MOISTURE EFFECTS ON THE BEHAVIOR OF GRAPHITE POLYIMIDE COMPOSITES/

The effect of moisture on the material behavior of Magnamite(R) IM7 Gr aphite/Avimid(R) K3B thermoplastic polyimide composite laminates has b een investigated. Laminates consisting of a 62 vol% fiber were laid up with several different stacking sequences; [90](10) or unidirectional , [O-2/90](s) or thin cross-ply, [O-2/90(2)/O-2](s) or thick cross-ply , [45/O/-45/90](s) or quasi-isotropic, and [O/90] laminates. In this s tudy, the glass-transition temperature, T-g, and the intralaminar frac ture toughness, G(1c), were measured for dry and moisture-saturated un idirectional samples, When laminates were saturated with moisture, the value of T-g was found to decrease from its baseline (dry) value, but recovered upon redrying the samples. This observation is consistent w ith the effects of moisture on the T-g of other polymer composites. Pe rmanent toughness losses have not been observed in samples conditioned in room-temperature 75% and 100% relative humidity environments. Howe ver, during long-term conditioning of cross-ply and quasi-isotropic sa mples in liquid water, transverse cracks initiated in the absence of a n applied mechanical load. Moisture uptake curves for conditioning in room-temperature liquid water, 80 degrees C [176 degrees F] liquid wat er, and at room temperature and 75% relative humidity were used to cal culate Henry's Law constants and diffusion coefficients. Non-Fickian b ehavior, consisting of a postsaturation increase in moisture uptake, w as observed in cross; ply and quasi-isotropic laminates and might be d ue to the observed transverse cracking.