Supplement to
EFFECT CF PRESTRESSING IN TENSION
OP COMPRESSION ON Tilt MECI-IANICAL
PROPERTIES OF TWO GLASS-FABRIC-BASE
PLASTIC LAMINATES
June 1951
LOAN COPY
Please return to:
Wood Engineering Research
Forest Products Laboratory
Madison 5, Wisconsin
INFORMATION REVIEWED
AND REAFFIRMED
1958
This Report is One of a Series
Issued In Cooperation with the
AIR FORCE-NAVY-CIVIL SUECOMMITTEE
on
AIRCRAFT DESIGN CRITERIA
Under the Supervision of the
AIRCRAFT COMMITTEE
of the
MUNITIONS BOARD
No. 1811-A
UNITED STATES DEPARTMENT OF AGRICULTURE
FOREST SERVICE
FOREST PRODUCTS LABORATORY
Madison 5, Wisconsin
In Cooperation with the University of Wisconsin
Supplement to
EFFECT OF PRESTRESSING IN TENSION OR COMPRESSION ON THE
MECHANICAL PROPERTIES OF TWO GLASS-FABRIC-BASE
PLASTIC LAMINATESBy FRED WERREN, Engineer
Forest Products Laboratory,? Forest Service
U. S. Department of Agriculture
OMM1.11,
Summary
This supplement presents the results of 18 tension tests in which
each specimen was prestressed once prior to the test to failure. Four
different laminates were tested, in both the wet and the dry condition,
and the test results verify the conclusions originally given.
Introduction
From an analysis of the prestress tests of the 181-114 and 143-114
laminates in the basic report, it was suggested that most glass-fabric
plastic laminates would probably act similarly to the 181-114 laminate.
A few supplementary tests of laminates made with entirely different glass
fabrics were considered essential to verify this suggestion.
Experience has shown also that the mechanical properties of such
laminates in the wet condition are usually substantially different from
their properties in the dry condition. Thus, a few prestress tests of
wet specimens were required to indicate the correlation between specimens
in the dry and in the wet condition.
-This progress report is one of a series prepared and distributed by the
Forest Products Laboratory under U. S. Navy, Bureau of Aeronautics
Order No, NAer 01044 and U. S. A ir Force No. USAF-(33-038) 51-4066-E
and 51-4326-E. Results here reported are preliminary and may be
revised as additional data become available.
Maintained at Madison, Wis., in cooperation with the University of
Wisconsin,
Report No. 1811-A -1-
Agriculture-Madison
Testing
Specimens for dry tests were conditioned at 75° F. and 50 percent
relative humidity, and specimens for wet tests were conditioned at 100° F.
and nearly 100 percent relative humidity for 60 days prior to test.
The testing procedures employed were the same as those described
in the basic report, except that a pair of 1-inch metalectric strain gages
were used in testing the dry specimens.
Description of Material
The tensile specimens used in these tests were cut from 1/4-inchthick laminated panels made of either (1) a fine-weave fabric (112-114,
parallel-laminated), (2) a unidirectional fabric (143-114, crosslaminated), (3) a coarse-weave fabric (184-114, parallel-laminated), or
(4) a satin-weave fabric (181-114, parallel-laminated), The fabrication
techniques and method of numbering specimens were as described in the
original report.
Further information regarding the laminated panels is given in
table 1.
Presentation and Discussion of Data
The results of the tension tests are given in table 2. These
values need no further explanation, except that it may be mentioned that
the observed set (col. 9) measured by the 1-inch metalectric gages was
doubled to give a value consistent with those given by the Martens'
mirror gages.
In general, the results of these few tests substantiate the conclusions and expectations outlined in the original report. Since fabrics
with a wide range of properties have been used in these laminates, it is
believed that the conclusions will be applicable to any of the glassfabric nolyestor laminates presently being used for aircraft.
A significant factor observed from the wet tests of the four
laminates ws that the modulus of elasticity after prestress was only
slightly greater than tha secondary modulus from the first run. A comparison of these moduli is readily seen from the ratios given in table 2
(col. 14). For the wet specimens prestressed beyond the secondary proportional limit, the final modulus of elasticity was only 3 or 4 percent
higher than the secondary modulus from the first run, If a similar comparison of moduli is made for the 181-114 laminate in the dry condition, from
data given in the basic report, it is seen that the final modulus after prestressing beyond the prop ortional limit is about 7 percent higher than the
Report No, 1811-A
-2-
secondary value. Although there are too few tests to make any definite
conclusions between the dry and wet conditions for the other three laminates,.
it does appear that the differences between these moduli were less when the
laminate was tested in the wet condition.
It appears, therefore, that in the structural applications of such
laminates where wet conditions must be considered, the secondary values of
modulus of elasticity and proportional limit rill be satisfactory for most
purposes.
The observed set in the wet condition was appreciably less than
the set in the dry condition for the 181-114 laminate. There are not sufficient data to indicate the trends of the other three laminates.
The preceding comments have referred to tensile tests of 181-114
laminate, in which dry tests were made of 1/8-inch laminate from panels Nos.
54 and 70 and wet tests of 1/4-inch laminate from panel No. 24. These
panels were all made by the same procedures and methods, however, and their
properties were considered to have been comparable. Specimens from each of
the other laminates were taken from a single panel.
Conclusions
Results of a few check tests of three additional laminates indicate
that the 181-114 laminate is representative of most glass-fabric polyester
laminates as far as tensile prestress characteristics are concerned. An
exception is the parallel-laminated unidirectional 143-114 laminate. Although these check tests were limited to a single prestress, the conclusions originally stated appear to be applicable to most of these laminates
now being used for aircraft.
Tension tests of four laminates in the wet condition indicate that
the effect of prestressing is similar to that in the dry condition.
The secondary values of proportional limit and modulus of elasticity, arrived at from stress-strain curves of wet-conditioned tensile
specimens, will probably be satisfactory for most design applications,
Report No. 1811-A
-3-
Table l.--Resin content, s ecific gravity ) and average
Barcol hardness for laminated panels. All
panels made of glass fabric with resin 21
:
Panel: Fabric : Direction: Total:Specific: Resin : Barcol
: of plies :number:.gravity :content:hardness
No. :
:
: of :
:
: plies:
:
:
:Percent:
: :
181-114 : Parallel : 23 : 1.79 26 : 1.87
143-114 : Cross 112-114
:
Parallel
:
84 : 1.69 9 :
9 : 1,87
56 : 184-114 : Parallel :
..
:
:
24 1
25 :
:•: : 36.0
: 31.0
: 43.9
: 29.9
:
:
:
:
:
70
70
69
67
-Resin
-Resi n 2 is a high-temperature-setting, low-viscosity
laminating resin of the polyester (styrene-alkyd) type.
Report No. 1811-A
Table 2.--Results of tension tests of four laminates showing the effect df
p reloading on the mechanical properties and observed set
•.
:
Specimen :Thick- : Width : First run
Final run
:Ratio of :Ratio of E
No.
: ness :
:
:
: maximum : of final
•
: Modulus of : Proportional :Maximum :Observed :Modulus:Propor- :Ultimate: applied : run to
••
. elasticity : limit stress :applied : set in : of : tional : stress :stress to: secondary
••
•
:
: stress : 2-inch : elas- : limit :
:ultimate :
E of
:In itiall:Second-:Initial:Second- : : gage
: ticity: stress :
: stress : first run
••
:
3
.
.
: aryl :
: ary:
: length- .
.
•
(1)
:
:
:
(2)
:
(3)
:
:
(4)
:
:
(5)
:
:
(6)
:
.
(7)
:
.
(8)
:
(9)
Inch : Inch • 1000 • 1000 • Psi • Psi : P.s.i. : Inch
: 0.8.1. : p.s.i.:
:
:
:
: (10)
: (11)
:
:
(42)
:
:
(13)
:
(14)
: 1,000 : P.s.i. : P.s.i. : Percent :
: p.s.i.:
.
DRY TESTS
Laminate 143-114, Resin 2 -- Cross-laminated
TC0-9-25-1 : 0.233 : 0.797 : 3,500 : 2,820 : 5,380 •
• 21,540 : 0.00051 : 3,040 : 19,390 : 54,280 : 2 : .233 : .794 : 3,400 : 2,770 : 6,490 : 32,430 : 37,840 : .00126 : 2,920 : 32,430 : 53,840 : Average
3,450 • 2,800 • •5,940 • 32,430 •
39.7 :
70.4
1.08
1.05
59.5 :
77.2 :
1.11
1.10
57.3 :
70.7 :
1.04
1.04
28.8
39.3
49.1
61.7
72.1
83.7
:
:
:
:
:
:
1.07
1.07
1.07
1.05
1.03
1.03
48.1 :
62.9 :
73.6 :
1.04
1.04
1.04
42.0 :
59.0 :
1.06
1.03
57.4 :
1.04
• 54,060 •
Laminate 112-114, Resin 2 -- Parallel-laminated
TAO-9-9-1 : .250 : .796 : 3,060 : 2,450 : 7,040 • • 25,130 : .00100 : 2,730 : 24,120 : 42,210 :
2 : .253 : .793 : 2,930 : 2,300 : 8,970 : 24,920 : 32,900 : .00150 : 2,530 : 22,930 : 42,600 : Average
• 3,000 • • 2,380 • 8,000 • 24,920 •
• 42,400
laminate 184-114, Resin 2 -- Parallel-laminated
TNO-9-56-1 : .234 : .794 : 3,500 : 3,000 : 7,530 : 25,830 : 30,140 : .00083 : 3,130 : 27,990 : 52,640 : 2 : .234 : .793 : 3,460 : 2,970 : 7,540 : 28,020 : 37,720 : .00124 : 3,090 : 28,020 : 53,350 : Average
3,480 • 2,980 • 7,540 : 26,920 • 53,000 •
WET TESTS
Laminate 181-114, Resin 2 -- Parallel-laminated
TB0-9-24-1 : .241 : .799 : 3,040 : 2,680 : 6,230 •
• 12,460 : .00026 : 2,880 : 12,460 : 43,210 : 2 : .241 : .785 : 3,080 : 2,690 : 7,400 •
16,920 : .00038 : 2,890 : 16,920 : 43,080 : 3 : .240 : .787 : 3,070 : 2,570 : 8,470 •
• 21,180 : .00040 : 2,760 : 20,120 : 43,100 :
4 : .241 : .782 : 3,050 : 2,660 : 6,370 •
• 25,470 : .00058 : 2,780 : 25,470 : 41,280 :
5 : .241 : .782 : 3,030 : 2,700 : 6,370 : 25,470 : 29,710 : .00062 : 2,790 : 24,410 : 41,230 :
6 : .243 : .777 : 2,880 : 2,300 : 6,360 : 27,540 : 33,900 : .00095 : 2,360 : 26,480 : 40,520 : Average
: 3,020 • 2,600 : 6,870 • 26,500 • 42,070 •
Laminate 143-114, Resin 2 -- Cross-laminated
TCO-9-25-3 : .235 : .785 : 2,570 : 2,230 : 5,420 : 20,600 : 21,680 : .00091 : 2,320 : 20,600 : 45,o5o : 4 • .237 : .780. 2,660 : 2,260 : 5,410 : 21,640 : 27,050 : .00108 : 2,360 : 21,640 : 43,000 : 5 • .236. .778. 2,660 : 2,440 ! 5,450 : 31,590 : 32,680. .00115 • 2,530 : 32,680 : 44,390 :
Average
2,630 : 2,310 5,430 - 24,610 • 44,150 • Laminate 112-114, Resin 2 -- Parallel-laminated
TAO-9-9-3 ; .253 : .780: 2,490 : 2,300 : 7,090 •
• 15,200 : .00048 : 2,430 : 15,200 : 36,180 :
5 : .256: .781: 2,300 : 2,090 : 7,000 : 19,010 : 21,010: .00088 : 2,160 : 19,010 : 35,610 : :
:
:
:
:
:
:
:
•
•
*
Average
2,400 • 2,200 - 7,040 • 19,010 • 35,900 • Laminate 184-114, Resin 2 -- Parallel-laminated
TNO-9-56-3 : .237 : .790 : 2,990 : 2,620 : 7,480 : 22,430 : 26,710 : .00097 : 2,730 : 22,430 : 46,570 : 1Valuee based on initial straight portion of stress-strain curve.
2Values based on second straight portion of stress-strain curve.
-Values from the six dry tests are double those actually observed on a 1-inch gage length, in order to be on a
basis comparable with the other tests.
ZM 87276 F