Experimental investigation and characterisation techniques of compressive fatigue failure of composites with fibre waviness at ply drops

Abstract

Internal features, such as fibre waviness and ply drops, have an impact on fatigue performance of composite structures. In this investigation, specimens were manufactured with wavy plies sandwiched between straight plies by placing blocks of discontinuous plies anti-symmetrically on either side of the continuous wavy plies. The specimens were representative of the kind of fibre misalignment that can occur in components at ply drops and resin rich areas. Experimental characterisation techniques using strain gauge software were also developed for detecting the initiation of delamination and its propagation, by measuring interlaminar transverse displacements. Specimens with longitudinal discontinuous plies did not fail in compression but rather failed by delamination initiating at the ply drops. None of specimens with transverse discontinuous plies failed directly in compression due to misalignment in the wavy plies. The fatigue failure mechanisms are the same as those observed under static loading in previous work, which facilitates development of a fatigue model.