Elastic–Plastic material response at noches and fatigue cracks by a coherent optics method

Elastic–Plastic material response near notch roots and fatigue cracks has been studied by moire interferometry, which is a coherent optics technique for high sensitivity full–field in–plane displacement measurement. Different materials, namley a NiCrMov steel, an as–cast aluminium alloy and precipitation–strengthened aluminium alloy, were studied. The evolution of residual deformations at blunt and sharp notches under monotomic loading conditions was determined. Non–linear finite–element companion calculations were performed for correlation purposes. Inhomogeneous plastic response, apparently due to the material microstructure, was observed and discussed. The presence of cyclic plastic zone at a fatigue crack tip, as well the localized strain distributions, have been investigated. Experimentally determined stress–intensity factors have been found to differ from linear elastic fracture mechanics predictions.