Moisture Effects in Epoxy Matrix Composites

The effect of absorbed moisture on the mechanical properties of a neat epoxy resin and derived graphite/epoxy composites is investigated. Glass transition temperature and modulus as a function of mositure content and temperature are determined for both the neat resin and composite. In addition, elastic modulus for the neat resin and strength and elastic moduli for unidirectional composites and quasiisotropic laminates are determined as a function of absorbed moisture and temperature. A method for predicting moisture content and through-the-thickness profile for a laminate exposed to a constant humidity and temperature is discussed. Particular attention is given also to the details of environmental testing.

Data indicate that absorbed moisture and temperature effects on the neat resin translate directly to matrix dominated properties of the composite and can lead to a change in failure mode, while filament dominated properties show very little environmental sensitivity. Results also indicate that resin glass transition temperature is a function of processing as well as absorbed moisture.