Failure mechanisms under compression loading in composites with designed out-of-plane fibre waviness

Compressive strength reduction due to fibre waviness is a key concern in composite structures. Specimens with fibre misalignments representative of those that can occur at ply drops and resin rich areas in components were manufactured by incorporating either two or 10 discontinuous plies oriented either in 0 degrees ('longitudinal') or 90 degrees ('transverse'). Longitudinal specimens did not fail in compression but failed by delamination initiating at the ply drops. Transverse specimens did not fail directly due to the waviness: specimens with 8 degrees waviness failed at similar stresses and strains as fully aligned specimens, while 30 degrees waviness specimens failed in the aligned plies at a slightly reduced overall stress due to redistribution of load from the less stiff wavy plies. None of the specimens failed directly in compression due to misalignment in the wavy plies, indicating that this is not necessarily the critical failure mechanism, and highlighting the importance of delamination and load redistribution at ply drops.