The effect on the flexural properties of a glass/epoxy composite of immersion in deionized water or seawater at 0, 25, and 80 C for 451 hr was examined. The percent weight gain at 0 and 25 C was low (0.06 to 0.17 percent) and there was no significant change in the flexural properties for these environmental conditions. At 80 C there was a decrease in the flexural strength of 17 and 20 percent in seawater and deionized water, respectively. This is a comparison to control samples exposed to 80 C heat alone. These decreases were found to be nearly reversible once the samples were dried. Optical microscopy did not reveal cracking of the matrix. The flexural modulus was essentially unaffected by exposure to deionized water and seawater at 80 C

Clemons, J. M.

Daniels, J. G.

Goldberg, B. G.

Ledbetter, F. E., III

Penn, B. G.

Semmel, M. L.

White, W. T.

English

NASA Technical Reports Server

NASA
Technical
Memorandum
J
NASA TM -86544
EFFECTS OF SEAWATER AND DEIONIZED WATER AT
0 TO 80°C ON THE FLEXURAL PROPERTIES OF
A GLASS/EPOXY COMPOSITE
(Center Director's Discretionary Fund Final Report)
E . G . Penn, J. G. Daniels, F. E. Ledbetter, III,
M. L. Semmel, E . G . Goldberg, W. T. White, and
J. M. demons
Space Science Laboratory
Science and Engineering Directorate
March 1986
(NASA-TM-8654U) EFFECTS OF SEA8A1ER AND N86-24758
DEIONIZED H A T E B AT 0 TO 80 CEG C ON THE
FLEXOBAL PROPERTIES OF A GIASS/EPCXY
COMPOSITE ( N A S A ) 11 p HC A 0 2 / H F A01 Ufldas
CSCL 11D G3/24 13050
WASA
National Aeronautics and
Space Administration
George C. Marshall Space Flight Center
MSFC - Form 3190 (Rev May 1983)
https://ntrs.nasa.gov/search.jsp?R=19860015287 2020-03-20T15:22:07+00:00Z
TECHNICAL REPORT STANDARD TITLE PAGE
NASA TM - 86544
4 TITLE AND SUBTITLE Effects of Seawater and Deionized Water
at 0 to 80°C on the Flexural Properties of a Glass /Epoxy
Composite *
1 . AUTHOR(S)
See Below
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, B.C. 20546
5 REPORT DATE
March 1986
6. PERFORMING ORGANIZATION CODE
8. PERFORMING ORGANIZATION REPORT ft
10. WORK UNIT NO.
11. CONTRACT OR GRANT NO.
13. TYPE OF REPOR'i & PERIOD COVERED
Technical Memorandum
14. SPONSORING AGENCY CODE
IS. SUPPLEMENTARY NOTES
Prepared by Space Science Laboratory, Science and Engineering Directorate.
16. ABSTRACT
The effect on the flexural properties of SL glass /epoxy composite of immersion in
deionized water or seawater ajLO , 25*% and 8Q&C for 451 hr was examined. The per-
cent weight gain at 0® and 25^C was low (0.06^0 0.17 percent) and there was no
significant change in the flexural properties for these environmental conditions.
<^~~ At 80^p there was a decrease in the flexural strength of 17 and 20 percent in
seawater and deionized water, respectively. This is a comparison to control samples
exposed to 80°C heat alone. These decreases were found to be nearly reversible once
the samples Were dried. Optical microscopy did not reveal cracking of the matrix.
The flexural modulus was essentially unaffected by exposure to deionized water and
seawater at
* This research was sponsored by the MSFC 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 System").
Authors: B . C . Penn, J. G. Daniels,** F. E. Ledbetter, III,** M. L. Semmel,**
E . G . Goldberg,** W. T. White,** and J. M. demons**
** Materials and Processes Laboratory.
17. KEY WORDS
Composite Materials, Environmental Effects,
Glass/Epoxy, Seawater, Deionized Water,
Flexural Strength, Flexural Modulus
19. SECURITY CLASSIF. (of thU report)
Unclassified
18. DISTRIBUTION STATEMENT
Unlimited- -Unclassified
20. SECURITY CLASSIF. (of thli page) 21. NO. C
Unclassified 1
)F PAGES 22. PRICE
I NTIS
MSFC - form 3392 (M«y 1969)
For sale by National Technical Information Service, Springfield, Vurgtaia 22151
TABLE OF CONTENTS
Page
INTRODUCTION 1
EXPERIMENTAL PROCEDURE 1
RESULTS AND DISCUSSION 2
CONCLUSION 3
REFERENCES 5
LIST OF TABLES
Table
1.
2.
Title
Composition of Seawater Salt Mixture According to
Manufacturer ,
Percent Weight Gain for Glass /Epoxy Samples After Immersion
in Seawater and Deionized Water for 451 Hours
Page
6
6
3. Effects of Immersion in Deionized Water and Seawater at Various
Temperatures for 451 Hours on the Flexural Modulus and
Strength
TO-CEDING PAGE BLANK NOT
.JHTINTIONAI1Y BLANK in
TECHNICAL MEMORANDUM
EFFECTS OF SEAWATER AND DEIONIZED WATER AT 0 TO 80°C
ON THE FLEXURAL PROPERTIES OF A
GLASS/EPOXY COMPOSITE
INTRODUCTION
Composite materials are widely used in applications requiring high strength,
high stiffness, and low weight such as usage in automobiles and aircrafts. In order
to take full advantage of these excellent properties, the effects of service environ-
ments such as heat, temperature, and moisture on the mechanical properties of com-
posite materials need to be determined.
The effects of temperature and moisture on the mechanical properties of epoxy
resins reinforced with graphite [1-7] or glass fibers [8-11] have been studied.
Degradation of properties is believed to occur by moisture-induced plasticization or
moisture-induced cracking of the epoxy matrix [7-8]. Moreover, degradation of glass
fiber reinforced composites may occur by leaching of constituents from the reinforce-
ment fibers [ 8 ] •
The purpose of this paper is to present the results of a study concerned with
determining the effects of seawater versus deionized water on the properties of a
glass/epoxy composite.
EXPERIMENTAL PROCEDURE
Materials
Stratoglas glass/epoxy rod (1/4-in. diameter) was obtained from Air Logistic
Corporation, Pasadena, California. This composite, which consists of S-glass and a
proprietary epoxy resin, is prepared by a continuous molding process. The curing
agent is an amine.
The dry seawater salt mixture was purchased from Lake Products Co., St.
Louis, Missouri. The composition of this mixture is shown in Table 1. The seawater
solution was prepared by dissolving 41.95 g of the salt mixture in 1000 mL of water
as specified by the supplier.
Environmental Testing
Five-inch lengths of glass/epoxy rods were immersed in seawater at 0°C, 25°C
(room temperature), and 80°C for 451 hr. Control samples were prepared by sub-
jecting specimens to 80°C in a dry environment and to storage in a dessicator at room
temperature. After environmental exposure, the samples were subjected to micro-
scopic examination, percent weight gain determination, and flexural strength and
modulus measurements.
Percent Weight Gain Determination
The percent weight gain values presented in Table 2 are the average of two
5-in. length samples of glass/epoxy rod. The weight measurements were made using
a Mettler AE 160 analytical balance which has a readability of 0.1 mg.
Microscopic Examination
Environmental exposed and control samples were examined for cracks using a
Nikon SMZ-100 stereomicroscope at a magnification of 35X.
Fiber Content
The weight percent of fibers was 70 to 77 percent according to the manufac-
turer.
Flexural Testing
Testing was carried out in accordance with ASTM-D790 using the four-point
bend geometry. The length of the glass/epoxy rod samples was 5 in. The support
span and load span were 2 and 0.67 in., respectively. The tests were carried out
using an Instron testing machine at a rate of 0.1 in./min. Five samples were used
in determining environmental effects on the controls and current specimens (samples
tested immediately after removal from the environment). Four samples were used in
determining the flexural properties of residual specimens (samples that were dried to
constant weight after environmental exposure and then tested).
RESULTS AND DISCUSSION
Percent Weight Gains in Seawater and Deionized Water
The percent weight gains of samples immersed in seawater or deionized water
for 451 hr at 0°, 25°, and 80°C are summarized in Table 2. The range of values
obtained at 0° and 25°C are low (0.06 to 0.17 percent) and there is no significant
difference in the effect of seawater versus deionized water for these environmental
conditions.
At 80°C there was a significant increase in the percent weight gains of samples
exposed to seawater and deionized water compared to values obtained at 0° and 25°C.
The value obtained after immersion in seawater (1.2 percent) is not considered to be
significantly different than the percent weight gain measured after immersion in
deionized water (1.3 percent).
A white coating was observed on the samples immersed in seawater at 80°C
which could affect the long-term percent weight gain of the glass/epoxy composite.
This is based on work by Mazor et al. [12] who immersed graphite/epoxy composites
in seawater and deionized water for 11 years. These investigators found that samples
immersed in deionized water had the highest percent weight gain. The explanation
given for this result was that a thin coating formed on the surface of samples
immersed in seawater and acted as a barrier to absorption. In the present work the
samples were only partially covered; however, during long-term environmental
exposure, a more complete coating may form thereby decreasing the weight gains for
samples exposed to seawater.
Environmental Effects on the Flexural Properties
The effects of immersion in seawater and deionized water for 451 hr at 0°, 25°,
and 80°C on the flexural moduli and strengths are summarized in Table 3. The
flexural moduli values for deionized water and seawater at 0° and 25°C ranged from
5.99 to 6.21 Msi which is not significantly different than the value obtained for the
control (5.99 Msi). Moreover, the range of values (128 to 133 Ksi) obtained for the
flexural strengths did not vary significantly from the value of 132 Ksi measured for
the control sample. These results are not surprising because of the low percent
weight gain values of 0.06 to 0.17 percent found under these conditions. In addi-
tion, visual and optical microscopic examination did not reveal cracks.
At 80°C there was a significant decrease in flexural strengths of samples after
immersion in seawater and deionized water; however, the flexural modulus did not
change significantly. For example, compared to samples exposed to 80°C heat alone,
there was a decrease of 17 percent for samples immersed in seawater versus a value
of 20 percent for the samples immersed in deionized water. These decreases were
nearly reversed once the samples were dried. For example, samples immersed in
seawater or deionized and dried had only a 5 percent decrease in flexural strength
compared to the control which was heated to 80°C in an inert environment. This is
not considered to be significant since the standard deviations for the test samples were
1.5 to 3.4 percent. For this same reason, the difference in the flexural strengths
of seawater versus deionized water immersed samples at 80°C is not considered to be
significant.
The decreases in the flexural strengths of samples immersed in seawater or
deionized water for 451 hr at 80°C are most likely due to plasticization of the matrix
material as indicated by the 1.2 and 1.3 percent weight gains obtained under these
conditions (Table 2). Optical microscopy did not show moisture-induced cracking
under these environmental conditions. In addition, there was not a significant amount
of material leached out of the immersed samples based on their dry weight after
environmental exposure.
CONCLUSION
In this study, glass/epoxy samples were immersed in seawater and deionized
water at 0°, 25°, and 80°C for 451 hr. There was no significant difference in the
effect on the flexural properties of immersion in seawater versus deionized water for
the composite system used in this study.
At 0° and 25°C there was no significant difference in the flexural properties of
the immersed samples (deionized water and seawater) compared to the control samples
which were stored at 25°C in a dry environment. This is most likely due to the small
amount of water absorbed by the test specimens under these conditions. For
example, the percent weight gains were 0.06 to 0.17 percent.
There was a decrease of 17 percent in the flexural strength of samples immersed
in seawater at 80°C and 20 percent for those immersed in deionized water; however,
the change in the flexural modulus was not significant based on a comparison of
immersed samples and control samples exposed to 80°C heat in a dry environment.
The significant decreases in the tensile strengths of the immersed samples are most
likely due to moisture-induced plasticization based on percent weight gains of 1.2
and 1.3 percent for the seawater and deionized exposed samples, respectively.
REFERENCES
1. Browning, C. E., Husman, G. E., and Whitney, J. M.: Moisture Effects in
Epoxy Matrix Composites. 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. Tech-
nomic 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. 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. Ishai, O.: Polym. Eng. Sci., Vol. 15, No. 7, 1975, pp. 486 and 491.
9. Ashbee, K. H. G., and Wyatt, R. C.: Proc. Roy. Soc. A, Vol. 317, 1969,
p. 553.
10. Dewimille, B., and Bunsell, A. R.: Composites, Vol. 14, No. 1, 1983, p. 35.
11. Antoon, M. K., and Koenig, J. L.: J. Macromol. Sci.-Rev. Macromol. Chem.,
Vol. C19, No. 1, 1980, p. 135.
12. Mazor, A., Broutman, L. J., and Eckstein, B. H.: Polym. Eng. Sci., Vol.
18, No. 5, 1978, p. 341.
TABLE 1. COMPOSITION OF SEAWATER SALT MIXTURE
ACCORDING TO MANUFACTURER
Component Percent Composition
NaCl 59.490
MgCl2 26.460
Na2SO4 9.750
CaCl2 2.765
KC1 1.645
NaHCO2 0.447
KBr 0.238
0.071
SrCl2 0.095
NaF 0.007
TABLE 2. PERCENT WEIGHT GAIN FOR GLASS/EPOXY SAMPLES
AFTER IMMERSION IN SEAWATER AND DEIONIZED
WATER FOR 451 HOURS
Percent Weight Gain
Temperature (°C) Deionized Water Seawater
0 0.09 °-06
25 0.13 °'17
1 9fl
80 1.30 L'™
TABLE 3. EFFECTS OF IMMERSION IN DEIONIZED WATER AND SEAWATER
AT VARIOUS TEMPERATURES FOR 451 HOURS ON THE FLEXURAL
MODULUS AND STRENGTH (Values for the controls at 25°C
were 5.99 Msi and 132 Ksi and at 80°C they were
6.02 Msi and 135 Ksi, respectively.)
Flexural Modulus (Msi) Flexural Strength (Ksi)
Temperature (°C) Deionized Water Seawater Deionized Water Seawater
0 6.21 6.21 134 133
25 6.13 5.99 128 133
80
a. Current 5.99 6.28 108 112
b. Residual 6.02 5.79 129 128
APPROVAL
EFFECTS OF SEAWATER AND DEIONIZED WATER AT
0 TO 80°C ON THE FLEXURAL PROPERTIES
OF A GLASS/EPOXY COMPOSITE
(Center Director's Discretionary Fund Final Report)
By B. G. Penn, J. G. Daniels, F. E. Ledbetter, III , M. L. Semmel,
E . G . Goldberg, W. T. White, 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 work, in
its entirety, has been determined to be unclassified.
A. J. DEALER
Director, Space Science Laboratory
if U.S. GOVERNMENT PRINTING OFFICE 1986-631-058/20110


Effects of seawater and deionized water at 0 to 80 deg C on the flexural properties of a glass/epoxy composite

Effects of seawater and deionized water at 0 to 80 deg C on the flexural properties of a glass/epoxy composite

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