Abstract
To date, research on the physical and mechanical behavior of nickel-titanium shape-memory alloy (NiTi SMA) has focused on the macroscopic physical properties, equation of state, strength constitution, phase transition induced by temperature and stress under static load, etc. The behavior of a NiTi SMA under high-strain-rate impact and the influence of voids have not been reported. In this present work, the behavior evolution of (100) single-crystal NiTi SMA and the influencing characteristics of voids under a shock wave of 1.2 km/s are studied by large-scale molecular dynamics calculation. The results show that only a small amount of B2 austenite is transformed into B19’ martensite when the NiTi sample does not pass through the void during impact compression, whereas when the shock wave passes through the hole, a large amount of martensite phase transformation and plastic deformation is induced around the hole; the existence of phase transformation and phase-transformation-induced plastic deformation greatly consumes the energy of the shock wave, thus making the width of the wave front in the subsequent propagation process wider and the peak of the foremost wave peak reduced. In addition, the existence of holes disrupts the orderly propagation of shock waves, changes the shock wave front from a plane to a concave surface, and reduces the propagation speed of shock waves. The calculation results show that the presence of pores in a porous NiTi SMA leads to significant martensitic phase transformation and plastic deformation induced by phase transformation, which has a significant buffering effect on shock waves. The results of this study provide great guidance for expanding the application of NiTi SMA in the field of shock.
Highlights
Shape-memory alloys (SMAs) are alloy materials that recover their original shape before deformation by heating the material to a critical temperature and, at the same time, can have large recoverable elastic strain under unloading
When the shock wave passes through the hole, there is no propagation medium at the hole, so the shock wave needs to propagate forward along the edge of the hole, and the distance traveled by the shock wave increases
(2) Under the same impact loading conditions, the shock wave propagates uniformly in the non-porous sample, but when the shock wave passes through the hole region of porous material, the original hole region collapses, and a large number of defects and dislocations are formed
Summary
Shape-memory alloys (SMAs) are alloy materials that recover their original shape before deformation by heating the material to a critical temperature and, at the same time, can have large recoverable elastic strain under unloading. The porous NiTi shape-memory alloy is a highly dampened material for vibration damping, which has stronger damping properties than general metallic materials due to its large number of microporous structures and large number of grain boundaries in the tissue It has a greater prospect of application in vibration damping devices and is potentially valuable in reducing the effects of shocks and explosions [7,8,9]. With the development of macro- and microscopic numerical simulation techniques, reports on the microstructural evolution related to shapememory effect and super-elasticity have gradually increased [10,11,12] Most of these reports focus on the effects of static loading and temperature changes, with only a few reports on the phase transformation, twinning, and detwinning of NiTi SMAs under high strain rate impact loading. Gur et al [15] compared the simulation results for nanoporous NiTi with various porosity configurations with non-porous NiTi, finding that the martensite phase fraction and transformation temperature increase significantly with the increase in porosity, the stress-strain response changes significantly with the change in porosity, and the residual strain and hysteretic energy dissipation capacity increase significantly with the increase in porosity
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