Modeling laminates using a layerwise finite element with enhanced strains for interlaminar stress recovery and delamination characteristics

Abstract

A layerwise finite element with enhanced strains is developed for the analysis of laminates with special emphasis on the recovery of interlaminar stresses and the study of delamination characteristics. A laminate interface, where stresses are to be computed, is modeled as a contact zone between portions of the laminate separated by this interface. Interlaminar stresses are recovered at this interface from the equilibrium consideration. Effectiveness of this interface model is studied by solving for interlaminar stresses in a laminated composite plate in bending. The interlaminar stresses recovered from the present study are compared with exact solutions and those obtained with other stress recovery methods. Present method of stress recovery is further applied to a free edge problem wherein an angle-ply laminate in bending is considered, and the results are compared against that from the VKFE solutions of Robbins and Reddy. Characteristics of the interface model are studied for a delamination problem by considering a double cantilever problem under a splitting load. Since the interface model provides the facility for the closure of delamination by a small amount, strain energy release rates were evaluated by actual crack closure (Crack Closure Method) and by virtual crack closure (Virtual Crack Closure Method) for a comparative study. Finally, a cylindrical cross-ply laminate in bending is considered for its delamination characteristics. The critical load before delamination growth is studied for different initial geometries of the laminate differing in their delamination length and imperfection ratio values. Influence of the variation in strength parameters such as strain energy release rates on the critical load values has also been studied.