FACTORS AFFECTING THE
STRENGTH OF IPAPREG
EFFECT Of MOISTURE ON CERTAIN
STRENGTH PROPERTIES OF PAPREG
Inforntatien–PavicazucLand–Leaffirmcd
Merreh-1946-
INFORM,'
AND
1.PYPD
No. 1521-P
1
1011141
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FOREST PRODUCTS LABORATORY
MADISON S. WISCONSIN
UNITED STATES DEPARTMENT OF AGRICULTURE
FOREST SERVICE
Coo peration with the University of Wisconsin
FACTORS AFFECTING THE STRENGTH OF PAPREG 1, a
Effect of Moistures on Certain Strength Properties of Papreg
By
H. R. MEYER, Engineer
and
E. C. O. ERICKSON, Engineer
Forest Products Laboratory 14. Forest Service
U. S. Department of Agriculture
Summary
This report presents the results of approximately 750 tests made at normal
temperatures to determine the effect of moisture on certain tensile, compressive, flexural, and bearing properties of both parallel- and cross-laminated
papreg, 1/8 inch in thickness.
In general, a decrease in strength properties accompanied an increase in moisture. More specifically, exposure to 80° F. and 97 percent relative humidity
decreased the modulus of elasticity in tension and compression approximately
30 percent based on normal exposure (75° F. and 50 percent relative humidity).
A similar comparison for the proportional limit in tension and compression indicated a decrease of approximately 6o percent. Decreases of lesser magnitude
with increase in moisture content were found for the same exposure comparisons
in static bending and bearing.
1This report is one of a series of progress reports prepared by the Forest
Products Laboratory relating to the use of wood in aircraft. Results here
reported are preliminary and may be revised as additional data become
available. Original report published in January 1945.
2A laminated paper plastic made by the Forest Products Laboratory (Improved
(Standard -- June 1943).
•This report is the third in a series of reports presenting the effect of aircraft service conditions on certain strength properties of papreg.
li maintained at Madison, Wis., in cooperation with the University of Wisconsin.
Report No. 1521-B -1-
Agriculture-Madison
Introduction
This investigation was undertaken to obtain data on the effect of moisture on
certain of the mechanical properties of paper plastic laminates, for which
relatively little data are available.
The data herein reported, although somewhat limited in scope, are believed to
be indicative of the moisture-strength characteristics of this type of material.
The first portion of this report presents the results of tests on specimens
taken from panels with protected edges after exposure to various relative
humidities.
The results of pilot tests on specimens immersed in water are shown in appendix A. These results, appended primarily to record the moisture-strength data
thus obtained, may also serve to direct the course of other investigations.
Appendix B presents the results of a few tests to show the dimensional behavior
of papreg in several humidities.
Test Material
The test material, identified as Improved Standard -- June 1943, was made by
the Forest Products Laboratory from a commercial Mitscherlich black spruce
sulfite pulp and a phenolic type thermosetting resin (BV-16526). The resin
content of the impregnated paper was 36.3 percent and the volatile content,
4.5 percent. The preparation of the papreg was identical to that described in
Forest Products Laboratory Report No. 1521. 5 Specific gravity was 1.40, based
on weight and volume after conditioning at 75° F. and 50 percent relative humidity. Test material consisted of both parallel-laminated and cross-laminated flat panels, approximately 12 inches square and 1/8 inch in thickness.
Selection and Preparation of Test Panels
The papreg panels used for the experimental work in this investigation were
taken from groups I and II (parallel- and cross-laminated material, respectively), described in Forest Products Laboratory Report No. 1521. Twelve
panels were taken from group I and seven from group II. All panels were
trimmed to approximately 11 inches square, to provide square, clean edges,
' which were sealed immediately with two coats of a heavy aluminum paint to retard moisture movement through these edges thereby simulating service conditions wherein exposed edges will presumably be protected.
Factors Affecting the Strength of Papreg. Some Strength Properties at
Elevated and Subnormal Temperatures.
Report No. 1521-B
-2-
The panels were divided into lots, numbered 1 to 5 inclusive. Each lot
consisted of two panels from group I and one panel from group Lots 4 and
5 were each provided with an additional panel from each group in which 1/4and 1/8-inch holes were drilled for subsequent bearing tests. These holes
were fitted with snug-fitting brass bolts with washers and brass nuts drawn
tight to approach service conditions.
Following preparation, individual panels were weighed and measured to provide
the basis for determining subsequent weight and dimensional changes.
Conditioning of Panels
The various lots of prepared panels were distributed in several automatically
controlled constant temperature and relative humidity rooms (used also to condition wood specimens) as follows:
Lot 1 -- 80° F. and 30 percent relative humidity
Lot 2 -- 75° F. and 50 percent relative humidity
Lot 3 -- 80° F. and 80 percent relative humidity
Lot 4 -- 80° F. and 97 percent relative humidity
Lot 5 -- immersed in distilled water at 75° F.
For purposes of discussion these conditioning media are classified as follows:
dry (30 percent relative humidity), normal (50 percent relative humidity),
humid (80 percent relative humidity), and wet (97 percent relative humidity)
and soaked (immersed in water).
All panels were conditioned for approximately 100 days. During this conditioning period, individual panels were weighed periodically to provide weight
increase, or moisture gain, data. In this report the gain in weight is assumed
to be equal to the gain in moisture.
Preparation of Test Specimens
At the conclusion of the conditioning period, the panels in each lot were cut
as shown in figure 1 to provide specimens from the lengthwise and crosswise
directions, that is, parallel and perpendicular to the machine direction (fiber
grain) of the paper in the parallel-laminated panels but parallel and perpendicular to the edge of the panel in the cross-laminated panels.
The following numbers of specimens were provided for tension, compression,
bending and bearing tests, respectively: six lengthwise and four crosswise
specimens from parallel-laminated panels and five specimens (three lengthwise
and two crosswise, or vice versa) from the cross-laminated panels.
Report No. 1521-B
-3-
Fewer specimens from a greater number of panels were not taken because previous
investigations using this method showed but little variation among panels as
indicated by the coefficient of variation of approximately 4 percent for ultimate strengths.
The type, dimensions, and cutting of the specimens conformed to Federal Specification for Plastics, Organic; General Specifications (Method of Tests),
L-P-406 1 December 9, 1942.
Conditioning of Test Specimens
Immediately after preparation, all specimens, with the exception of those immersed in distilled water, were returned to the respective conditioning atmosphere of the panels from which they originated for at least 24 hours prior
to testing. This procedure was employed to compensate for any moisture loss
incurred in preparation during which the material was exposed to a relatively
dry atmosphere. The specimens cut from panels immersed in water were wrapped
in wet cloths and placed in the 80° F. and 97 percent relative humidity room.
This procedure was followed in order to minimize the possibility of excessive
swelling of the unsealed edges of these specimens, a condition which might have
resulted upon re-immersion.
Conditioned specimens were placed, a few at a time, in a closed container prior
to testing. Those specimens conditioned between wet cloths were placed in a
container intact with the wet cloths. Except for the few minutes required to
weigh and measure, specimens were not exposed to the test room atmosphere until
placed in a testing machine.
Testing Procedures
All tests were conducted at room temperatures and humidities of approximately
78° F. and 6o percent relative humidity according to procedures outlined in
the Federal Specification L-P-406.
Compression tests to determine ultimate stress were conducted on pairs of specimens 1 inch wide by 1/2 inch long, spaced parallel and 1 inch apart and loaded
simultaneously; while the modulus of elasticity, proportional limit, and yield
strength properties were determined by testing individual specimens 1 inch
wide by 4 inches long as laterally supported columns.
The pertinent details of the tension, compression, bending, and bearing tests
were identical to hose described in the appendix of Forest Products Laboratory
Report No. 1521-A..2
F actors Affecting the Strength of Papreg. The Effect of Accelerated Weathering on Certain Mechanical Properties of Papreg.
Report No. 1521-B
-4-
Behavior During Conditioning
The time-moisture gain relationship of the panels during the conditioning
period of approximately 100 days is shown in figure 2. The data for the panels
conditioned in 30 percent relative humidity are not shown because the moisture
gain was small in magnitude -- approximately 0.1 percent. This indicated that
the moisture content of the panels after molding was in approximate equilibrium
with 30 percent relative humidity conditions at 800 F. The magnitude of this
moisture content was not determined. In fact, the term, moisture content, is
not strictly applicable to papreg because the amount of moisture included in
the 4.5 percent total volatile is not known. In the absence of a standard
method for determining the moisture content of papreg, it is believed that a
close approximation was obtained by plotting the percent increase in weight at
equilibrium moisture for identical companion panels against the corresponding
relative humidity. Extrapolation to zero percent relative humidity indicated
a decrease in weight of less than 1/2 percent between 30 and zero percent relative humidities. Hence, from this analysis, it appears that the moisture content at 30 percent relative humidity is less than 1/2 percent.
Panels exposed to 50 percent relative humidity reached apparent equilibrium
moisture content after approximately 100 days. Those conditioned in 80 and 97
percent relative humidities reached 85 and 90 percent apparent moisture equilibrium, respectively, during this period, based on the subsequent behavior of
identical companion panels retained in these atmospheres until the apparent
equilibrium moisture content was reached. These data indicated that 1/8 inch
thick papreg requires from 200 to 250 days of conditioning to reach the apparent equilibrium moisture content at 80 0 F. and 97 percent relative humidity.
The rate of moisture absorption could be further retarded by the application of
a surface coating and an improvement in the method of sealing the edges.
Results of Tests
Maximum, minimum, and average values for a specified number of tests of each
of the properties of parallel- and cross-laminated papreg for the five mois,
ture conditions are presented in tables 1 and 2. All property values are
based on the original thickness dimension of the papreg before conditioning
and the width dimension at the time of test.
Figures 3 and 4 show the moisture-strength relationships for parallel- and
cross-laminated papreg. The results of tests on lot 5 (soaked panels) are
presented in appendix A with the results obtained from exploratory tests on
soaked specimens of identical material. A comparison of the curves for
parallel-laminated papreg (fig. 3) with those for cross-laminated papreg
(fig. 4) indicates that, in general, a decrease in the strength properties
accompanied an increase in moisture.
Report No. 1521-B -5-
The relationship between the percent increase in moisture and the strength
properties of lots 1, 3, and 4 expressed as a percentage of lot 2 (75° F., 50
percent relative humidity) is shown graphically in figures 5 and 6. It may be
noted that the curves (figs -. 5 and 6) for tensile properties, with the exception of those of ultimate stress, follow the same sequence shown in the compression properties. More specifically, the modulus of elasticity is least
affected by moisture, and the proportional limit most. Figures 5 and 6 further
indicate that parallel-laminated and cross-laminated materials are, in general,
equally affected by identical increases in moisture.
A few tests were made to determine the effect of moisture on the hardness of
papreg by the standard Rockwell indentation test. The results indicate a decrease in hardness (M scale) with an increase in moisture. The values ranged
from 108 for lot 1 (30 percent relative humidity) to 65 for lot 4 (97 percent
relative humidity).
Observations made to determine the change in the thickness dimension under
various moisture conditions indicated that the ratio of the percent increase
in moisture to percent increase in thickness was approximately unity.
A few tests in plate shear 2 conducted on 5 inch square parallel- and crosslaminated specimens from lot 4 (wet) indicated a modulus of rigidity of
677,000 pounds per square inch and 707,000 pounds per square inch, respectively. Results of tests from a comprehensive investigation2. at normal temperature (75° F., 50 percent relative humidity) on material fabricated to be
identical to that of lot 4, show values of 909,000 and 887,000 pounds per
square inch, respectively. This indicates a loss in shear modulus of approximately 20 to 25 percent due to a moisture increase of approximately 10 percent.
A comparison of the average bearing strength of specimens having bearing holes
drilled and fitted with bolts before conditioning to 80° F. and 97 percent
relative humidity, with specimens having bearing holes drilled after conditioning are shown in table 3.
In table 3, it may be noted that the stresses for specimens with the bearing
holes drilled and fitted with bolts before conditioning were, in general,
higher than those for specimens in which the bearing holes were drilled after
conditioning. A similar comparison of bearing tests conducted on specimens
from panels in lot 5 (immersed in water) indicates that the stresses for specimens in which the bearing holes were drilled after conditioning were, in
general, the higher. The reason for these differences is not evident from the
limited number of tests.
'Forest Products Laboratory Report No. 1301, "Method of Measuring the Shearing
Moduli in Wood."
F orest Products Laboratory Report No. 1319, revised, "Strength and Related
Properties of Forest Products Laboratory Laminated Paper Plastics (Papreg)
at Normal Temperature."
Report No. 1521-B
-6-
Typical stress-strain curves of tension, compression, and bearing tests, as
well as load-deflection curves for flatwise static bending tests for both
parallel- and cross-laminated papreg, are shown in figures 7 to 10, inclusive.
All curves are based on actual load-deformation data for individual specimens
having properties in close agreement with the average of the group.
Deformations in the tensile tests were observed to approximately 0.01 inch per
inch strain and also immediately before fracture. The broken line portion of
the stress-strain curves indicates that portion for which deformations were not
observed.
Conclusions
In general, a decrease in the strength properties of papreg accompanied an increase in moisture.
Further, the percentage decrease in strength properties based on conditioning
at 75° F. and 50 percent relative humidity was essentially the same for both
parallel-laminated and cross-laminated material.
With the exception of the ultimate strengths, the tensile and compressive
strength properties exhibited like reductions when the moisture content was increased above normal (equilibrium with 75° F. and 50 percent relative humidity).
Both ultimate strengths decreased when the moisture was increased beyond normal,
but the percentage reduction in compressive strength was approximately two to
three times that produced on the tensile strength for a given increase in moisture.
The maximum decreases in static bending and bearing strengths due to moisture
increases were less than those in tension and compression.
Further investigations at other humidities are recommended to determine the
range of moisture-strength relations for paper plastic laminates.
APPENDIX A
Pilot tests were conducted on standard specimens of papreg soaked in distilled
water at ordinary room temperatures to determine quickly the magnitude of
moisture effects on the strength properties and to guide the planning of the
first portion of the experiments here reported. Hence, the pilot-test results
differ from those presented in the main body of the report, which were obtained
from specimens cut from large panels conditioned in moist air.
Report No. 1521-B
-7-
Test Material
The test material consisted of additional 1/8 inch thick parallel-laminated and
cross-laminated panels identical to those described in the fore part of this
report.
Preparation of Specimens
The papreg panels used in this exploratory investigation were also taken from
the groups I and II described in the previously referred to Forest Products
Laboratory Report No. 1521. Twenty panels were taken from group I and 12
from group II.
Tension, compression, and static bending specimens were cut from these panels
as shown in the cutting diagram in figure 11. This diagram provided specimens
from the lengthwise and crosswise directions. The selection and grouping of
the specimens are shown in the table in figure 11. Those specimens that are
not shown in the selection table were used in tests of other service conditions.
The type, dimensions, and cutting of the specimens were identical to those
previously described.
Conditioning of Specimens
Each group of specimens was weighed and measured and then conditioned as
follows:
Group A -- 17 days at 75° F. and 50 percent relative humidity. (Controls, at
apparent equilibrium moisture content.)
Group 12. -- 2 days' immersion in distilled water at ordinary room temperatures.
Group --
4 days' immersion in distilled water at ordinary room temperatures.
Group d -- 8 days' immersion in distilled water at ordinary room temperatures.
Group g. -- 24 hours' heating at 122° F. in an electric oven.
Testing Procedures
Specimens were tested at normal room temperatures and humidities immediately
after conditioning. The procedures employed were identical to those described
in the body of this report.
Report No. 1521-B
-8-
The specimens conditioned at 122° F. were cooled to room temperature in a
desiccator before being tested.
Results of Tests
Table 4 presents average values for tensile, compressive, and static bending
properties of both parallel- and cross-laminated papreg for specimens (1) immersed in water -- groups b., r,„ and d, (2) heated at 122° F. -- group 2.1 and
(3) conditioned at 75° F. and 50 percent relative humidity -- group g. An inspection of the results reveals that, with respect to group a (75° F., 50 percent relative humidity), the corresponding results for groups h, gl and d
(immersed), show a definite decrease in all of the properties reported, while
group e (heated) shows a decrease in 65 percent of the properties reported
and an increase in the remaining 35 percent of the properties reported. The
magnitude of the decreases in the immersed group increased with the immersion
time, while in the heated group both the decreases and increases were relatively small. All values of the heated group, except one, however, were
higher than those in group b (2 days' immersion).
Moisture-strength relations for immersed specimens of parallel-laminated papreg, tested lengthwise, are presented graphically in figure 12. Property
values for specimens conditioned at 75° F. and 50 percent relative humidity
are indicated. Also indicated for comparison are the corresponding property
values for specimens taken from panels with sealed edges following 98 days'
immersion. These specimens were described as lot 5 in the body of this report.
The values of the strength properties for the papreg conditioned at 75° F. and
50 percent relative humidity are not joined with those for the immersed papreg
because the conditioning was not comparable.
The variation shown in figure 12 for the increase in moisture between ultimate
compressive strength and other compressive properties is believed to be due
to the difference in surface areas of the two specimen sizes.
The tensile and compressive properties of the specimens immersed for 8 days
were essentially in'agreement with those of specimens taken from immersed
panels (lot 5). Although the total moisture content of the two types of
specimens differed but slightly, a considerable difference in the moisture
distribution in each was obvious. Specimens from lot 5 (whole panels immersed) were uniform in thickness, whereas immersion of actual specimens
brought about an edge swell and a variable increase in thickness. The degree
of variability varied with immersion time. This progressive edge-swelling was
at first believed to cause a fiber damage that would be reflected in the
strength values and exclude the use of immersed specimens in a quick determination of the moisture-strength index. The agreement in the properties
mentioned previously, however, did not substantiate this belief.
In contrast to the data for tension and compression it should be noted that,
in static bending, the modulus of rupture and the modulus of elasticity of
Report No. 1521-B
-9-
specimens immersed for 8 days did not agree with those cut from the panels of
lot 5. The elastic modulus of specimens from panels immersed 98 days (lot 5)
was greater than that for specimens immersed for 8 days. Similarly the elastic modulus of specimens immersed for 8 days was greater than that of specimens immersed for 6 days. It was thought that this behavior might be due to
the use of the original thickness, rather than the thickness at test, in the
computation of the elastic modulus. Calculations of the modulus of elasticity
based on the swollen thickness dimensions, however, gave lower values, as
would be expected but these recomputed values for the higher moisture content
again were greater than those for the preceding lower moisture content. This
departure from the trends indicated in tension and compression will require
further investigation before the indicated trend in static bending can be
confirmed.
Extensive deductions relative to the comparative behavior of papreg immersed
in water (fig. 12) with that subjected to moisture in vapor form (fig. 2) are
to be avoided, since only when papreg was subjected to moisture in vapor form
were tests made when the papreg was at approximate moisture equilibrium.
APPENDIX B
In the absence of data on the dimensional stability of papreg under various
humidities, the results of an exploratory investigation made to determine the
effect of moisture on the length, width, and thickness dimensions of both
parallel-laminated and cross-laminated papreg are herewith presented. The
results should be viewed as indicative only of what may be expected of papreg
under certain moisture conditions, since the scope of the investigation was
limited.
Test Material
The test material consisted of both parallel- and cross-laminated panels,
approximately 12 inches square in 1/16- and 1/8-inch thicknesses, which had
been stored at ordinary room temperatures and humidities for 2 months after
molding. The composition and manufacturing details of the papreg were identical to those referred to in the fore part of this report. The 1/16-inch thick
panels were molded from approximately 35 sheets of treated paper at the same
temperature, pressure, and curing time as indicated for the 1/8-inch panels.
Preparation of Test Specimens
One parallel- and one cross-laminated panel in both the 1/16- and 1/8-inch
thicknesses were each cut into four specimens approximately 5-1/2 inches
square. Four flat-head steel reference pins were driven in prebored holes in
Report No. 1521-B
-10-
each specimen in the positions shown in figure 13. The flat head of each
reference pin contained a small hole whose diameter was the same as that of
the gage holes found on the gage bar (4-inch length) for a Berry strain
gage. The edges of all specimens were sealed with two coats of a heavy aluminum paint to retard the movement of moisture through these edges.
Conditioning of Test Specimens
Test specimens were heated in an oven for 24 hours at a temperature of 122° F.
After cooling to room temperature in a desiccator, each specimen was weighed
and measured. The length and width dimensions were taken between the small
holes in the reference pins. The thickness was measured at the five places
indicated in figure 13 by an X.
One parallel- and one cross-laminated specimen of both thicknesses were then
placed in each of the following constant temperature and relative humidity
roams: 80° F. and 30 percent relative humidity, 80° F. and 65 percent
relative humidity, 80° F. and 97 percent relative humidity, and -25° F.
Testing
The length and width dimensions were measured with a 4-inch gage length
Berry strain gage (magnification factor of approximately 5) equipped with a
0.001-inch dial gage. Ten repeated readings of the length and width, respectively, were taken to minimize any effect caused by uneven seating of the gage
points within the hole of the reference pins.
The thickness at the five designated locations was measured with a micrometer
caliper equipped with a 0.001-inch dial gage.
Measurements were taken at various intervals while the specimens were approaching moisture equilibrium.
All operations were conducted within the respective conditioning rooms with
the exception of the room at -25°F. Due to the erratic behavior of ordinary
gages at subnormal temperatures, specimens were removed from the -25° F. roam,
one at a time, and measured at ordinary room temperatures immediately after
removal.
Results
The results of these exploratory tests indicate that papreg is dimensionally
stable at 80° F. and 30 percent relative humidity and at -25° F. The
Report No. 1521-B
-11-
dimensional changes at 80° F. and 65 and 97 percent relative humidities are
shown in table 5.
In the parallel-laminated material, the length dimension (fiber-grain or
machine direction) shows the least increase, while the thickness is the
greatest. The increase in width is from 3 to 5 times greater than that in
length. As would be expected, the increases in the length and width dimensions of the cross-laminated material do not differ greatly. It may also be
observed that the percent change in weight is approximately equal to that in
thickness in all instances, except in the 1/8-inch thick parallel-laminated
material in 65 percent relative humidity. No explanation can be advanced for
this lack of agreement.
It may be noted further that the behavior of the 1/16-inch material agrees
well with that of the 1/8-inch material, except as discussed previously.
In view of the limited number of tests, further investigation is desirable to
determine the range of the dimensional changes of this material under various
humidities.
Report No. 1521-B
-12-
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Table 3.--Average results of tests to compare the bolt-bearing strength of
papreg when the bearing holes are drilled before and after conditioning to 80° F. and 97 percent relative humidity
Direction of grain relative to the length of specimen
Parallel
Perpendicular
:Lengthwise and crosswise
Casey
: Ultimate: Bearing :Ultimate: Bearing :
: bearing :stress at:bearing :stress at :
: stress :4 percent: stress :4 percent :
:deforma:deforma- :
: tion of :
: tion of :
: hole
•
: hole
:
: diameter :
:diameter :
Ultimate : Bearing
bearing : stress at
stress
: 4 percent
deforma: tion of
hole
:
: diameter
: Lb. per : Lb. per : Lb. per: Lb. per :
: sq. in. : sq. in. : sq. in.: sq. in. :
Lb. per :
sq. in. :
Lb. per
sq. in.
: 22,400 : 12,920 : 19,810 : 11,490 :
22,800
12,690
24,630: 12,730 : 22,190 : 12,240
21,460
11,920
1.06
1.06
1/8 inch diameter holes
A
B:
Ratio:
A/B:
.91 :
1. 02 :
.89 :
.94
:
1/4-inch diameter holesa
A
B
: 17,800 : 13,890 : 17,180 : 14,000 : 17,700
13,860
: 21,700 : 17,880 : 19,350 : 15,000 : 18,420
14,850
•
Ratio:
A/B•
82 •
78 •
89 •
93 :
.96
.93
-Case A: Bearing holes drilled in the specimens after conditioning.
Case B: Bearing holes drilled in the panels and fitted with bolts before
conditioning.
Average values from 4 - 6 tests.
a
Average values from 1 - 5 tests.
Report No. 1521-B
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Table 5.--Percent increase in dimensions of papreg from dry
condition (24 hours at 122° F.) to equilibrium
at 65 and 97 percent relative humidities
Condition
:
:
:
Type of papreg : :
:
80° F.
65 percent relative :
humidity
:
:
Dimension
:
80° F.
97 percent relative
humidity
Dimension
:Length:Width :Thick-:Weight:Length:Width :Thick-:Weight
.•
.
: ness :
: ness :
:
:
•
•.
1/8-inch thick material
.
:
.
.-
.
•
•.
.•
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.11 : .09 : 1.3 : 1.6 : .27 : .22 : 9.7 : 9.3
Cross-laminated
•
1/16-inch thick material
Parallel-laminated : .07 : .21 : 1.4 : 1.8 : .09 : .48 : 9.8 : 9.7
Cross-laminated
Report No. 1521-B
.11 : .12 : 1.5 : 1.9 : .22 ; .18 ; 10.5 ; 9.6
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COMPRESSION (EDGE WL5E)
LEGEND:•-COND/TIONED AT 80'F- 30 PERCENT RELATIVE HUMIDITY (LOT 0—
0-CONDITIONED AT 75' F. 50 PERCENT RELATIVE/ION/0/TV (LOT 2)
O-CONDITIONED AT 80'P - 80 PERCENT RELATIVE HUMIDITY (LOT 9)
• - CONDITIONED AT 00' F- 97 PERCENT RELATIVE HUMIDITY (LL2T4,1_ 4,000
NOTE: SPECIMENS WERE PREPARED FROM H-BY H-BY ,i---INCH PANELS,(WITH
5EALED EDGES)WHICH HAD BEEN CONDITIONED FOR APPROXIMATELY /00 DAY5-EACH PO/NT REPRESENTS THE AVERAGE
4600
RESULT OF 5OR 6 TESTS- .1
• .
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ELONGATION
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a
a
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40
60
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INCREASE /N MOISTURE (PERCENT)
STATIC 8£ND/N6
/0.0
50
20
40
60
INCREASE IN MOISTURE (PERCENT)
0.0
BEARING (a-- /NCH P/N)
Figure 3.--Moisture-strength relationship of parallel-laminated
papreg (Improved Standard - June 1943) in the lengthwise direction.
57895
ir
36
3,600
1
I
LEGEND :-1
1I
1
i
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Q-CONDITIONED AT 7.71. - - 50 PERCENT RELATIVE HUMIDITY (LOT2)__. 3,200
CI-CONDITIONED AT 80 . E- 80 PERCENT RELATIVE HUMIDITY (LOTS)
• -CONDITIONED AT 80',‘.- - 97 PERCENT RELATIVE HUMIDITY (LOT4)
/VOTE:- SPEC/IVENS WERE PREPARED FROM/I-BY //-.84-INCH PANEL5,(W/TII
2,600
SEALED EDGES) WHICH HAD BEEN CONDITIONED FOR APPROXFMAYFLY /00 DAYS.
POINT REPRESENTS THE AVERAGE
RESULT OF 5 OR 6 TESTS.
2,400
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STATIC BENDING
•
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8.0
/00
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2.0
40
/A/CREASE. /N M0/57URE (PERCENT)
BEARING (-a-INCH PIN)
Figure 4.--Moisture-strength relationship of cross-laminated
papreg (Improved Standard - June 1943).
Z M
57896 F
60
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m ..
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INCREASE /N MOISTURE (PERCENT)
4.0
STAT/C BEND/NO
IM
11
n 1111
44 60
70
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BEAR/NG(a—/NCH PIN)
Figure 5.--Moisture-strength relationship of parallel-laminated
papreg (Improved_ Standard - June 1943) in the lengthwise
direction, expressed as a percentage of the streugtli properties at 75° F. and 50 percent relative humidity.
Z M 5 78 9 7 F
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o-CONDITIONED AT 80°F- 80 PERCENT RELATIVE HUMIDITY (LOT 3)
a-CONDITIONED AT 50"F- 97 PERCENT RELATIVE HUMIDITY (LOT 4)
NOTE: SPECIMENS WERE PREPARED FROM I/-BY II-BY k-INCH PANELS
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Figure 6.--Moisture-strength relationship of cross-laminated
papreg (Improved Standard - June 1943) expressed as a percentage of the strength properties at 75° F. and 50 percent
relative humidity. Points show changes based on average
results of the test data whereas curves show changes based
on the average relationship among the several humidities.
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LEGEND,
(A)-CONDITIONED AT 80-f-30 PERCENT RELATIVE HUMIDITY (LOT I)
( a) COvO(TIONED AT 7_5"F-50PERCENT RELATIV HUMIDITY (LOT 2)
(C)-CONDITIONED AT 80T-80 PERCENT RELATIVE HUMIDITY (LOT 3)
(D) CONDITIONED AT 807:- 97 PERCENT RELATIVE HUM/0/ TY (LOT 4-)
0-IMMERSED IN DISTILLED WATER AT 757: ( LOT 5)
NOTE:SPECIMEN WERE PREPARED FROM H- BY //-84-INCH
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Figure 7.--Typical tensile stress-strain curves for paoreg
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immersion conditions.
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Figure 8.--Typical flatwise flexure load-deflection curves for papreg
(Improved Standard - June 1943) under various humidity and immersion
conditions. Specimens were 1 by 1/8 by 4-1/2 inches. Span was
2-1/2 inches. Center loading.
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(C) DO/YD/T/ONED AT 80T- 80 PERCENT RELATIVE HUMIDITY (L07-3,)
(D)CONDITIONED AT BOP- 97 PERCENT RELATIVE HUMIDITY (LOT4)
(E) IMMERSED IN DISTILLED WATER AT 75 .P- (LOT 5)
NOTE:5PEC/MEN5 WERE PREPARED FROM //BY N-84-INCH
PANEL5(WITH _SEALED EDGE5)WHICH HAD BEEN CONDITIONED
FOR APPROX/AfATELY /00 DAYS
THE END PO/NT OF EACH CURVE /5 ARBITRARY AND
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Figure 9.--Typical compression (edgewise) stress-strain curves for
papreg (Improved Standard - June 1943) under various humidity and
immersion conditions. Specimen was 1 by 1/8 by 4 inches and was
tested as a laterally supported column.
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Figure 10.--Typical-bearing stress-hole deformation curves for
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and immersion conditions. Specimen 15/16 inch wide by 1/8
inch thick; hole diameter 1/8 inch; edge distance 2.5 hole
diameters.
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determination of dimensional stability of parallel- and
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