The compressive response of a NiTi shape-memory alloy is investigated at various strain rates using UCSD’s modified Hopkinson pressure bar and a conventional Instron machine. To obtain a constant strain rate during the formation of a stress-induced martensite in a Hopkinson test, a copper tube of suitable dimensions is employed as a pulse shaper, since without a pulse shaper the strain rate of the sample varies significantly as its microstructure changes from austenite to martensite, whereas with proper pulse shaping techniques a nearly constant strain rate can be achieved over a certain deformation range. The NiTi shape-memory alloy shows a superelastic response for small strains at all considered strain rates and at room temperature, 296 K. At this temperature and below a certain strain rate, the stress–strain curves of the NiTi shape-memory alloy display two regimes: an elastic austenite regime and a transition (stress-induced martensite) regime. The transition stress of this material and the work-hardening rate in the stress-induced martensite regime increase with increasing strain rate, the latter reaching a steady state level and then rapidly increasing.
High Strain-Rate, Small Strain Response of a NiTi Shape-Memory Alloy
Manuscript received February 4, 2004; revision received September 23, 2004. Review conducted by: M. Cherkaoui.
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Nemat-Nasser, S., Yong Choi , J., Guo , W., Isaacs, J. B., and Taya, M. (February 22, 2005). "High Strain-Rate, Small Strain Response of a NiTi Shape-Memory Alloy ." ASME. J. Eng. Mater. Technol. January 2005; 127(1): 83–89. https://doi.org/10.1115/1.1839215
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