Numerical bond assessment of carbon-epoxy stepped-lap joints

With the main purpose of obtaining lightweight and durable structures, bonding techniques have improved significantly in several industries. Depending on the type of structure, joining different components with different materials may require different joint geometries, which may perform better or worse. Still, only the bond performance of a very limited number of joint geometries is well known. A lack of knowledge, for instance, about the debonding process of one and two-step joints persists, especially for the latter. The present work intends to mitigate this gap by studying the debonding processes of one and two-step joints made with CFRP and aluminium adherends. To that end, implicit and explicit numerical methods (finite and distinct element methods, respectively), were applied to study different joint geometries and identify which one shows the best bond performance when subjected to a monotonic load consistent with pure fracture mode II. Based on the bond stresses obtained within the interface of the joints, the debonding propagations of the one and two-step joints are analyzed thoroughly. In the case of the one-step bonded joints, the results revealed that when the ratio between the axial stiffness of the adherends is r = 1.0 the load capacity of these joint configurations is maximized. With two-step joints, the load capacity is very sensitive to the relationship between the axial stiffness on the left (ra) and right-hand side (rb). Based on 162 different numerical simulations, the results also suggest that the load capacities of the two-step joint configurations can be maximized when the axial stiffness ra and rb of the joint are equal to 1/3 and 3.0, respectively.