Asymmetrical Bending Model for NiTi Shape Memory Wires: Numerical Simulations and Experimental Analysis

A detailed numerical and experimental study of a NiTi Shape Memory Alloy (SMA) wire subjected to bending is presented in order to provide a complete characterisation of the material under this load case. The beam model presented is based on the classic Euler-Bernoulli theory and uses De la Flor one-dimensional constitutive equations modified to take into account different material responses to tension and compression as well as the different elastic properties of austenite and martensite. All the necessary experimental techniques were designed to determine the bending behaviour of NiTi SMA wire over the entire range of transformation temperatures. These experimental bending results were then compared with the numerical results. The numerical model proposed agrees quantitatively and qualitatively with the experimental bending results obtained for NiTi wire, representing an effective tool for the analysis of one-dimensional structural devices. A comparison of the numerical results that assume symmetrical behaviour between tension and compression with the results that assume asymmetrical behaviour has shown that the tension/compression asymmetry is more pronounced in the martensitic range and has little influence on the response of the SMA wire subjected to bending at temperatures above A(f). These results are analyzed and discussed.