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This paper presents an investigation of the influence of strain rate on the functional behaviour of TiNi alloy. Specimens were deformed in compression and tension modes using the Kolsky method for ...

The influence of aging of TiNi-based shape memory alloy (SMA) specimens on the one-way and two-way shape memory (TWSM) is studied experimentally and simulated with the use of a microstructural model. Experiments show that a long-time storage of preliminarily strained TiNi specimens does not change the strain recovery on heating. At the same time, the strain stroke due to the realization of the TWSM is bigger than before aging. Computer modeling of these phenomena is done within the frames of a microstructural model, in which the macroscopic strain is considered to be the average of the micro-strains–strains of micro-volumes. The irreversible strains are described from the standpoint of the plastic flow theory. Isotropic hardening and kinematic hardening are taken into account and are related to scattered and oriented deformation defects. To describe the effects of aging, special terms are introduced into the evolution equations for the defect densities. Thus, modified equations are able to account for a decrease of the yield limit due to a decrease of the deformation defect densities. The results of modeling show a good qualitative agreement with the experimental data, particularly an increase of the TWSM deformation after aging.

This study makes use of the magnetic pulse method for providing the uniaxial tension of TiNi shape memory alloy specimens. Finite element simulations demonstrate good agreement between the evaluated residual strains and experimental values. The evaluated average strain rates are ~ 4000–5000 s−1 and in local areas, they reach 10,000–12,000 s−1. The functional properties of the alloy after magnetic pulse tension are shown and compared with the results after quasistatic tension. The values of the shape memory effect after magnetic pulse tension decrease by 15–20%. Magnetic field simulation shows that induced currents are negligible and do not lead to heating in the working part of the specimens. It is concluded that the reason for the decrease in the shape memory effect is the high pre-strain rate. Reorientation processes must be sensitive to the strain rate, so the proportion of the oriented martensite decreases with increasing strain rate.