Determination of geometric role and damage assessment in hybrid fiber metal laminate (FML) joints based on acoustic emission

The ultimate damage patterns of bolted composite joints would change from bearing damage to shear damage due to different geometric parameters . However, it is still a challenging task to evaluate real-time damage progressive of hybrid (bolted/bonded) FML joints consisting of complex components in detail. Here, acoustic emission (AE) combined with a digital image correlation system (DIC), optical microscope and C-Scan technique is applied to describe the mechanical responses of hybrid FML joints under quasi-static uniaxial tension load with an emphasis on determining the geometric role of joint on the damage propagation . A k-means cluster algorithm as an unsupervised pattern recognition approach is used to classify each failure mode occurring in the joints to further establish the connection between experimental phenomena and underlying mechanisms. The damage modes including matrix cracking , debonding of adhesive layer , fiber breakage and metal fracture are identified by clusters of AE signals, distributions of strain field and damage morphology . The results clearly reveal the effect of varied geometric parameters on damage propagation of hybrid FML joints and provide a framework for analyzing the relationship between the failure modes in FML and related AE parameters.