The functional properties of shape memory alloys depend on the strain rate. However, there is no systematic investigation of the basic functional properties after high strain rate deformation; most of the published articles, including modern studies, focus on the mechanical properties and structure. This paper presents a study of the influence of strain rate on the one-way and two-way shape memory effects. The specimens were compressed at strain rates of 500, 1200, 1600 s?1 in the martensitic, austenitic, and mixed-phase state, using the Kolsky method for the split Hopkinson pressure bar. The one-way and two-way shape memory effects were measured after dynamic compression and compared with ones after quasi-static compression up to the same residual strains. The work shows that the strain rate has significant influence on the basic functional properties of the NiTi alloy. In some cases, the strain-temperature curves after the quasi-static and dynamic compression were completely different. The one-way shape memory effect after high-strain rate compression was less than after quasi-static compression, irreversible strain increased. After high-strain rate compression in the martensitic state, the martensitic two-way shape memory effect slightly grows, but in general, there is no significant improvement. The austenitic two-way shape memory effect after high strain rate compression occurred at lower test temperatures, and its value was higher than after quasi-static compression. Thus, in some cases, the functional properties of the NiTi alloy can be improved by an increase in the strain rate. The material behavior indirectly demonstrates that the reorientation of martensite and the formation of stress-induced martensite are sensitive to the strain rate.
展开▼
