Filament wound graphite/epoxy samples were immersed in seawater, deionized water, and toluene at room temperature and 80 deg C for 5, 15, and 43 days, and in methanol at room temperature for 15 and 43 days. The percent weight gains and short beam shear strengths were determined after environmental exposure. Samples immersed in deionized water and seawater had higher percent weight gains than those immersed in toluene at room temperature and 80 deg C. The percent weight gains for samples immersed in methanol at room temperature were comparable to those of deionized water and seawater immersed samples. A comparison of percent decreases in short beam shear strengths could not be made due to a large scatter in data. This may indicate defects in samples due to machining or variations in material properties due to processing

Clemons, J. M.

Penn, B. G.

English

NASA Technical Reports Server

NASA
Technical
Memorandum
NASA TM -86553
EFFECTS OF EXTERNAL ENVIRONMENTS ON THE
SHORT BEAM SHEAR STRENGTH OF FILAMENT WOUNDGRAPHITE /EPOXY
(Center Director's Discretionary Fund Final Report)
By B . C . Penn and J. M. demons
Space Science Laboratory and
Materials and Processes Laboratory
Science and Engineering Directorate
July 1986
,{N&S&-Tfl-86553) .;. EFFECTS OF £XfEJBfl&L ,
EKVIBOHHE-HTS CH T-EE SHOfiT E E A H SEEAH
SIBENGfH OF FILAMENT. W O U N D GEfiPHITE/EPOXY .
Center Director's: Discretio.uary Fund Final
Eeport ( N A S A ) • 14 p CSCL j
M 8 6-3 2.5 2 8
Onclas
G3/24 , 44072
fW\SA
National Aeronautics and
Space Administration
George C. Marshall Space Flight Center
MSFC - Form 3190 (Rev. May 1983)
https://ntrs.nasa.gov/search.jsp?R=19860023056 2020-03-20T13:19:04+00:00Z
TECHNICAL REPORT STANDARD TITLE PAGE
1. REPORT NO. 2. GOVERNMENT ACCESSION NO.
NASA TM -86553
4. TITLE AND SUBTITLE
 Effects of External Environments on the
Short Beam Shear Strength of Filament Wound Graphite/
Epoxy (Center Director's Discretionary Fund Final Report)
7. AUTHOR(S)
E.G. Penn and J. M. demons*
9. PERFORMING ORGANIZATION NAME AND ADDRESS
George C. Marshall Space Flight Center
Marshall Space Flight Center, Alabama 35812
12. SPONSORING AGENCY NAME AND ADDRESS
National Aeronautics and Space Administration
Washington, D.C. 20546
3. RECIPIENT'S CATALOG NO.
5. REPORT DATE
July 1986
6. PERFORMING ORGANIZATION CODE
8. PERFORMING ORGANIZATION REPORT «
10. WORK UNIT NO.
1 1, CONTRACT OR GRANT NO.
13. TYPE OF REPORT & PERIOD COVERED
Technical Memorandum
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
Prepared by Space Science Laboratory and *Materials and Processes Laboratory,
Science and Engineering Directorate.
16. ABSTRACT
Filament wound graphite/epoxy samples were immersed in seawater, deionized
water, and toluene at room temperature and 80°C for 5, 15, and 43 days, and in
methanol at room temperature for 15 and 43 days. The percent weight gains and
short beam shear strengths were determined after environmental exposure. Samples
immersed in deionized water and seawater had higher percent weight gains than
those immersed in toluene at room temperature and 80°C. The percent weight gains
for samples immersed in methanol at room temperature were comparable to those of
deionized water and seawater immersed samples. A comparison of percent decreases
in short beam shear strengths could not be made due to a large scatter in data.
This may indicate defects in samples due to machining or variations in material
properties due to processing.
This research^was sponsored by the Center Director's Discretionary Fund
Project (No. 84-5,-^Effects of External Environments on the Failure Mode^and
Mechanical Properties of an Epoxy and Graphite/Epoxy Composite Syster
17. KEY WORDS
Composite materials, environmental effects,
graphite/epoxy composite, seawater,
deionized water, short beam shear
strength, filament wound case
18. DISTRIBUTION STATEMENT
Unclassified — Unlimited
19. SECURITY CLASSIF. (of thl» report)
Unclassified
20. SECURITY CLASSIF. (of thii page)
Unclassified
21. NO. OF PAGES
13
22. PRICE
NTIS
MSFC - Form 3292 (May 1969)
For sale by National Technical Information Service, Springfield, Virginia 22151
TABLE OF CONTENTS
Page
INTRODUCTION 1
EXPERIMENTAL 1
Materials 1
Short Beam Shear Strength 2
Machining of Short Beam Shear Specimens 2
Environmental Testing 2
RESULTS AND DISCUSSION
Percent Weight Gains in the Liquid Environments 2
Analysis of Environmental Effects on the Short Beam Shear Strength ... 2
CONCLUSION 3
REFERENCES 4
PRECEDING PAGE BIA FBJWE&
111
LIST OF TABLES
Table Title Page
1. Composition of Seawater Salt Mixture According to
Manufacturer 5
2. Short Beam Shear Strength After 5 Days of Environmental
Exposure 6
3. Short Beam Shear Strength After 15 Days of Environmental
Exposure 7
4. Short Beam Shear Strength After 43 Days of Environmental
Exposure 8
5. Short Beam Shear Strength After Immersion in Methanol
at Room Temperature 9
IV
TECHNICAL MEMORANDUM
EFFECTS OF EXTERNAL ENVIRONMENTS ON THE SHORT BEAM SHEAR
STRENGTH OF FILAMENT WOUND GRAPHITE/EPOXY
(Center Director's Discretionary Fund Final Report)
INTRODUCTION
Structural components fabricated from fiber reinforced polymers are finding
wide applications in automobiles, commercial and military aircraft, and space systems
because of their high strength, high stiffness, and low weight. In order to take
advantage of these excellent properties, the effects of external environments during
usage on the mechanical properties of composite materials need to be understood.
This is especially true when material failure due to exposure to external environ-
ments can result in loss of life, injury, or high financial losses.
The effects of temperature, moisture, and various organic liquids on the
mechanical properties of epoxy resin reinforced with graphite [1-7] have been studied.
Degradation of mechanical properties most likely occurs due to debonding of the fiber
and matrix and/or cracking of the matrix.
Short beam shear and flexural strength measurements have been used to
examine the effect of environments on the mechanical properties of composite materials."
For example, Rege and Lakkad [8] examined the effect of salt water and distilled
water on carbon and graphite reinforced epoxy. Degradation in salt water was found
to be more severe for the composite systems that were studied. Joshi [9] measured
the short beam shear strengths of unidirectional carbon/epoxy samples immersed in
boiling water. The shear strengths were found to decrease with an increase in the
amount of absorbed moisture.
The purpose of this paper is to report preliminary results of a study directed
at determining the effects of seawater, deionized water, methanol, and toluene on the ~
short beam shear strengths of filament wound graphite/epoxy systems used in the
Space Shuttle.
EXPERIMENTAL
Materials
The dry seawater salt mixture was purchased from Lake Product Co., St. Louis,
Missouri. The composition of this mixture is shown in Table 1. The seawater was
prepared by dissolving 41.95 g of salt mixture in 1000 ml of water as specified by
the supplier.
The SRB-Filament Wound Case (FWC) segments were fabricated using an epoxy
system composed of a mixture of Bisphenol A epoxy and 1,4 butanediol epoxy. The
curing agent was a blend of methylene dianiline and m-phenylene diamine. The
reinforcement was graphite fibers manufactured by Hercules and designated as
A S4W-12K.
Short Beam Shear Strength
The interlaminar shear strength was measured in accordance with ASTM-D
2344-76 short beam shear procedure. An Instron machine with a crosshead speed of
0.05 in./min was used. The size of the transverse specimens was 1.5 x 0.25 x 0.25
in.
Machining of Short Beam Shear Specimens
Large pieces of specimens were cut from actual segments of the SRB-FWC and
machined to dimensions of 1.5 x 0.25 x 0.25 in. This was carried out by cutting the
large pieces of segment into 1.5-in. vertical strips. Each of these were then cut in
the horizontal direction to give pieces having a length of 1.5 in. and width of 0.25 in.
Samples with a thickness of 0.25 in. were prepared by cutting the necessary amount
from the two remaining uncut faces. The machining process is illustrated in Figure 1.
Environmental Testing
Samples machined to dimensions of 1.5 x 0.25 x 0.25 in. as described were
immersed in deionized water, seawater, or toluene at room temperature and 80°C for
5, 15, and 43 days. In addition, samples were immersed in methanol at room tem-
perature for the specified lengths of time. Control samples were also prepared and
heated for the required amounts of time in a desicator placed in an oven. After
environmental exposure the samples were subjected to percent weight gain determina-
tion and short beam shear strength measurements.
RESULTS AND DISCUSSION
Percent Weight Gains in the Liquid Environments
The percent weight gains for filament wound graphite/epoxy samples immersed
in deionized water, seawater, and toluene at room temperature and 80°C for 5, 15,
and 43 days are summarized in Tables 2 through 4. The highest values were obtained
for deionized water and seawater which had percent weight gain values ranging from
0.58 to 1.7 and 0.48 to 1.7, respectively. In comparison, the percent weight gain
values ranged from 0.28 to 0.59 for toluene. Based on these results, deionized water
and seawater are expected to degrade mechanical properties more than toluene.
The percent weight gains of samples immersed in methanol at room temperature
are presented in Table 5. The percent weight gain values are 1.3 and 2.7 for 15
days and 43 days, respectively. This preliminary data indicate that methanol might
have a significant effect on the degradation of mechanical properties since its percent
weight gains are comparable to those of seawater and deionized water. This phenome-
non will be further investigated in future projects.
Analysis of Environmental Effects on the Short Beam Shear Strength
The effects on the short beam shear strengths of immersion in seawater, deio-
nized water and toluene at room temperature and 80°C for 5, 15, and 43 days are
summarized in Tables 2 through 4. Moreover, the effects of immersion in methanol
for 15 and 43 days at room temperature are presented in Table 5. The standard
deviation values, which range from 179 to 615 for the controls and immersed samples,
are too high and variable for determining the quantitative effects of the liquids on
the short beam shear strengths. This trend in standard deviation values might be
due to machining defects or variations in the properties of the composite samples.
These prospective causes will be thoroughly examined in future programs.
CONCLUSION
Graphite/epoxy samples machined from large segments, which were fabricated by
the same process that will be used to make the SRB FWC, were immersed in deionized
water, seawater, and toluene at room temperature and 80°C for 5, 15, and 43 days,
and in methanol at room temperature for 15 and 43 days. The percent weight gains
for samples immersed in toluene was less than those of samples immersed in deionized
water and seawater. The percent weight gains for methanol exposed samples were
comparable to those of seawater and deionized water immersed samples which suggest
that the effects of alcohols and other polar liquid on the mechanical properties of
this composite system should be further investigated.
A comparison of the percent decreases in short beam shear strengths was not
attempted due to the wide data scatter and the small number of samples tested. The
scatter in data might indicate the presence of defects in samples resulting from
machining operations or there might have been variations in the properties of the
filament wound segment. This investigation will continue using this study as a basis.
REFERENCES
1. Browning, C. E., Husman, G. E., and Whitney, J. M.: Moisture Effects in
Epoxy Matrix Composites. In Composite Materials: Testing and Design (Fourth
Conference), ASTM STP 617, American Society for Testing, 1976, pp. 481-496.
2. Springer, G. S., Ed. : Environmental Effects on Composite Materials. Technomic
Publishing Co., Inc., Westport, CT, 1981.
3. Browning, C. E.: Effects of Moisture on the Properties of High Performance
Structural Resins and Composites. Proc. 28th Ann. Tech. Conf. Reinf. Plast./
Com. Inst., SPI, 1973, Sec. ISA.
4. Hertz, J.: Investigation Into the High-Temperature Strength Degradation of
Fiber-Reinforced Composites During Ambient Aging. Tech. Rept. GDCA-D
6B 71-00403, Contract No. NAS8-27435, 1972.
5. Shen, D., and Springer, G. S.: J. Composite Materials, Vol. 11, 1977, p. 2.
6. Gillat, O., and Broutman, L. J.: Effects of External Stress on Moisture
Diffusion and Degradation in a Graphite-Reinforced Epoxy Laminate. In
Advanced Composite Materials-Environmental Effects, ASTM STP 658, J. R.
Vinson, Ed., American Society for Testing and Materials, 1978, pp. 61-83.
7. Browning, C. E.: Polym. Eng. Sci., Vol. 18, No. 1, 1978, p. 16.
8. Rege, S. K. and Lakkad, S. C.: Fibre Science and Technology, Vol. 19,
1983, pp. 317-321.
9. Joshi, O. K.: Composites, Vol. 14, No. 3, 1983, pp. 196-200.
(a)
0.25 IN. {
1.5 IN.
(b)
0.25 IN.
1
-
5IN
-
Figure 1. Machining of specimens for short beam shear strength
measurements. Cutting of 1.5 in. dimension (a), 0.25 in.
width (b) , and 0.25 in. thickness (c).
TABLE 1. COMPOSITION OF SEAWATER SALT MIXTURE
ACCORDING TO MANUFACTURER
Component
NaCl
MgCl2
Na2S04
CaCl2
KC1
NaHCO2
KBr
H3B03
SrCl2
NaF
Percent Composition
59.490
26.460
9.750
2.765
1.645
0.447
0.238
0.071
0.095
0.007
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TABLE 5. SHORT BEAM SHEAR STRENGTH AFTER IMMERSION
IN METHANOL AT ROOM TEMPERATURE
Environment
Methanol
Control
Property Measured
Short Beam Shear Strength (psi)
Standard Deviation
Percent Weight Gain
Number of Samples Tested
Short Beam Shear Strength (psi)
Standard Deviation
Percent Weight Gain
Number of Samples Tested
15 Days
5210
446
1.30
5
5330
186
0.24
4
43 Days
4863
215
2.7
3
5103
315
0.30
5
APPROVAL
EFFECTS OF EXTERNAL ENVIRONMENTS ON THE SHORT BEAM SHEAR'
STRENGTH OF FILAMENT WOUND GRAPHITE/EPOXY
(Center Director's Discretionary Fund Final Report)
By B. G. Penn and J. M. demons
The information in this report has been reviewed for technical content. Review
of any information concerning Department of Defense or nuclear energy activities or
programs has been made by the MSFC Security Classification Officer. This report,
in its entirety, has been determined to be unclassified.
A. J. DESSLERi/
Director, Space Science Laboratory
•6U.S. GOVERNMENT PRINTING OFFICE 1986-631-058/20161
10


Effects of external environments on the short beam shear strength of filament wound graphite/epoxy

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