An insight into the mechanical behavior and failure mechanism of CFRP/Al adhesively bonded structures subjected to low-velocity impact

Experimental and numerical methods are used to investigate the effects of different impact surfaces and energies on the mechanical properties and failure behavior of CFRP/Al adhesively bonded structures. To predict the damage initiation and propagation of CFRP laminates, inter laminar and adhesive layer, and aluminum alloy plates, the integrated finite element model containing both low-velocity impact (LVI) and axial tensile after impact (TAI) processes is developed by combining continuum damage mechanics model, cohesive zone model, and Johnson-Cook model. Additionally, LVI and TAI tests have been performed on the corresponding adhesively bonded structures with aluminum alloy 5182 (AA5182) and CFRP laminate as impact surfaces, which verify the effectiveness of the proposed integrated FEM. The results indicate that AA5182, as the impact surface, produces greater impact damage (maximum crater depth and opening width) in the center of the overlap region in comparison with the CFRP. The residual bearing capacity of the joints is the result of the competition between impact behavior and mechanical interlocking. The tensile strength, stiffness, and failure displacement of the joints decrease with the increase of impact energy. The failure modes of the joints include annular and circular cohesive failure of the adhesive layer in the impact region, interface failure, cohesive failure and peeling failure in the non-impact region, delamination damage, and fiber pullout and matrix cracking of the CFRP laminate. This investigation can provide good technical support for the structural design of heterogeneous material connections.