Hydrothermal Aging of Composite Materials Part 1 : Interfacial Aspects

Abstract

A surface energetics theory of bonded interfaces is applied to design graphite-epoxy composites with controlled moisture sensitivity at the fiber-matrix interface. Hydrothermal (100°C in H₂O), aging of the composite materials shows an equilibrium degree of degradation in interlaminar shear strength λ_b which is in reasonable agreement with theoretical expectation. Hydrothermal aging produces changes in composite acoustic response, both sound velocity C₂ and attenuation α₂, which correlate with changes in λ_b or reduced aging time t/τ where τ is the relaxation time for hydrothermal degradation. The temperature dependence of λ_b is also shown to be modified by hydrothermal aging indicating possible changes in the chemical structure and rheology of the cured epoxy matrix phase.