Delamination Initiation at the Interface of Broken & Continuous Plies In FRP Composite Laminates

Abstract

Delamination is a very common and the weakest mode of failure in laminated composite structures. Two common phenomena viz. free edges of laminates and broken plieslfibres usually give rise to delamination. Ply or fibre breakage in composite laminates usually occurs as a result of low velocity impact. Consequently, the interface between the broken and the continuous plies becomes the weakest link from the failure point of view of the laminate. It has been reported by the earlier researchers that delamination at the interface usually precedes the final fracture of such broken ply composite laminates . The present work has been aimed at evaluating the delamination initiation stress for unidirectional [0°] GL/E and GR/E laminates having one or more central plies broken. A 3D finite element analysis has been used to model the laminate ply by ply and the initial stress analysis results indicate that delamination will occur at the interface of the broken and the continuous plies which agree with the already published results . Also. the concept of LEFM (Linear Elastic Fracture Mechanics) has been incorporated in the finite element analysis to evaluate the Energy Release Rate (G), at the delamination front to assess the delamination initiation. Effects of various important factors such as number of plies, thickness of the laminate and stiffness of the interfacial resin layer on the delamination initiation has been studied and interesting observations are made. It has been observed that thicker the specimen,lower is the delamination initiation stress for the specimen. Also, it has been concluded from the analysis that as the interfacial resin becomes stiffer, energy release rate at the delamination front decreases.