Numerical modeling of the debonding process of mixed-mode composite double cantilever beams

Nowadays, several engineering components are made of high performance laminated composites and adhesively bonded interfaces. One of the most serious damage modes of laminated structures is related to the non-linear and irreversible delamination process, including the formation and propagation of inter-laminar cracks, up to the complete detachment of the adhering parts. This work focuses on the development of a new numerical formulation to determine the debonding onset and propagation along weak interfaces under different mixed-mode conditions. The interfacial problem is addressed by means of the cohesive crack modeling, concentrating all non-linearities at the interface. This means that interfaces are considered as an assemblage of two sublaminates, partly bonded together by an elastic interface, here modelled as a continuous distribution of elastic springs acting along the normal and/or tangential direction, depending on the interfacial mixed-mode condition. This generalizes the idea suggested recently in [1] for a single mode-I debonding, which is here extended to include mixed loading, geometrical and mechanical conditions. The numerical predictions in terms of crack advancement, length of the process zone, maximum load and load-deflection response, are compared to the main results based on a frictional contact formulation. This is here generalized to handle cohesive forces along the normal and tangential directions, as employed in [2-4]. The very good agreement between the proposed numerical approach and a combined contact- debonding algorithm, confirms the feasibility and accuracy of the proposed formulation when studying delamination phenomena occurring within composite materials or laminated joints, usually subjected to mixed-mode conditions.