EFFECT OF STRETCHING-SHEARING COUPLING ON INSTABILITY-RELATED DELAMINATION GROWTH

Results are presented from a combined theoretical and experimental inv estigation into the effect of stretching-shearing coupling on the buck ling and growth of near-surface delaminated regions. Honeycomb sandwic h laminates with graphite/epoxy face sheets containing preimplanted, t hrough-width delaminations were tested in compression. Two layups were tested. Each layup contained delaminated regions with identical in-pl ane and flexural moduli; however, one layup exhibited stretching-shear ing coupling, whereas the other did not. Delamination buckling was pre dicted using a cylindrical buckling analysis, and energy release rates and fracture mode ratios were obtained by a crack tip element analysi s. Delamination growth was predicted using a linear, mixed-mode delami nation growth law. Significantly different delamination buckling and g rowth strains were predicted for the two layups. Predicted delaminatio n buckling and growth strains correlated well with experimental result s.