Model to accurately predict out-of-plane shear stiffness reduction in general cracked laminates

Abstract The practically important problem of the modification of laminate out-of-plane shear stiffness by ply cracks is hardly investigated in the literature. In this paper, out-of-plane shear stiffness reduction of laminates containing uniform and non-uniform distributions of ply cracks is studied. A novel variational model is developed to determine accurately stress transfer mechanisms and consequently out-of-plane shear stiffness reduction of general cracked laminates under applied out-of-plane shear loads. It is shown that the presence of ply cracks in a laminate under out-of-plane shear loads, perturbs the uniform distribution of shear stresses and induces high gradients of in-plane stresses leading to large shear stiffness reductions. The results are compared with those of the finite element method (FEM) implementing periodic boundary conditions. It is shown that there is excellent accordance between the results obtained from these approaches. The outcome of the paper provides necessary information for determination of damage-based constitutive laws for composites.