Experimental investigation into the effect of edge stitching on the strength and fatigue life of co-cured joints between cross-ply adherends,

An experimental study was conducted to investigate the effect of stitching on the static and fatigue response and related failure modes of co-cured single-lap joints between composite adherends. Two cross-ply layups, [0 2/90]s and [90/02]s, were selected for the adherends, with the aim of studying the influence of the layer orientation at the joining interface (0'I-0I for joints between [0 2/90]s adherends and 90'I-90'I for joints with [90/0 2]s adherends). It was found that stitching did not affect the static behaviour of [02/90]s joints, but it resulted in a 36% increase in the static strength of joints between [90/0 2]s adherends. However, stitching significantly improved the fatigue life of both [02/90]s and [90/0 2]s joints by extending the durations of both the crack nucleation and propagation stages. Direct observations indicated that the bridging action of stitches (which remained intact throughout the entire fatigue life of the joints) on delaminated adherends is the physical mechanism responsible for the extension of the crack propagation phase.