Effect of ply thickness and fibre orientation on delamination initiation in broken ply composite laminates

The present study examines the delamination initiation at the interface of broken and continuous plies in case of GR/E and GL/E laminates with broken central plies. A full 3D FE analysis has been performed with each layer of the laminate modelled as homogenous and orthotropic. The interface between the broken and continuous plies has been modelled with a thin resin rich la yer. Eight-noded isoparametric layered elements have been used to model the laminate specimen. Also, 3D contact elements are used to prevent the inter penetration of delaminated faces at the interface. Based on the results of 3D FE analysis, G(I), G(II) and G(III) have been calculated at the delamina tion front using Irwin's Crack Closer Integral. It has been observed that t he delamination initiation is a mixed mode phenomenon even in the case of u niaxial loading. Brewer and Lagace's Quadratic Stress Criterion has been us ed in conjunction with Linear Elastic Fracture Mechanics (LEFM) to calculat e the delamination initiation strain and the critical strain energy release rate (G(c)). The effects of various factors such as ply thickness, fiber o rientation, resin stiffness on G(c) have been studied for GR/E and GL/E lam inates having broken central plies.