Numerical study of the mixed-mode behavior of generally-shaped composite interfaces

The use of high-performance laminated composites and adhesively bonded structures has become very common for many engineering applications. Laminated structures are known to suffer from the non-linear and irreversible delamination process, including the formation and propagation of cracks, up to the complete detachment of the adhering parts. In this context, a new numerical formulation based on the generalized differential quadrature (GDQ) approach, is developed to determine the peeling and shear stresses along interfaces of arbitrary shape, made of laminated composite structures and subjected to mixed-mode conditions, as well as to examine the internal distribution of reactions and the kinematic response of the adherends. In line with a Linear Elastic-Brittle Interface Model (LEBIM), the specimen is considered as an assemblage of two sublaminates, partly bonded together by an elastic interface. This is, in turn, modeled as a continuous distribution of elastic-brittle springs acting along the normal and/or tangential direction, depending on the selected mixed-mode condition. A large parametric study is performed to predict the effect of the geometrical shape and curvature of the specimen on its structural response. The feasibility of the proposed formulation is also verified through a convergence analysis, for the simplest case of straight composite adherends, for which we provide a closed form analytical solution. The excellent agreement between the GDQ approach and the analytical predictions, confirms the reliable accuracy of the novel numerical formulation for the treatment of the mixed-mode fracture of composite materials or laminated joints of general shapes, as useful for practical strengthening requirements.