An environmental stress corrosion limit can be postulated from the results of a fracture mechanics study of an E-glass fibre composite fabricated from an isophthalic polyester resin. Both the rates of nucleation and crack growth indicated a diffusion controlled fracture mechanics mechanism. The fracture processes in the resin have been quantified using compact tension specimens. The effect of moisture on the values of K1ci and K1ca for crack initiation and arrest for the completely dried resin has demonstrated how the crack blunting processes occur. The moisture diffusion into the resin is characterised by a two-phase microstructure, which has been confirmed by scanning acoustic microscopy. A mechanism which involves a non-uniform stress distribution between the phases, has been developed. The proposed hypothesis may also explain the mechanism of microcavitation required for the transport of acidic environments through stressed resins as reported by Caddock et al. (7).
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