The Effect of Temperature and Moisture Content on the Flexural Response of Kevlar/Epoxy Laminates: Part I. [0/90] Filament Orientation*

Abstract

This study examines the effects of moisture and temperature on the flexural response of [0/90] Kevlar 49 fabric-reinforced epoxy laminates. Two high temperature (190°C) cure commercially available epoxies, Narmco 5208 and Ferro CE-9000, were used as matrix materials. Results indicate that the mechanical properties of Kevlar 49/epoxy laminates are temperature dependent over the range -55°C to 150°C. The addition of moisture magnifies temperature sensitivity. At 150°C and near saturation moisture content (5 weight percent), a strength loss of 60-70 percent and an effective stiffness loss of 40 percent from dry, room temperature values are measured. At 21°C, saturated specimens are found to be 35-40 per cent weaker than dry material. At low temperature (-55°C), strengths increase with the addition of moisture. Over the range of conditions tested, failure was not catastrophic, but was characterized by a loss in load carry ing capacity. Microscopic examination of failure modes indicates that flexural strength is determined by the ease with which filaments compres sively buckle. These results indicate that care must be taken when design ing with Kevlar-reinforced composites for use at elevated temperatures after exposure to moist environments. An accurate prediction of the ex pected composite moisture content and service temperature is important to the design process.

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References

J. Hertz , "Moisture Effects on the High-Temperature Strength of Fiber-Reinforced Resin Composites, " Proceedings of the 4th National SAMPE Technical Conference, Society for the Advancement of Material and Process Engineering, Azusa, CA, 1972, pp. 1-7.

H.L. Young and W.L. Greever , "High Temperature Strength Degradation of Composites During Aging in the Ambient Atmosphere," in Compoiste Materials in Engineering Design, B. R. Noton, Ed., American Society for Metals, Metals Park, OH, 1972 , pp. 695-715.

Environmental Effects on Advanced Composite Materials, ASTM STP 602, American Society for Testing and Materials, 1976.

Advanced Composite Materials — Environmental Effects, ASTM STP 658, American Society for Testing and Materials , 1978.

C.W. Browning , "The Mechanisms of Elevated Temperature Property Losses in High Performance Structural Epoxy Resin Matrix Materials after Exposures to High Humidity Environments," Polym. Engr. and Sci. 18, 1, January 1978, pp. 16-24.

R.J. Morgan and J.E. O'Neal , "The Durability of Epoxies," Polym-Plast. Techn. and Engr., 10 , 1, 1978, pp. 49-116.

C.E. Browning , G.E. Husman and J.M. Whitney , "Moisture Effects in Epoxy Resin Matrix Composites," Composite Materials: Testing and Design, ASTM STP 617, American Society for Testing and Materials, 1977, pp. 481-496.

L. Penn and F. Larsen , "Physicochemical Properties of Kevlar 49 Fiber," J. Appl. Poly. Sci., 23, 1, January 1979, pp. 59-74.

R.E. Allred and A.M. Lindrose , "The Room Temperature Moisture Kinetics of Kevlar 49 Fabric/Epoxy Laminates," Composite Materials: Testing and Design, ASTM STP 674, American Society for Testing and Materials, 1979, pp. 313-323.

10.

J.M. Augl , "Moisture Sorption and Diffusion in Kevlar 49 Aramid Fiber," Naval Surface Weapons Center Report NSWC/TR-79-51, Silver Spring, MD , March 1979.2

11.

W.S. Smith , "Environmental Effects on Aramid Composites," E. I. duPont de Nemours, Textile Fibers Dept. Report, Wilmington, DE, 1980.

12.

N.J. Abbott , J.G. Donovan , M.M. Schoppee , and J. Skelton , "Some Mechanical Properties of Kevlar and Other Heat Resistant, Nonflammable Fibers, Yarns, and Fabrics," Fabric Research Laboratories Report AFML-TR-74-65, Part III, Dedham, MA, March 1975.

13.

R.E. Trujillo and B.P. Engler , "Chemical Characterization of Composite Prepreg Resins. Part I." Sandia Laboratories Report SAND 78-1504, Albuquerque, NM, December 1978.2

14.

R. E. Trujillo and R. A. Assink, Sandia Laboratories, unpublished data.

15.

R.E. Allred and N.H. Hall , "Volume Fraction Determination of Kevlar 49/Epoxy Composites," Polym. Engr. and Sci., 19, 13, October, 1979, pp. 907-909.

16.

A. K. Miller, Sandia Laboratories, unpublished data.

17.

J.M. Whitney and G.E. Husman , "Use of the Flexure Test for Determining Environmental Behavior of Fibrous Composites," Expl. Mech ., 18, 5, May 1978, pp. 185-190.

18.

C. Zweben , W.S. Smith and M.W. Wardle , "Test Methods for Fiber Tensile Strength, Composite Flexural Modulus and Properties of Fabric-Reinforced Laminates," Composite Materials: Testing and Design, ASTM STP 674, American Society for Testing and Materials, 1979, pp. 228-262.

19.

C. Zweben , "The Flexural Strength of Aramid Fiber Composites," J. Comp. Mat'ls., 12, October 1978, pp. 422-430.

20.

C. Zweben and M.W. Wardle , "Flexural Fatigue of Marine Laminates Reinforced with Woven Rovings of E-Glass and of Kevlar 49 Aramid," Proceedings of 34th Annual Conference Reinforced Plastics/Composites Institute, Society of the Plastics Industry, New Orleans, LA, 1979, Section 4C, pp. 1-6.

21.

J.H. Greenwood and P.G. Rose , "Compressive Behavior of Kevlar 49 Fibres and Composites," J. Matl. Sci., 9, 1974, pp. 1809-1814.

22.

S.V. Kulkarni , J.S. Rice and B.W. Rosen , "An Investigation of the Compressive Strength of Kevlar 49/Epoxy Composites," Composites, September 1975, pp. 217-225.

23.

R.M. Jones , "Apparent Flexural Modulus and Strength of Multimodulus Materials," J. Compt. Mat'ls., 10, October 1976, pp. 342-351.

24.

"Kevlar 49 Data Manual," E. I. DuPont de Nemours, Wilmington, DE.

25.

"Flexural Properties of Plastics," ASTM Designation D 790-71 , American Society for Testing and Materials, Philadelphia, PA, 1978.

26.

R.J. Morgan , J.E. O'Neal and D.B. Miller , "The Structure, Modes of Deformation and Failure, and Mechanical Properties of Diaminodiphenyl Sulphone-cured Tetraglycidyl 4,4' Diaminodiphenyl Methane Epoxy," J. Matl. Sci., 14, 1, January 1979, 109-124.

27.

R.E. Allred , N.H. Hall and A.K. Miller , "Moisture and Post-Cure Effects on the Matrix Glass Transition Temperature of Kevlar/Epoxy Laminates," to be submitted to Polym. Engr. and Sci.

28.

Ciba-Geigy Corp., Ardlsey, NY, product data.