Asymmetric shielding mechanisms in the mixed-mode fracture of a glass/epoxy interface

An asymmetric increase in the apparent values of the interfacial fracture toughness with increasing mode II component of loading has been observed by several investigators. In this study, cracks were grown in a steady-state manner along the glass/epoxy interface in sandwich specimens in order to determine the mechanisms responsible for the shielding effect. Finite element analysis using a hydrostatic stress and strain rate dependent plasticity model for the epoxy and a cohesive zone model for the interface shows that plastic dissipation in the epoxy accounts for the asymmetric shielding seen in these experiments which cover a wide range of mode mb. Numerical predictions of normal crack-opening displacements yielded results that were consistent with measured values which were made as close as 0.3 mu m from the crack tip.