This study investigates the effect of exposure to elevated temperatures on the mechanical properties and moisture absorption kinetics of a graphite/epoxy composite laminate. 16-ply unidirectional AS4/3501-6 laminates are cured in an autoclave. The temperature profile during cure cycle involves a ramp of 5°C/min followed by a 3-hour hold at 177°C (350°F). The test samples obtained from these laminates are subjected to 150, 200, 250, 275, 300 and 325°C for 30min. Flexural strength and stiffness of the samples are characterized by three-point bending tests before and after the temperature exposure. These samples are then immersed into distilled water at 80°C and weighed at regular intervals to characterize their moisture absorption kinetics. Stiffness remained nearly unaffected from exposure to elevated temperatures except for 300 and 325°C. At 300 and 325°C, up to 21% and 58% reductions in flexural stiffness with respect to the control samples is observed, respectively. On the other hand, flexural strength displayed slight reduction at 250°C and resulted in over 60% and 88% deterioration for 300 and 325°C, respectively. Exposure to 150 and 200°C did not result in significant changes in mechanical properties. However, moisture absorption experiments indicated an increase in the rate of diffusion even if the mechanical properties are unaffected. The diffusion coefficient displayed an increase of 27% for 150°C, 75% for 200°C, reaching a maximum increase of 600% for 300°C exposure.

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