Experimental study on failure mechanism of CFRP-to-aluminium single-lap adhesive joints under tension after out-of-plane pre-impact

This paper presents the influence of impact energy and impact surface on the impact damage characteristics and residual tensile performances of carbon fibre reinforced plastics (CFRP)-to-aluminium single-lap adhesive joints. Experimentally, the internal damage morphologies of joints after pre-impact were inspected with X-ray micro-computed tomography (X-CT). The failure processes and detailed fracture surfaces were obtained by the digital image correlation (DIC) system and scanning electron microscopy (SEM). The results show that the joints impacted on aluminium surfaces exhibit superior impact resistance to the CFRP pre-impact surface under the out-of-plane impact load. The joints pre-impacted on different surfaces have similar failure processes during the tensile process. Firstly, the delamination damage propagates from the impact location to the edge of overlap region. Subsequently, the delamination damage reaches the CFRP end, where the local stiffness of CFRP adherend is significantly reduced, and cracks appear in the adhesive layer. Finally, the cracks propagate from the CFRP end to the overlap area centre with further increased tensile load, and the joint rapid fracture occurs after the tensile load reaching its peak. The delamination damage of CFRP adherends caused by out-of-plane impact load is the dominant factor to affect the bearing capacity of CFRP-to-aluminium single-lap adhesive joints.