Anisotropic behavior of superelastic NiTi shape memory alloys; an experimental investigation and constitutive modeling

摘要

The effect of boundary condition on the mechanical behavior of superelastic NiTi shape memory alloys is investigated in this paper. Experimental tests were carried out on NiTi tubes subjected to tension and torsion with different boundary conditions including fixed and free end cases. Results revealed that anisotropy strain/stress appears in the material depending on the end boundary condition of the sample when martensite transformation occurs. This phenomenon is believed to be a result of anisotropy developed in NiTi during material processing and/or training procedures. Based on experimental findings, a new extension is considered to a 3-D phenomenological constitutive model to capture the anisotropic transformation strain/stress generation observed during different loading conditions. Numerical correlations between predicted and experimental data demonstrate the success of the modified model.