Controlled energy dissipation in fibrous composites. II: Microscopic failure mechanisms

Mechanical properties and microscopic fracture mechanisms of continuous fiber reinforced polymer composites were investigated. Perforated polyimide films (e.g. Kapton®) were added between composite prepreg layers to modify the interlaminar bonding strength. Addition of highly perforated films can increase the toughness of unidirectional glass/epoxy composites without an appreciable reduction in strength. The fibrous composites studied exhibit two fracture modes (compressive and tensile) when failed by three‐point bending. In general, the compressive failure mode preceded the tensile failure mode. Real‐time acoustic emission (AE) analysis was found to provide more fracture information which is otherwise not discernible from mechanical testing alone. The crack initiation stress level and the subsequent crack propagation mode were identified by real‐time AE during deformation and by post‐failure scanning electron microscopy fracture surface analysis.