Nonlinear mechanics of delamination in fiber-composite laminates: asymptotic solutions and computational results

A delamination in a composite laminate under mechanical loading involves an interface crack between dissimilar, anisotropic composite plies undergoing coupled I, II and III deformation modes. With the presence of high crack-tip local stresses, the effect of inherently nonlinear composite material constitutive properties on the delamination becomes an interest and important issue. In this paper, a nonlinear anisotropic laminate elasticity formulation is introduced to establish governing field equations for a delamination between dissimilar fiber-composite plies. In the context of nonlinear fracture mechanics, the dominant stress singularity and asymptotic solution structure are determined for a delamination in a composite laminate with nonlinear ply constitutive properties. A computational method is used to analyze the delamination field in a composite with complex lamination variables. Delamination energy release rates associated with individual modes are obtained for symmetric angle–ply composite laminates for illustration. Several case studies are conducted to compare the solutions for nonlinear delamination problems with those of corresponding linear interface-crack problems. Unique features of nonlinear composite delamination mechanics are presented, including the order of stress singularity, coupled tearing-mode contributions, and large delamination closure due to strong ply material anisotropy, discontinuity and Poisson’s effect.