The review on effect of a high strain rate on the properties of TiNi-shape memory alloys is presented. The study of thermo-mechanical and functional properties of SMA after high strain rate loading was carried out. The object of study was an equiatomic TiNi shape memory alloy. The samples were tensioned at a strain rate of about 103s-1at various temperatures in martensitic, austenitic, and two-phase state, using the Split Hopkinson Pressure Bar technique. Two-way shape memory effects were investigated. Two-way shape memory after high strain rate loading was less than after the quasi-static one for all cases, except for straining in martensitic state.
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 a split Hopkinson pressure bar, and its modification in martensitic, austenitic, and pre-martensitic states at 500, 1000, and 1500 s−1 strain rates. One-way shape memory and two-way shape memory (TWSM) effects were measured and compared with ones after quasi-static deformation. With an increase in the strain rate, the one-way shape memory effect decreased, but the TWSM effect increased. Functional behaviour indirectly demonstrated the sensitivity of the martensite reorientation and the formation of stress-induced martensite to strain rate. Strain rate sensitivity led to differences in the shape recovery curves during thermocycling.
Magnetic-pulse loading methods have been known since the 80s of the XX century and, as a rule, are used to determine the laws of destruction of materials under the action of pressure pulses with a duration of several microseconds. A modified scheme of a magnetic-pulse setup for high strain rate uniaxial tension is used in this work. The application of the scheme with the possibility of experimental measurement of the strain accumulation time and strain rate is shown on samples of TiNi alloy. The paper presents the results of finite element modeling and analytical description. Both approaches have demonstrated good agreement between the calculated residual strain and experimental results, even on samples of TiNi alloy with a specific stress-strain diagram. The analytical solution showed good qualitative agreement in assessing the strain accumulation time. On the basis of the analytical solution, an assessment of the capabilities of the magnetic-pulse loading method for uniaxial high strain rate tension is presented.
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