Hydrothermal Aging of Composite Materials Part 1 : Interfacial Aspects

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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 λb 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 λb or reduced aging time t/τ where τ is the relaxation time for hydrothermal degradation. The temperature dependence of λb is also shown to be modified by hydrothermal aging indicating possible changes in the chemical structure and rheology of the cured epoxy matrix phase.