Moisture absorption in graphite/epoxy laminates

This work investigates the uptake of moisture by XAS-914C and AS4/3501-6 graphite/epoxy composite laminates under a range of temperature and humidity conditions. From the experiments, the diffusion coefficients of moisture in a number of laminates have been determined, together with the equilibrium moisture levels in the matrix.

The effects of thermal spiking (thermal transients simulating supersonic heating of military aircraft) on moisture uptake were determined experimentally using a number of combinations of spiking and moisturising conditions. Thermal spiking was found to be damaging when moisture was present in the laminate, and spiking during moisturising was found to be more severe than thermal spiking of material conditioned to equilibrium moisture levels. The pronounced effects of repeated thermal spiking on moisture uptake suggest a progressive form of spiking damage, and a simple model is proposed of a damage zone progressing through the laminate during successive moisturising then spiking cycles.