Long-Term Moisture Absorption in Graphite/Epoxy Angle-Ply Laminates

Angle-ply laminates of graphite/epoxy Fiberite T300/1034, Ciba-Geigy T300/920 and Ciba-Geigy T300/914 were exposed to moist air of different relative humidities for 400 days. Laminates of T300/1034 reach a first plateau after about 100 days and a se cond plateau of saturation after about 400 days. The plateau levels are functions of the relative humidity and also of the residual stresses in the laminate. Compressive residual stresses retard the diffusion and lower the plateau levels. Laminates of T300/920 and T300/914 show more rapid moisture absorption than laminates of T300/1034 but no clearly detectable saturation plateau. The shoulder of the moisture content vs. square root of time curve is over-estimated by the one-dimensional solution of Fick's equation of moisture diffusion. A three-dimensional solution is given and is shown to predict the moisture absorption better for specimens of small width to thickness ratio.