Effect of in-plane residual stresses on the post-deflection behaviour of a T-shaped deflected crack in layered systems

Post-deflection behaviour of a T-shaped crack in a bilayer material system under the presence of in-plane residual stress was investigated for a four-point bending configuration. Non-dimensional parameters for generalization of the residual stress state in a bilayer system were defined using globally measurable quantities such as curvatures and axial strains. It was predicted that the residual stress varying from tension at the outer edge to compression at the interface was beneficial to prevent kinking of the T-shaped crack out of the interface and therefore to toughening of the layered composites. However, it was expected that appreciable improvement in toughness properties was possible only when the intact layer is stiffer than the cracked layer. Further, incorporation of residual stresses higher than a certain level did not result in a further improvement in the toughness properties. Criteria for crack deflection-induced toughening of layered composites were derived from these predictions.