Multilayer hybrid-stress finite element analysis of composite laminate with through-thickness cracks

An assumed hybrid-stress finite element model using a simple composite multilayer element is developed to analyze generally thin or moderately thick composite laminates with through-thickness cracks. The assumed stress field satisfies: (i) equilibrium conditions within each layer, (ii) the traction reciprocity conditions at interlaminar boundaries, and (iii) the traction-free boundary conditions at the top and bottom faces of the laminate. Since the number of nodes and assumed stress parameters are independent of the number of layers, the multilayer element devised is quite effective especially for the laminate with a large number of layers. Several selected composite laminates with a through-thickness edge crack are solved. Many fewer degrees of freedom and only a one-step solution are necessary for the present technique. The variations of mixed-mode stress intensity factors across the thickness of the composite laminate are also computed. Excellent agreements between the present results and referenced solutions are drawn. The technique developed is also applicable to analyze the structural behaviors of the cracked laminate with arbitrary fiber orientation and stacking sequence for which the stress singularity has not yet been found.