The effect of delamination geometry on the compressive failure of composite laminates

One of the causes of a reduction in the compressive strength of a composite material containing delaminations is the buckling of the delaminated plies. To understand the effect of delamination geometry on the compressive behaviour of laminated composite materials, compression tests were carried out on glass-fibre-reinforced plastic (GRP) test specimens containing artificial delaminations of various geometry, created by inserting PTFE film into the laminate during lay-up. Finite-element modelling was also carried out to gain further understanding of the mechanisms of compressive failure. Good agreement between finite-element predictions and experimental measurements were found for the whole range of delamination geometries that were tested. Finite-element and simple closed-form models were also developed for delaminated panels with isotropic properties. This enabled a study of the effect of delamination geometry on compressive failure without the complicating effects of orthotropic material properties. The results of this study can be used to derive a graph of non-dimensional failure load versus non-dimensional failure stress, where the results for any one delamination geometry superimpose on those for all others.