Using acoustic emission to assess shear strength degradation in FRP composites due to constant and variable amplitude fatigue loading

Acoustic emission was used to assess static shear strength degradation, due to fatigue, in unidirectional fibre-reinforced composites. According to standard specifications, [±45]S specimens were used. Coupons, made of Gl/Ep material, were subjected to tensile constant or variable amplitude loading, at several stress level and life fraction combinations, to investigate influence of various loading configurations on damage accumulation. Two acoustic emission descriptors were introduced and respective engineering models, estimating residual strength, were developed. The performance of the former scheme was excellent, although knowledge of the maximum loading stress value was required in the implementation. In the second scheme, on the other hand, no additional information on the specimen load history was needed. The potential of both models was also validated on two independent verification sets: one consisting of specimens loaded under a variable amplitude spectrum and another of an alternative matrix system, subjected to constant amplitude fatigue.