Study of the Influence of Inclusions on the Behavior of NiTi Shape-Memory Alloys in Thermal Cycling by Means of Finite Element Method

Despite the number of articles on the subject, the influence of inclusions on the behavior of nickel titanium shape memory alloys is still controversial. Numerical simulation can play a fundamental role in providing insight into this subject. As far as superelastic materials are concerned, it has been shown by means of finite element simulations that, in wires loaded in rotary bending conditions, the presence of inclusions greatly increases the stress distribution in the cross section, and that the maximum stress increases as the distance between the inclusion and the neutral axis increases. In this work, a similar approach is used to analyze the effect of inclusions on thermal cycles of wires loaded in tension. By means of a thermomechanical constitutive model implemented in ANSYS, the alternate stress/strain field in the presence of a particle is computed. The particle is either located close to the wire surface or in the center of the wire section. An empirical damage evolution law is applied to the stress strain field showing a region adjacent to the particle where premature mesocrack nucleation is likely to take place.