Demonstration of pseudo-ductility in unidirectional discontinuous carbon fibre/epoxy prepreg composites

The inherent brittleness of continuous unidirectional fibre reinforced composites is a major drawback to their otherwise outstanding mechanical performance. This paper exploits composites with overlapped discontinuities at the ply level to create a significantly non-linear response, due to progressive interlaminar damage under tensile loading. Two distinct configurations were manufactured with the same carbon/epoxy system and tested under quasi-static tension, showing that varying the thickness and length of the overlapping ply blocks resulted in significantly different mechanical responses and failure modes. A previously developed generalised shear-lag model was successfully used to optimise the overlap configuration, and accurately predicted the response in both strength- and toughness-dominated cases. This work demonstrates that unidirectional composites with well-designed discontinuities at the ply level can provide a significantly non-linear response with clear warning before failure, while retaining similar stiffness and up to 50% of the strength of their continuous counterparts.