Effects of Material Nonlinearity on the Three-Dimensional Stress State of Pin-Loaded Composite Laminates

Abstract

A three-dimensional nonlinear finite element code is established to analyze the effects of material nonlinearity on the state of stress and failure prediction near the stress concentrations of a pin-loaded laminated composite plate. Theoretically, stress singularities may occur at the interface between two layers of different ply orientation on the free edges. High magnitudes of stresses at the free edge of the ply interface are responsible for failure initiation at those locations. Therefore the state of stress near the edge of the hole and at the ply interface between two different layers is important and has been studied in detail. An existing nonlinear material model, for in-plane behaviour, has been modified to be applicable for three-dimensional cases. Nonlinear shear stress-strain behaviour of a unidirectional ply, in the x-y and z-x planes, is the source of nonlinearity. Three different configurations, namely, cross-ply [04/904] s, and [904/04] s and an angle-ply [+454/-454] s, were considered. A failure analysis, using stress based failure criteria, is performed to predict the failure initiation load of different configurations. The effect of material nonlinearity on the predicted failure initiation load is studied. The results of prediction of failure initiation load by considering the material nonlinearity is in excellent agreement with experimental results. The results obtained from failure analysis emphasize that considering the material nonlinearity, especially for highly shear induced cases like [+454/−454] s is important in failure analysis of composite laminates using stress based failure criteria.