Convergence of strain energy release rate components for Edge-Delaminated composite laminates

Abstract

Strain energy release rates for edge-delaminated composite laminates were obtained using quasi three-dimensional finite element analysis. The problem of edge-delamination at the −35 90 interfaces of an eight ply [0/±35/90] s composite laminate subjected to uniform axial strain was studied. A quasi three-dimensional finite element analysis was used to calculate the total and individual components of the strain energy release rate. The individual components did not show convergence as the delamination tip elements were made smaller. In contrast, the total strain energy release rate, G, converged and remained unchanged as the delamination tip elements were made smaller and agreed with the total G calculated using a closed-form equation derived from the rule of mixtures and classical laminated plate theory. The studies of the near-field solutions for a delamination at an interface between two dissimilar isotropic or orthotropic plates showed that the imaginary part of the singularity is the cause of the nonconvergent behavior of the individual components. To evaluate the accuracy of the results, an eight ply [0/±35/r/90] s laminate with the delamination modeled in a thin resin layer, similar to the resin layer that exists between the −35 and 90 plies, was analysed. Because the delamination exists in a homogeneous isotropic material, the oscillatory component of the singularity vanishes. The strain energy release rates remained unchanged as the delamination tip elements were made smaller. Comparison of the strain energy release rates for the ‘bare’ interface laminate, i.e. one without the resin layer, and for the laminate with the resin showed that the ‘bare’ interface models are a very good approximation for the resin case if the delamination tip elements were one-quarter to one-half of the ply thickness.