU07
.c 10000
0.5
Strain Rate: 0.1 e/min
-
A
10
-6000
-5000 -I
8000
-4000
5 6000
-3000
* 4000
-2000.
o, 2000
A-- Longitudilnal Strain
.
-10005'
--0- Transven se Strain
.-
4
6
Time (sec)
110
Figure E.7 Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M3-SU07.
-191-
D
120100.
3
AS4/938 Tape Layup, Unnotched
Specimen M3-SU08
/
2.5
- Strain
80
2
60
1.5
40
1 0
D
z
0,
o
- Load
20
0.5
- Stroke
n
II
I
_.I
)
VC I
12000
.c10000
C
II
2
II
4
I
6
8
Time (sec)
-6000
AS4/938 Tape Layup, Unnotched
Specimen M3-SU08
•=_-
•
r•
,A
l
Strain Rat: u.
0
10V
:
-5000 N
/min
8000
-4000
'a
5 6000
-3000 _
C
*
4000
0, 2000
-2000
Longitudi ial Strain
S-*-&-
Transvers;e Strain
-0I•
I•
II
4
6
Time (sec)
Figure E.8
-1000.-
I
I
.-n
10
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M3-SU08.
-192-
120-
3
AS4/938 Tape Layup, Unnotched/
Specimen M3-SU09
100' - Strain I
2.5
r
80
2
02
-o
9I
-19
1
40
/
-A
20
O
I
2
0
12000
-Load
SStroke
n
I
i
4
6
Time (sec)
8
10
-6000
AS4/938 Tape Layup, Unnotched
Specimen M3-SU09
S10000
0.5
7
- Strain Rate: 0.1 e/min
-5000
I-
CO
8000
-4000
05 6000
-3000
-9 4000
-2000
C
o 2000
LUO--I•C
.
Figure E.9
>~7I
I
2
linal
Oira•n
-100050
Transverse Strain
-0-
0
J;..•--I £'• &.,,.= ".=
4
6
Time (sec)
i
-n
110
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M3-SU09.
-193-
120-
3
AS4/938 Tape Layup, Unnotched
Specimen M3-SUl0
2.5
100 - Strain
2
80
-i
1.50
3
o 60
40
-
t
-Load
-Stroke
20
I
I
nL
12000
.%10000
|
1:1
0.5
A
|
2
4
6
Time (sec)
8
10
-6000
AS4/938 Tape Layup, Unnotched
Specimen M3-SU10
- Cornin
VLI
F~III
I
ns
ICIL~·
nA
c/min
ei
-5000
8000
-4000 1
CO 6000
-
4000
3
2000
-3000 %
-2000'
-A-
Longitucdinal Strain
-
-1000o
,-0--Transve'rse Strain
|
2
Figure E.10
4
6
Time (sec)
i _n
A
10
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M3-SU10.
-194-
120
3
AS4/938 Tape Layup, Unnotched
Specimen M3-SU1 1
2.5
100 - Strain Rate: 2 E/min
2 co
80z
1.50
Ca 60
3
3
0
.j
v
40
-Load
20
0.5
-- Stroke
py
----
I
|
0.1
12000
I
|
|
0.3
0.2
Time (sec)
-I'U
r I1|
|
0.4
0.5f
-6000
AS4/938 Tape Layup, Unnotched
Specimen M3-SU1 1
c 10000 - Strain Rate: 2 e/min
-5000
:3
8000
-4000 (
"5 6000
J
4000
0
2000
-3000
-20007
ial Strain
-
-1000
- Transverse Strain
I
0.1
Figure E.11
Co
I
0.2
0.3
Time (sec)
.-n
0.4
0.5
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M3-SU11.
-195-
120°
AS4/938 r·Tape
Layup, Unnotched
a
oI
oplcLlll I
2.5
100. Strain Ra
-
801.5'
-o60o
40-
1
)ad
20
Se
A
v
12000
3
3
__
·
0.1
I
--
·
s- Stroke
·
0.2
0.3
Time (sec)
0.4
0.5
1n
0.O
-6000
AS4/938 Tape Layup, Unnotched
Specimen M3-SU1 4
10000 - Strain Rate: 2e/min
-5000oo
8000
-4000N
6000
()
-3000oo
4000
-2000
Cr
Cr
0n
-J
--a- Longitudinal Strain
-- ]- Transverse Strain
2000
'I
0.1
Figure E.12
t
0.2
0.3
Time (sec)
0.4
-1000ooo
I
I- I I
0.5
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M3-SU14.
-196-
120
AS4/938 Tape Layup, Unnotched
SRncarimen Mq-l91i11
100
-Strain Rate
2.5
2 c
80,
-Y60I
40
ad
20
0.5
Stroke
0
v
i
I
•i
0.1
I
0.3I
0.2
Time (sec)
0.4
120nnn
1
C
L.
r-'
C
-6000
AS4/938 Tape Layup, Unnotched
Specimen M3-SU15
-5000 -I
10000. - Strain Rate: 2 E/min
8000.
-4000
05 6000.
3C
Cr
0)
'I
0.5
-3000 1
4000.
-2000=
Longitudinal Strain
-*-
2000.
-10005,
-0-• Transverse Strain
Figure E.13
I
I
i
i
•
0.1
0.2
0.3
I
Time (sec)
I
•
0.4
-n
0.5
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M3-SU15.
-197-
120°
3
AS4/938 Tape La up, Unnotched
SDecimen M3-SU1 6
100. Strain Rate
2.5
2
80-
o, 60,
-Id
1.503
40
20
Str
Loke
0 C__4Y
0
!-
0.5
Stroke
·
·
·
·
0.1
0.2
0.3
0.4
Time (sec)
#%A
1N
0.O
12000
-6000
AS4/938 Tape Layup, Unnotched
Specimen M3-SU1 6
10000, Strain Rate: 2 e/min
-5000
CI
8000.
-4000
C
6000
-3000 @-
4000
-2000
"-.
Cn
0d
-J
2000.
S
-a- Longitudinal Strain
'
--0-·
0.1
Figure E.14
-1000,
''Transverse Strain
·
0.2
0.3
Time (sec)
·
0.4
-
S-n
0.5
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M3-SU16.
-198-
120
AS4/938 Tape Layup, Unnotched
Specimen
2.5
100. - Strain Rate
-O
zJe
2
80,
60
-
1.5
/
5
0
40
20
V-
L.
da,
0.5
Stroke
I
12000
1
S
I
0.1
I
i
0I
0.2
0.3
Time (sec)
0.4
12000
-6000
AS4/938 Tape La up, Unnotched
Specimen M3-SU17
C 10000.
Strain Rate: 2 e/min
-5000
-
C
.c
0.5
8000.
-4000
6000.
-3000
C 4000.
-J
o,
-20007
&
2000
I
0.1
Figure E.15
-A-
Longitudinal Strain
---
Transverse Strain
-n
I
0.2
0.3
Time (sec)
-10005,
0.4
0 .5
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M3-SU17.
-199-
120
FI
IF
AS4/938 Tow Placed, Unnotched
Specimen
2.5
1001 - Strain Rat
80.
2 n
60o
1.5
40-
0.5
z
'0
9
-- Stroke
yS
.0.5
p- Load
20ir-
-
30
0
60
90
120
150
180
A
216
Time (sec)
1230A0
I L.V
C
Cd
-6000
AS4/938 Tow Placed, Unnotched
Specimen M2-SU01
10000.
fI.lI
I
-5000
n nnA39 P/min
.trZiniatRat
IIIL.
V·VV'--.
8000.
-4000
6000
-3000 n
4000
-2000
M
C,,
C
0)
cn
0
-J
*- Longitudinal Strain
2000
-1000-o
--0--Transverse Strain
•
0
Figure E.16
I
I
30
60
I
I
I
90 120 150
Time (sec)
I
180
._
210
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M2-SU01.
-200-
120-
3
AS4/938 Tow Placed, Unnotched
Specimen M2-SU02
100. Strc
2.5
/
CO
0.0
8060
-
1 50
.5c
0,
-J
40
- Load
20
2
12000
. 10000
Stroke
I 1
Z
A
u
4
·
·
6
8
Time (sec)
AN
10"
-6000
AS4/938 Tow Placed, Unnotched
pe cimen M2-SU02
-
0.5
-5000
birain mate: u.1 E/min
8000
-4000 R
55 6000
-3000 C,
" 4000
-2000"
C
*
-a-- Longitudinal Strain
3 2000
J
r
I
|I
--i-Transverse Strain
•
|
|
4
6
Time (sec)
Figure E.17
-1000oo
1
•I
.-
110
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M2-SU02.
-201-
3
120-
AS4/938 Tow Placed, Unnotched
Specimen M2-SU03
100. Stra
/
2 0n
80-
9t
-Jd
2.5
1.5Z
60-
v
40
- Load
20
0
L
/1
0
0N
10"
6
4
Time (sec)
12000
-6000
AS4/938 Tow Placed, Unnotched
Specimen M2-SU03
-5000 -I
10000. - Strain Rate: 0.1 e/min
- S~a
C
-'Ii
C
8000.
-4000 0
6000.
-3000
4000.
-20000
-B
0)
C
-0.5
-- 6- Stroke
-a- Longitudinal Strai I
--- Transverse Strain
2000.
•I
I
I
4
6
Time (sec)
Figure E.18
I
-1000o
_-n
-0
1I0
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M2-SU03.
-202-
120-
3
AS4/938 Tow Placed, Unnotched
Specimen M2-SU04
2.5
100. - Strain Rate: 2 e/min
z
80
0-5
-oe
9
0
1.5Z
60-
1
2
40Load
20
0.5
A
-- Stroke
I.'
u
SI
•i
0.1
I
n
I
0.4
0.3
0.2
Time (sec)
1 0n0nII(33
AS4/938 Tow Placed, Unnotched
Specimen M2-SU04
C/E
-6000
-5000 -i
10000- - Strain Rate: 2 e/min
-c
o.5
8000.
-4000
6000.
-3000
4000.
-20001
3
2000.
--
·
Figure E.19
-1000o
Transverse Strain
--i-
0.1
Longitudinal Strain
·
0.2
0.3
Time (sec)
·
0.4
-n
0 .5
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M2-SU04.
-203-
0
120
3
AS4/938 Tow Placed, Unnotched
Specimen- M2-SU05Strai
100, -Strain Rate: 0.0042 s/min
2.5
2
80
z
60
-Id
%%O
1.5
40'
1'
-4- Load
20'
0.5
-h• Stroke
n
•I
l
)i
30
0C
12000
. 10000
C
Il
60
II
Il
l
120
150
180
I
90
Time
(sec)
A
I
10
2
-6000
AS4/938 Tow Placed, Unnotched
R5~npimen M2-.S! Inr
- -5000
Strain Rate: 0.0042 e/min
-
8000
-4000
&5 6000
-3000#
*
S-2000 *
4000
C
9 2000
-"-- Longitudinal Strain
-
1-1000
----Transverse Strain
0
*
1
a
a
0
Figure E.20
I -n
1
v
30
60
90 120 150
Time (sec)
180
210
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M2-SU05.
-204-
120-
3
AS4/938 Tow Placed, Unnotched
S•
InA
-KaOI
1cimAn
p
III
2.5
100, Strain Ra
-
2
80
0
"g
o
1.50
Ca60
10
40
-4 -- Load
s-- Stroke
20
0
0
n
I
ir
0
30
60
I
I
|•
I
IIn
I
120 150 180
90
0.5
216
Time (sec)
12000
-6000
AS4/938 Tow Placed, Unnotched
Specimen M2-SU06
10000 - Strain Rate: 0.0042 s/min
-5000 -I
C
LM
%*ag 8000
CD
-4000 R
6000
-3000 00
4000.
-20007-a
9-.
o,
Cr
0~J
ain
2000.
-0- Transve rse Strain
--
0
Figure E.21
-
I
30
60
I
I
I
90 120 150
Time (sec)
I
180
-
-1000 20
I-A
210
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M2-SU06.
-205-
120
AA02&ý
Placed, Unnotched
AS4/938
*IL Tow
&A
Specim
2.5
100, - Strain F
C
02
80
Cu
60
-
0o
-Je
cc
9
1.5
/
0.5
40
!
20
Stai
0
Stroke
I
I
--
60
30
0
--
~
___
I___
____
~
___-
-- I-
__
90 120 150 180
Time (sec)
nn
1200
C
6-5000
Rat
-Strain
8000.
C
-4000 9
6000.
-3000 -
"
-
4.I
C
0I
-J
40002
2000.
0
216
-6000
AS4/938 Tow Placed, Unnotched
Specimen M2-SU07
10000.
0.5
-2000w
-
Longitu dinal Strain
---
-1000,'
-0- Transverse Strain
I
I
30
60
-
0
Figure E.22
I
I
I
-t
I
90
120 150
Time (sec)
180
210
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M2-SU07.
-206-
120-
3
AS4/938 Tow Placed, Unnotched
Specimen M2-SU08
2.5
100. Str4
-J
80-
2
60-
1.5
-,
20
u
1
1
40'
6'
to
Load
7--F--
6
i
/'t
I
Stroke
n
I
4
6
Time (sec)
2
0
0.5
8
10
10')l
S10000
-6000
AS4/938 Tow Placed, Unnotched
Specimen M2-SU08
,-!--
-5000
0.1
Rate:
iartS
n
8000
-4000
C5 6000
4000
.
-3000 1*
,,
-v
-2000
- Longitudinal Strain
, 2000O
-1000oo
--f-- Transverse Strain
4
4
6
Time (sec)
Figure E.23
0
.-n
10
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M2-SU08.
-207-
120-
3
AS4/938 Tow Placed, Unnotched
Specimen M2-SU09
100- Strain Rate: 0.1 e/min
.Y
/
-
2.5
80o 60
1.5
CU
0E
12
-J
40,&
I
20,
I
ad
0.5
-- r- Stroke
I
n
v
I
·I
I
8
4
6
Time (sec)
2
19nnn
C
-
Q~r~an D~+ 1
LIQI IaIL:
L."
C
-6000
AS4/938 Tow Placed, Unnotched
Specimen M2-SU09
10000.
7@
·
A I
.
10
10
-5000
lmir
111
CI#
8000-
-4000 D
CD
6000.
-3000
3o>4000.
-2000
3-
2000.
--
-
Longitudinal Strain
-1000o
-- l- Transverse Strain
I
i
I
'
4
6
Time (sec)
Figure E.24
I
-.
n
10
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M2-SU09.
-208-
120o
Unnotched
AS4/938 Tow Placed,
^ 16
0
Specime
A%
2.5
100. Strain R;
-
80O
-
1.52
60-
40'
-
/
oad
20
0.5
n- Stroke
0
0
12000
C
~A<~II
--
I
0.1
I
i
i
0.4
0.3
0.2
Time (sec)
I
0oi'
-6000
AS4/938 Tow Placed, Unnotched
Specimen M2-SU10
10000. - Strain Rate: 2 E/min
-5000
-I
8000.
-4000
6000.
-3000 %
4000.
-20009
C.
C
-J
----
2000.
Longitudinal Strain
-1000 -
--a,- Transverse Strain
I._n
0.1
Figure E.25
0.2
0.3
Time (sec)
0.4
0.5
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M2-SU10.
-209-
120
A
100
2.5
-Jd
80
2
60
1.5
40
1
20
0.5
0
0
0.1
0.2
0.3
Time (sec)
0.4
1 0nnn
I
L.
3
3
n
0.5
-OUUU
AS4/938 Tow Placed, Unnotched
Specimen M2-SU11
10000. - Strain Rate: 2 e/min
-5000
CO
C
8000-
-4000
6000.
-3000
4000.
-2000•
'
C
Cn
0
IC
-- *- Longitudinal Strain
2000.
-1000-~
--0- Transverse Str ain
0.1
Figure E.26
0.2
0.3
Time (sec)
·
.-n
0.4
C).5
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M2-SU11.
-210-
120-
AS4/938 Tow Placed, Unnotched
ISr•
pl
imen IlSI
I10
I I II
2.5
100' -Strain Ra
80-on
9
2
-
1.5 ,
3
3
10
6040-
-
/
0.5
'ad
20
a- Stroke
0
v
12000
C
I
0.1
I
1
0.2
0.3
Time (sec)
0.4
n
o.'
-6000
AS4/938 Tow Placed, Unnotched
Specimen M2-SU12
10000 - Strain Rate: 2 E/min
-5000-
8000
-4000 c
C
6000
-3000
Cd
4000
-2000Y
CI
-B
0
-J
-1000
A--- Longitudinal Strain
2000
-•E- Transverse Strain
I
0.1
Figure E.27
I
II
·
·
0.2
0.3
Time (sec)
·
0.4
-n
0.5
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M2-SU12.
-211-
-
120
2.5
100
80
2
0
z
Jed
60
1.5 ,
0
40
1 '
20
0.5
0
2
0
4
6
Time (sec)
8
n
10
Pl 1
12000
. ooo10000
C
-OUVU
AS4/938 Tow Placed, Unnotched
Specimen M2-SU13
-
-5000
Strain Rate: 0.1 e/min
- Sta
8000
&5 6000
*
4000
3
2000
-4000 5
-3000
-
*
-2000w
---- Longitudi nal Strain
---
-1000.'
Transvenr e Strain
I
-n
1I0
-
4
6
Time (sec)
Figure E.28
CD
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M2-SU13.
-212-
120 I
3
~pecirr
AS4/938 Tow Placed, Unnotched
iI*
A^r
Speci m
1~ 1.4
A
2.5
100. - Strain F
2
80O
c
-I0o
wfww
Cu
60-
-
1.5w
/
40,
20U
J
K
-- -
i
0
30
12000
C
0.5
SStroke
-F
--Stroke
I
I
I
I
I
I
I
I
I
120
150
180
60
90
Time (sec)
n
21(
-6000
AS4/938 Tow Placed, Unnotched
Specimen M2-SU14
-5000
10000. - Strain Rate: 0.0042 s/min
a..
4'
C
C
.3
C
0n
-J
8000
-4000 (
6000
-30000
4000,
-20000"
--- Longitudinal Stra in
---0- Transverse Strai n
2000,
-10002•
-n
0
Figure E.29
30
60
90 120 150
Time (sec)
180
210
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M2-SU14.
-213-
120
2.5
100
2
80
doot
1.5
Ca 60
-9
40
20
0.5
0
0.1
0
12000
S10000
C-
0.2
0.3
0.4
Time (sec)
0.
-6000
AS4/938 Tow Placed, Unnotched
Specimen M2-SU15
-5000
- Rttin Rnte: 9 P/min
liil
·
•·
•UV
•
• •
ibm
-4000 !
8000
&56000
-3000 .
Ad
.• 4000
-2000
C
o9 2000
I
---
Longitudinal Strain
-I--
Transverse Strain
-10002
I
0.1
Figure E.30
0.2
0.3
Time (sec)
0.4
-n
0.5
-
Plots of Load, Stroke, Longitudinal Strain and Transverse
Strain versus Time for Specimen M2-SU15.
-214-
80
AS4/938 Tape Layup, 19 mm Slit
Specimen M3-SN01
Strain Rate: 0.0042 e/min
1.5
60-
0D
-J
CD
40
1
20
0.5
O
3
0
---- Load
-. _- Stroke
U
i
I
|
20
I
I
60
40
Time (sec)
80
10000
AS4/938 Tape Layup 19 mm Slit
Specimen M3-SNO1
8000. Tested at: 0.0042 E/rnin
CO
=a6000.
C
(-,
I
4000.
2000
111111k_ý
-&-- Far-Field Strair1
-0-
0.
Figure E.31
I
20
I
Notch-Tip Straiin
II
60
40
Time (sec)
80
100
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M3-SNO1.
-215-
80
AS4/938 Tape Layup, 19 mm Slit
Specimen M3-SNO2
Strain Rate: 0.0042 elmin
-1.5
60z
0
-J
CD
40
-
20-
0
0.5
-
-
B·
0--
I
-4-
Load
---
Stroke
/A
I
0v
20
40
60
Time (sec)
80
106
0
20
60
40
Time (sec)
80
100
.41
000n
I 800
800
600
c
400
0-0
C)
200
Figure E.32
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M3-SN02.
-21&
80
2
AS4/938 Tape Layup, 19 mm Slit
Specimen M3-SN03
Strain Rate: 0.0042 e/min
1.5
60
CD
-
o
03
40
i,0
20
d
0.5
ke
II
r
a
a
A
20
40
60
Time (sec)
80
100
20
40
60
Time (sec)
80
100
r
C
L.
C"
I-
0
Figure E.33
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M3-SNO3.
-217-
80 I
O
AS4/938 Tape Layup, 19 mm Slit
Specimen M3-SN04
Strain Rate: 0.0042 E/min
60
1.5
40
1
20
CD
03
0.5
--- Load
8
I
·
·I
L
20
40
60
Time (sec)
80
106
20
40
80
100
C
C-
=a
0
Figure E.34
60
Time (sec)
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M3-SN04.
-218-
80
AS4/938 Tape Layup, 19 mm Slit
Specimen M3-SN05
Strain Rate: 0.0042 E/min
1.5
60
(n
-o
40
0
z0
9
20
-- Load
-0.5
Stroke
n
I
I
220
60
40
Time (sec)
80
11
20
40
60
Time (sec)
80
100
10000.
8000.
C
I- 6000
403
C/
1..
C'
4000
2000
0
0
Figure E.35
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M3-SN05.
-219-
80
AS4/938 Tape Layup, 19 mm Slit
Specimen M3-SN06
Strain Rate: 0.1 dJmin
1.5
60
z
S40
1
D
oJ
20
0.5
-
.=J
.'0ý-
n r
I
I
0v
-- +-- Load
Stroke
-.--
2
.0
|
*
*
3
5
Time (sec)
10000n
AS4/938 Tape Layup, 19 mm Slit
Specimen M3-SN06
Tested
at: 0.1 e/min
8000.
-
=a6000,
CO
I.-
4000.
2000
-- Far-Field Strain
-- Notch-Tip Strain
A
,
I
0
Figure E.36
|
I_|
|
2
3
I•
Time (sec)
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M3-SNO6.
-220-
80
AS4/938 Tape Layup, 19 mm Slit
Specimen M3-SNO7
Strain Rate: 0.1 E/min
60'
x
-
z
-Jz
9c
1.5
-e
1
40
20
*- Load
I
)
1
2
3
Time (sec)
0.5
Stroke
,I
C
I
4
A
5
1
#
C
(C
"=a
CO
Time (sec)
Figure E.37
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M3-SN07.
-221-
,,
60
AS4/938 Tape Layup, 19 mm Slit
Specimen M3-SN08
Strain Rate: 0.1 E/min
60
1.5
40
1
CD
o
20
0.5
0ad
ova
3-- Stroke
-
01
1
2
3
Time (sec)
4
1
2
3
Time (sec)
4
n
5
I fnnf
I
C
C
Cn
L-
(I)
0
Figure E.38
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M3-SNO8.
-222-
1~
h
BU
AS4/938 Tape Layup, 19 mm Slit
Specimen M3-SN09
Strain Rate: 0.1 e/min
1.5
60O
1CD
3
-c 40
0.5
20
-+-- Load
---- Stroke
.n
n
0
1
3
2
Time (sec)
4
5
0
1
2
3
Time (sec)
4
5
C
L.
W3
Figure E.39
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M3-SNO9.
-223-
80
AS4/938 Tape La up, 19 mm Slit
Specimen M3-SN10
Strain Rate: 2 e/min
1.5
60
7
CU
0
-Z
z
.Y40
3
0.5
20 I/I
__rna'
. 0.1
T--
1
I
·
·
Time (sec)
·
0.2
---
Load
--
Stroke
I
n
o.0
ot
..
C
e-
=a
Time (sec)
Figure E.40
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M3-SN10.
-224-
80
AS4/938 Tape Layup, 19 mm Slit
Specimen M3-SN11
Strain Rate: 2 elmin
1.5
60o
Cn
00
40
70
i
-l
20
0
-- Load
f
Vx-.Oý.
0V
-
0.5
Stroke
N
0.1
Time (sec)
0.2
4 Anf%
I VVV
800
C
.a
C
600
400
200
Time (sec)
Figure E.41
3
Plots.of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M3-SN11.
-225-
80
V.,
AS4/938 Tape Layup, 19 mm Slit
Specimen M3-SN12
Strain Rate: 2 /min
60
1.5
o
V1
7X,
40
-o
0
0.5
-j
20-
J
"-ý_I
f
----
Load
----
Stroke
·n
0.1
0.2
0.
0.2
0.3
Time (sec)
1
C
C-
C
C,)
0
Figure E.42
0.1
Time (sec)
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M3-SN12.
-226-
80
2
AS4/938 Tape Layup, 19 mm Slit
Specimen M3-SN14
Strain Rate: 2 e/min
1.5
60
0o
z
o, 40 I0C
1
7
9
-J
CD
3
3
20 I-
----
z
Load
0.5
-Li Stroke
.n
0.1
Time (sec)
0.2
o.3
0.2
0.3
4IflflA
I
C
C
CO
0
Figure E.43
0.1
Time (sec)
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M3-SN14.
-227-
80
I
2
AS4/938 Tape Layup, 19 mm Slit
Specimen M3-S 15
Strain Rate: 2 e/min
60
1.5
40
1
20
CD
.0.5
y
-+-- Load
--i-!
0.1
Time (sec)
Stroke
i
0.2
C
tC,h..
0
Figure E.44
0.1
Time (sec)
0.2
0.3
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M3-SN15.
-228-
80
AS4/938 Tape Layup, 19 mm Slit
Specimen M3-SN16
Strain Rate: 0.1 e/min
1.5
60
z
40
0
0.5
20
d
- Stroke
_'e
I
12
I
I
_
-
3
4
2
3
Time (sec)
4
Time (sec)
0
5
Cd
C
I-
0
Figure E.45
1
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M3-SN16.
-229-
80AS4/938 Tow Placed, 19 mm Slit
2
60
1.5
Specimen M2-SNO1
Strain Rate: 0.0042 E/min
0.
z
40
ia
9
10
-J
K-
20
Al0
I
-Load
-6I
I
I
0.5
Stroke
I
n
20
40
60
80 100
Time (sec)
120
146
20
40
60
80
Time (sec)
100
120
140
C4
"..
0
Figure E.46
Plots. of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M2-SNO1.
-230-
__
80
1.5
60
1
v40
D
0.5
20
n
0
0.1
0
0.1
Time (sec)
0.2
C
1,
C,
1C.
Figure E.47
Time (sec)
0.2
0.3
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M2-SN02.
-231-
80
AS4/938 Tow Placed, 19 mm Slit
Specimen M2-SNO3
Strain Rate: 0.1 E/min
1.5
60
- 40
o
J
0.5
20
-+- Load
--z•.-- Strok e
0
0
·
·
·
3
Time (sec)
1
~C
C
C,)
Time (sec)
Figure E.48
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M2-SN03.
-232-
80
60
2
AS4/938 Tow Placed, 19 mm Slit
Specimen M2-SN04
rt
a
n
ate:
s
1.5
m
-
z
_ýd
40
1
-
%l
09
9J
20
U0.b
*- Load
6-
I'.
U
I•
I
0.1
I
Time (sec)
I
0.2
Stroke
I
A
0.O
1
C
C
1r
Time (sec)
Figure E.49
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M2-SN04.
-233-
8aA
AS4/938 Tow Placed, 19 mm Slit
Specimen M2-SN05
Strain Rate: 0.O0
1.5
60
-g 40
-J
0
7
20
lp"
100001
|
-*-
Load
-z
Stroke
0.5
A1
|
:
20
100 120
a
40
I
60 80
Time (sec)
I
1
46
AS4/938 Tow Placed, 19 mm Slit
8000. Tested at: 0.0042 e/min
C
C
L.
cl,
-
600040002000
0
-(] 20
C0
Figure E.50
S
40
-
--
Far-Field Str ain
-•--
Notch-Tip Str rain
I
i
60 80
Time (sec)
I
I
100
120
140
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M2-SNO5.
-234-
II
A
UU AS4/938 Tow Placed. 19 mm
Slit
Specime
Strain R;
60-
1.5
" 40-
·1
0
20-
----Load
*0.5
-n-- Stroke
I
I
I
0
1
2
3
4
Time (sec)
5
6
0
1
2
3
4
Time (sec)
5
6
0
I MInM
800
C
S600
c- 400
200
Figure E.51
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M2-SN06.
-235-
__
__"
tsU '
AS4/938 Tow Placed, 19 mm Slit
Specimen M2-SN07
Strain Rate: 0.1 e/min
,
1.5
60-
40-
3
0.5
z
20-
---- Load
- Stroke
_x-6'•
f%
U•
0
i
I
I
1
2
1
2
n
!
4
5
6
4
3
Time (sec)
5
6
3
Time (sec)
1^N•
I
C
h..
0
Figure E.52
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M2-SN07.
-236-
80
2
AS4/938 Tow Placed, 19 mm Slit
Specimen M2-SN08
Strain Rate: 0.0042 F/min
1.5
60CU
0-ft
-J
01C
o 40
20
/r
+- Load
0.5
6-- Stroke
U
I
I
20
40
In
60
80 100
Time (sec)
120
146
.4
AAA
I
C
Cn
Time (sec)
Figure E.53
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M2-SNO8.
-237-
2
AA
-
AS4/938 Tow Placed, 19 mm Slit
Specimen M2-SNO9
Strain Rate: 2 d/min
1.5
60,
S40
0.5
1
20
0.5
OAr
-- Stroke
I|
)C
0
I
I
0.1
I
Time (sec)
I
0.2
C
C
em
Ci:
L.
0
Figure E.54
0.1
Time (sec)
0.2
0.3
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M2-SNO9.
-238-
80
2
AS4/938 Tow Placed, 19 mm Slit
Specimen M2-SN10
Strain Rate: 0.1 e/min
1.5
60
2j
Z
40
3
0.5
20
- Load
4
A
Ad
-- Stroke
n
'
=
t
0
1
2
3
4
Time (sec)
5
0
1
2
3
4
Time (sec)
5
6
C
C
(-
Figure E.55
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M2-SN10.
-239-
,,
r
AS4/938 Tow Placed, 19 mm Slit
Specimen M2-SN11
Strain Rate: 0.0042 E/min
-
60
4
1.5
0
z
o 40
1 CD
9
20
0.5
*- Load
-s- Stroke
0)
_
I
20
0C
40
iA
I 8000VV
A
d
1
-.. . I'•
·
·I
I
·
I
80 100
60
Time (sec)
aJ
·
I
120
-
N
146
f%1JA
'• .'
d
AS-4/93;• I OW Placeo, 19 mm ilit
Specimen M2-SN1 1
8000 Tested at: 0.0042 e/min
C
6000
aC
t4000
=a
2000
-
Far-Fi eld Strain
- Notch -Tip Strain
0w'
Figure E.56
.
0
ffl
|
20
~I
40
II|
60 80
Time (sec)
100 120
140
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M2-SN11.
-240-
80
AS4/938 Tow Placed, 19 mm Slit
Specimen M2-SN12
QtrZ;rn
Dnnen
VII CIIII
I~QI~.
02 c-/m;n
1.5
60-
C,
0
C
I
3
20-
0.5
Stroke
A0)
VC
L
___
____
I
0.1
Time (sec)
I
0.2
I
I0
0o.3
1
C
r-
L_
C3
Time (sec)
Figure E.57
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M2-SN12.
-241-
80
AS4/938 Tow Placed, 19 mm Slit
Specimen M2-SN13
Strain Rate: 0.1 E/min
1.5
60-
(D
z
40
7
33
-0O
3
0.5
20-
n
)
0C
I
I
I
-
-
-
1
2
3
4
Time (sec)
---
Load
--
Stroke
-
5
0
6
-
C
C
L..
Time (sec)
Figure E.58
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M2-SN13.
-242-
80
AS4/938 Tow Placed, 19 mm Slit
Specimen M2-SN14
Strain Rat(
1.5
60
V
40-
CD
-
-
3
0
-j
20-
~0.5
--
Load
6r- Stroke
vC))
4 AAAA
I
X
n
I
I
I
I
20
40
60
80 100
Time (sec)
II
120
A
146
r
AS4/938 Tow Placed, 19 mm Slit
Specimen M2-SN14
8000. Tested at: 0.0042 e/min
1
t-
6000.
4000.2000.
n.
v
---- Far-Field Strain
---- Notch-Tip Strain
L•II
Y
I
0
Figure E.59
20
I
•
40
I
1
I
I
II
I
II
II
60 80
Time (sec)
100
120
140
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M2-SN14.
-243-
=AA
AS4/938 Tow Placed, 19 mm Slit
Specimen M2-SN15
Strain Rate: 2 E/min
1.5
60o
- 40
0.53
20
0.5
*--Load
z
-- Stroke
I·
A _
I·
0.1
'I
I·
Time (sec)
I·
n
0.2
o.f
0.2
0.3
1
Ch-
0
Figure E.60
0.1
Time (sec)
Plots of Load, Stroke, Far-Field Strain and Notch-Tip Strain
versus Time for Specimen M2-SN15.
-244-
160
AS4/938 Tape Layup, 51 mm Slit
140 -Specimen M3-LN01
Strain Rate: 2 O/min
120
z~100
S80
2
-
S60o
40
-
1
-
20
./
r
-
V0
_.
ýI
--
----
Load
---
Stroke
O.3
-
0.1
Time (sec)
0.2
0
12000
10000
'28000
,96000
C
C5 4000
2000
0
3
Time (sec)
Figure E.61
Plots of Load, Stroke, Far-Field Strain and Strains from
Notch-Tip versus Time for Specimen M3-LN01.
-245-
160 I1
AS4/938 Tape Layup, 51 mm Slit
140 Specimen M3-LN03
Strain Rate: 0.1 E/min
120,
-
3
Z100.
2
80
S60
1
40-
----
.=
I'l
·
0.5
I
C
UVV
1
·
2
1.5
Time (sec)
9
·
2.5
0
0
0AA
I
AS4/938 Tape Layup, 51 mm Slit
Specimen M3-LN03
0000--Tested at: 0.1 e/min
C
8000-
V.
0
6000-
IL
Load
-
20
I
C
4000-
Cu
LL
2000.
01
C0
j)
Figure E.62
m
0.5
|
|
1.5
2
Time (sec)
2.5
Plots of Load, Stroke and Far-Field Strain versus Time for
Specimen M3-LN03.
-246-
160 AS4/938 Tape Layup, 51 mm Slit
M3-LN04
140 -Specimen
Strain Rate: 0.0042 Emin
3
120
CD
8100
r/
S80
2
0d
JL
OU F
1
40
d
20
0
ke
A
20
40
Time (sec)
60
80o
12000
10000
Z8000
16000
C
& 4000
2000
0
Time (sec)
Figure E.63
Plots of Load, Stroke, Far-Field Strain and Strains from
Notch-Tip versus Time for Specimen M3-LN04.
-247-
160 AS4/938 Tape Layup, 51 mm Slit
M3-LN05
140 -Specimen
Strain Rate: 0.0042 e/min
3
120
00oo
-9
2
o 80
60
1
40
-4-
20
U
Load
I
i1
20
40
Time (sec)
60
I
E0
12000
10000
Z8000
16000
C
cn 4000
2000
0
0
Time (sec)
Figure E.64
Plots of Load, Stroke, Far-Field Strain and Strains from
Notch-Tip versus Time for Specimen M3-LN05.
-248-
160-
AS4/938 Tape Layup, 51 mm Slit
140 - Specimen M3-LN06
Strain Rate: 0.1 E/min
120,
3
-9
z o00
0
2 20
S80
0
1
40
3
s- Load
20
U
iI
--- Stroke
-
I
I
I
0
0.5
1.5
2
1
Time (sec)
2.5
0
0.5
1
2
1.5
Time (sec)
2.5
0n
3
4'Ann
I
.1
CD
0-.
UL.
!
=m
L_
L.
Figure E.65
Plots of Load, Stroke and Far-Field Strain versus Time for
Specimen M3-LN06.
-249-
160 AS4/938 Tape Layup, 51 mm Slit
140 Specimen M3-LN07
Strain Rate: 2 s/min
120,
0
-7
2
- 80o
0
,
i3
6040
-
20
---
r/
I
0.1
I
Time (sec)
I
Load
Stroke
I
0.2
4 nInnn
I LVVU~
C1
AS4/938 Tape Layup, 51 mm Slit
Specimen M3-LN07
0000. Tested at: 2 e/min
8000.
6000
LL
L
4000,
2000.
II
U.
0
Figure E.66
-
a
a-
I
0.1
0.2
Time (sec)
0.3
Plots of Load, Stroke and Far-Field Strain versus Time for
Specimen M3-LN07.
-250-
160
4
AS4/938 Tape Layup, 51 mm Slit
Specimen M3-LN08
Strain Rate: 0.1 e/min
140
.3
120
z^1 00
-2
-O6o
80
",.I.1
40
-- *- Load
20o
#'t
-a-- Stroke
A
e
....
0
0
0.5
1
1.5
2
Time (sec)
2.5
3.O
0.5
1
1.5
2
Time (sec)
2.5
3
12000
10000
8000
C
% 6000
6-o
LL
LL
LL
2nn
2f000
lVVV
0
0
Figure E.67
Plots of Load, Stroke and Far-Field Strain versus Time for
Specimen M3-LN08.
-251-
d
__
r'•
F
AS4/938 Tape Layup, 51 mm Slit
M3-LN09
140. -Specimen
Strain Rate: 0.0042 elmin
3
120
2
-00
cD
o 60
1
40
id
20
)ke
n
20
u0
40
Time (sec)
60
80
12000nn
AS4/938 Tape Layup, 51 mm Slit
Specimen M3-LN09
,-.10000. -Tested at: 0.0042 E/min
8000
. 6000.
. 4000-
UL.-I
U
-
2000.
0
0
Figure E.68
I
20
1
I
40
Time (sec)
60
80
Plots of Load, Stroke and Far-Field Strain versus Time for
Specimen M3-LN09.
-252-
160 AS4/938 Tape Layup, 51 mm Slit
M3-LN10
140 Specimen
Strain Rate: 2E/min
120
CO
0'
7 80
3
3
0
S60
40
20
U
__ ~
I
I
·
S
0.1
·
Time (sec)
·
---
Load
---
Stroke
I
0.2
12000
10000
'28000
16000
cn 4000
2000
0
Time (sec)
Figure E.69
3
Plots of Load, Stroke, Far-Field Strain and Strains from
Notch-Tip versus Time for Specimen M3-LN10.
-253-
160 AS4/938 Tape Layup, 51 mm Slit
M3-LN11
140 -Specimen
Strain Rate: 2 E/min
3
120
-
-
-n
Soo00
21
- 80
,60
1
40
-
20
-- Load
Stroke
/5
I
0.1
I
I
0
0.2
0.3
0.2
0.3
Time (sec)
1
C
C
(,,
-O
Y
"0)
CO
LL
I!.
LL
Ia
0
Figure E.70
0.1
Time (sec)
A
Plots of Load, Stroke and Far-Field Strain versus Time for
Specimen M3-LN11.
-254-
4
160-
AS4/938 Tape Layup, 51 mm Slit
140. Specimen M3-LN12
Strain Rate: 0.1 E/min
120,
3
-5
2
S80'
60
1
40-
-#-
20-
r-
0(
7
I
0.5
1
I
I
1.5
2
Time (sec)
Load
Stroke
I
2.5
1
3
IUUUv
10000
'•8000
16000
C
5 4000
2000
0
Time (sec)
Figure E.71
Plots of Load, Stroke, Far-Field Strain and Strains from
Notch-Tip versus Time for Specimen M3-LN12.
-255-
IAA
lbUI
AS4/938 Tape Layup, 51 mm Slit
140 Specimen M3-LN13
Strain Rate: 0.0042 e/min
120
.3
2
S80'
0
60o
1
40-
- Load
20'
- Stroke
I
An
0V
2
20
40
Time (sec)
60
In
80
ff 0
I0:UUU
-
AS4/938 Tape Layup, 51 mm Slit
Specimen M3-LN13
0000 -Tested at: 0.0042 s/min
-
8000
6000
Li
4000.
I .
Ca
U._
(,-
2000. Nii
0
n
Figure E.72
20
40
Time (sec)
60
80
Plots of Load, Stroke and Far-Field Strain versus Time for
Specimen M3-LN13.
-256-
160
AS4/938 Tape Layup, 51 mm Slit
M3-LN14
-Specimen
140
Strain Rate: 2 e/min
120
3
CO
z100
20
S80
3
7
9 ,,
OU
3
1
40
20
..S
Load
-
-
-
- Stroke
A
A
0.1
0
0.2
0.3
Time (sec)
1200C
#.
IIr
AS4/938 Tape Layup, 51 mm Slit
Specimen M3-LN14
0000,
Tested at: 2 E/min
1,
C
8000
6000
U_
-.
L.
4000
2000
0
-
0I
Figure E.73
,
0.1
Time (sec)
0.2
0.3
Plots of Load, Stroke and Far-Field Strain versus Time for
Specimen M3-LN14.
-257-
•
AA
16U
AS4/938 Tape Layup, 51 mm Slit
140- Specimen M3-LN15 e/min
Strain Rate: 0.0042
120
3
z.100
SO
2
1
80
r/
60
1
40
20
----
Load
-6-
Stroke
I
0o
IVV
UU
20
40
Time (sec)
60
n
80o
,
AS4/938 Tape Layup, 51 mm Slit
Specimen M3-LN15
0000
1
-Tested at: 0.0042 e/min
8000
6000
ecc
La
L 4000
".
ui
2000
,
AI
I
V
C-0
Figure E.74
20
40
Time (sec)
60
80
Plots of Load, Stroke and Far-Field Strain versus Time for
Specimen M3-LN15.
-258-
· __
1_1
AS4/938 Tape Layup, 51 mm Slit
M3-LN16
140 .Specimen
Strain Rate: 0.1 E/min
120,
3
z100
'2
- 80
ctj 60
Af
1
40
Load
20
Stroke
I
U0
3
3
0.5
1
1.5
2
2.5
n
3"
Time (sec)
1 0UUU
10000
Z8000
16000
r.
&54000
2000
0
Time (sec)
Figure E.75
Plots of Load, Stroke, Far-Field Strain and Strains from
Notch-Tip versus Time for Specimen M3-LN16.
-259-
160
AS4/938 Tow Placed, 51 mm Slit
140 -Specimen M2-LN01
Strain Rate: 0.0042 e/min
120,
3
Y2100
a
20e
S80
3
60
3
40-
----Load
20,
-6-
20
40
I
60
80 100
Time (sec)
Stroke
I
n
120
146
120
140
51 mm Slit
FJmin
M2-LN01
Placed,
Tow
AS4/938
Placed, 51 mm Slit
Specimen
0.0042
at:Tow
-Tested
Specimen M2-LNO1
,10000- -Tested at: 0.0042 elmin
C
12000
8000.
8
6000.
. 4000
L
i
1
I
0.C
C
Figure E.76
20
40
60
80
Time (sec)
100
Plots of Load, Stroke and Far-Field Strain versus Time for
Specimen M2-LNO1.
-260-
160 AS4/938 Tow Placed, 51 mm Slit
140. .Specimen M2-LN02
Strain Rate: 2 E/min
120,
-
00
0n
.
CD
io
-o 80
-J
a
60
40
- Load
20
- Stroke
0.1
0.2
Time (sec)
12000
10000
S8ooo
16000
5 4000
2000
0%
V0
Figure E.77
0.1
Time (sec)
0.2
0.3
Plots of Load, Stroke, Far-Field Strain and Strains from
Notch-Tip versus Time for Specimen M2-LN02.
-261-
160 AS4/938 Tow Placed, 51 mm Slit
M2-LN03
140 .Specimen
Strain Rate: 0.0042 e/min
120
3
/
z100
c 80
0 60
1
*1
40
20
-+- Load
r
-&
I
20
40
60
80 100
Time (sec)
Stroke
1
120
0
140
12000
10000
.Z8000
16000
,5
4000
2000
0
Time (sec)
Figure E.78
Plots of Load, Stroke, Far-Field Strain and Strains from
Notch-Tip versus Time for Specimen M2-LN03.
-262-
4
160
AS4/938 Tow Placed, 51 mm Slit
M2-LN04
140 -Specimen
Strain Rate: 0.1 e/min
120
3
1o00
S80
2
S60
1
40
ad
20
0
roke
1
2
3
Time (sec)
4
0
5
12000
10000
Z8000
,96000
CD 4000
2000
04
Time (sec)
Figure E.79
Plots of Load, Stroke, Far-Field Strain and Strains from
Notch-Tip versus Time for Specimen M2-LN04.
-263-
•11 Jllb.ill
-
AS4/938 Tow Placed, 51 mm Slit
M2-LN05
140 -Specimen
Strain Rate: 0.0042 e/min A
120
3
z 100
2
o, 80
60
4020,
3
3
-4- Load
I
-
/I
L
uc)
I
I
Stroke
I
!
II
20
40
60
80 100
Time (sec)
120
An
146
1ZUUU
10000
Z8000
4000
6
O'4000
2000
0
Time (sec)
Figure E.80
Plots of Load, Stroke, Far-Field Strain and Strains from
Notch-Tip versus Time for Specimen M2-LN05.
-264-
160 AS4/938 Tow Placed, 51 mm Slit
M2-LN06
1402 Specimen
Strain Rate: 2 e/min
?
3
120
1zi 00
20
2 c1
S80
60
40
Load
20
Stroke
0.2
O.3
0.2
0.3
0
I.,
U0
0
0.1
0
0.1
Time (sec)
C
C
r,=
1...
0-.
=1
I.
LL
Ci
Figure E.81
Time (sec)
Plots of Load, Stroke and Far-Field Strain versus Time for
Specimen M2-LN06.
-265-
160
AS4/938 Tow Placed, 51 mmSlit
z
140 -Specimen M2-LN07
St
I/
120
z100
3
-9
J
80
2
.j 40
40
-4-- Load
-,n-- Stroke
20
00
IIo
I
20
40
20
40
I
60
I
I
I
80 100 120
Time (sec)
1
n
146
12000
10000
Cd
4-.
8000
-o
6000
CU
U-
4000
2000
0
0
Figure E.82
60 80 100
Time (sec)
120
140
Plots of Load, Stroke and Far-Field Strain versus Time for
Specimen M2-LN07.
-266-
· __
.,=
_ ='
r
AS4/938 Tow Placed, 51 mm Slit
140- -Specimen
Strain RatE
3
120'
Cn
Z100
80'
2.
60
40
20
I'
U0
0
-•-- Load
•- - Stroke
I
1
I
2
3
Time (sec)
I
4
5
10000
Z 8000
16000
C
&54000
2000
0
Time (sec)
Figure E.83
Plots of Load, Stroke, Far-Field Strain and Strains from
Notch-Tip versus Time for Specimen M2-LNO8.
-267-
.Ji AA
AS4/938 Tow Placed, 51 mm Slit
140 St
Si
.3
120
z100-
2
S80
60
c!
13
40-
d
20,
ke
n
I
u0
1
2
3
Time (sec)
4
5
12000.
AS4/938 Tow Placed, 51 mm Slit
Specimen M2-LN09
10000. -Tested at: 0.1 E/min
.8000
" 6000.
0-o
a 4000,
EL.-
u- 2000
u`
2
3
Time (sec)
Figure E.84
Plots of Load, Stroke and Far-Field Strain versus Time for
Specimen M2-LN09.
-268-
I tbU AS4/938 Tow Placed, 51 mm Slit
.JI AII•A
-
140 -Specimen M2-LN10
Strain Rate: 0.0042 e/min
120
'100"
.3
I-
zoo
So80
2
C.
60
1
4020,
A
-- Load
/, , r I I I
f 20 40 60
I
I
V0
II
80
Time (sec)
)
C
n- Stroke
I
100
I
I
I
!
I
120
145
120
140
12000
AS4/938 Tow Placed, 51 mm Slit
Specimen M2-LN10
0000. -Tested at: 0.0042 e/min
1.
800060004000.
I.
K
_
-
Cu
,L 2000.
0
0)
Figure E.85
20
40
60
80
Time (sec)
100
Plots of Load, Stroke and Far-Field Strain versus Time for
Specimen M2-LN1O.
-269-
160° AS4/938 Tow Placed, 51 mm Slit
4
120 I-
3
M2-LN11
140 -SDecimen
S
z 00
2T
80
3
0
40
ad
20
oke
~
n-
0
0.1
0
0.1
Time (sec)
1
A
0.2
o.f
0.2
0.3
12000
10000
E8000
16000
5 4000
2000
n
Figure E.86
Time (sec)
Plots of Load, Stroke, Far-Field Strain and Strains from
Notch-Tip versus Time for Specimen M2-LN11.
-270-
.JA
1 OU
AS4/938 Tow Placed, 51 mm Slit
M2-LN12
140, Specimen
Strain Rate: 2 e/min
120
-
-
(n
X
100oo
0
c 80
33
S60
40
+- Load
-- Stroke
20
V00
0.1
Time (sec)
0.2
C
hL_
CI
cIO
"o
MC
LL
".
LL
Time (sec)
Figure E.87
Plots of Load, Stroke and Far-Field Strain versus Time for
Specimen M2-LN12.
-271-
.
AA
160
140
3
120
zloo
2
80
D
60
1
40
20
0
u0
4
I
1
2
3
4
5
1
2
3
Time (sec)
4
5
Time (sec)
f't~f
...1
C
0
76
U..
L
LL
0
Figure E.88
Plots of Load, Stroke and Far-Field Strain versus Time for
Specimen M2-LN13.
-272-
4
.AA
6lbU
AS4/938 Tow Placed, 51 mm Slit
M2-LN14
140 -Specimen
Strain Rate: 2 E/min
120
.3
2100
I2
S80
S60
40
---
Load
20,
-6-
Stroke
I
I
0.1
12000
I
I
Time (sec)
0.2
II
1
A
o.0
.
AS4/938 Tow Placed, 51 mm Slit
Specimen M2-LN14
0000.
C1
Tested at: 2 Emin
8000-
m
t-0
-C)
c-
LL
60004000.
-
-
2000
0
C0
Figure E.89
0.1
Time (sec)
0.2
0.3
Plots of Load, Stroke and Far-Field Strain versus Time for
Specimen M2-LN14.
-273-
-
A_
160
140
3
120
.9
z100
0
2
S80
(
3
rr
S60
1
40
20
V0
1
0
1
0
3
2
Time (sec)
4
5
2
4
5
1
C
CL
cc
U._
V
0
IL
CU
LI
Figure E.90
3
Time (sec)
Plots of Load, Stroke and Far-Field Strain versus Time for
Specimen M2-LN15.
-274-