DELAMINATION FAILURE IN HYBRID COMPOSITES: THE EFFECT OF THE STACKING SEQUENCE.

The present work describes a study of the delamination fracture behavior of graphite/glass-epoxy hydrids containing surface cracks of various depths. The effect of changing the stacking sequence at constant volume fractions of symmetrically laminated hybrids was analysed by varying both the number and the order of the graphite and glass laminate across the material thickness. It was found that the tensile fracture strength of all the hybrids was notch-insensitive, probably because the Cook and Gordon crack tip deflection mechanism was active. Since delamination was the governing process for damage initiation, the delamination strength was measured experimentally. The dependence of the delamination strength on the lay-up sequence was regarded as a 'hybrid effect', the understanding of which would be critical in practical design problems. Hence, a theoretical model based on strain energy balance considerations was developed.