UNDERSTANDING THE SEQUENCE OF DAMAGE IN COMPLEX HYBRID COMPOSITE-METALLIC STRUCTURES SUBJECT TO OUT-OF-PLANE LOADING INVESTIGATED USING COMPUTED TOMOGRAPHY

The progression of damage in a hybrid composite-metallic structure subject to out-of-plane loading has been examined throughout an interrupted quasi-static-indentation test using micro-focus computed tomography for damage assessment. Two key damage events were identified from the load-displacement tests. The CT data shows that the first damage mechanisms to occur are yielding of the aluminium substrate and matrix cracking in the CFRP; the onset of these damage mechanisms occurs at a similar point in the loading process. With increasing load, delamination occurred between all plies in the CFRP layer. The bonded interface between the aluminium and CFRP was maintained at lower loads - a crack initiated preferentially within the innermost CFRP ply rather than at the interface between the two materials. The CT data indicates that the second damage event on the load-displacement curve can be attributed to CFRP fibre fracture, consistent with contact forces. This work indicates that relatively low-level out-of-plane loads are likely to cause plastic deformation to the aluminium substrate, whilst the integrity of the fibre in the CFRP is maintained until higher loads.