Jim Stian Olsen

Effect of Micro-voids on Plasticity in NiTi-alloys

Recent experimental investigations have indicated that commercial NiTi superelastic alloys consist of particles and inclusions which can nucleate micro-voids. Almost no study on the effect of micro-voids has been carried out in the literature. In this study the effect of micro-voids and plasticity on the behaviour of a superelastic NiTi-alloy has been investigated. Axisymmetric unit cell models with different micro-void volume fractions have been analysed subjected to various stress triaxiality states. It is shown that the onset of plasticity is located at the void edge as the maximum stress initially occurs at this position. The finite element results indicate that the existence of micro-voids can reduce the re-centring capabilities in NiTi-alloys and that this effect should be taken into consideration of constitutive equations.