Effect of stretching-shearing coupling on instability-related delamination growth

Results are presented from a combined theoretical and experimental investigation into the effect of stretching-shearing coupling on the buckling and growth of near-surface delaminated regions. Honeycomb sandwich laminates with graphite/epoxy face sheets containing preimplanted, through-width delaminations were tested in compression. Two layups were tested. Each layup contained delaminated regions with identical in-plane and flexural moduli; however, one layup exhibited stretching-shearing coupling, whereas the other did not. Delamination buckling was predicted using a cylindrical buckling analysis, and energy release rates and fracture mode ratios were obtained by a crack tip element analysis. Delamination growth was predicted using a linear, mixed-mode delamination growth law. Significantly different delamination buckling and growth strains were predicted for the two layups. Predicted delamination buckling and growth strains correlated well with experimental results.