Experimental investigation on compressive behaviour of different patch-parent layup configurations for repaired carbon/epoxy composites

This work presents a comparison of various combinations of patch and parent laminates with different orientations and stacking sequence, on the performance of adhesively bonded external patch-repaired carbon/epoxy laminates under quasi-static compressive loading. The compressive behaviour and failure modes of pristine, damaged and repaired specimens of four different parent laminates ([0](6), [45](6), [0/45/45](s), [45/45/0](s)) are discussed. The repair of each parent laminate is carried out by bonding patches of four configurations ([0](2), [45](2), [45/0], [0/45]) having two plies on each side of the parent laminates. Real-time digital image correlation technique was employed to capture the development of the strain field with the increasing load. The results reveal the development of distinctive strain contours associated with different patch-parent configurations. The inspection of damaged specimens revealed the fiber micro-buckling as the dominant mode of failure. The orientation of plies influences the overall failure mode of the laminates. The clustering of 0 degrees plies results in laminate possessing higher strength. The less stiff [45](2) patch shows higher compliance with the increasing load.