Compressive superelastic behavior of a NiTi shape memory alloy at strain rates of 0.001-750 s-1

The compressive stress-strain behavior of a NiTi shape memory alloy (Nitinol SE508) has been determined over strain rates of 10(3)-7.5 x 10(2) s(-1). A hydraulically driven load frame (Material test system, MTS 810) was used to conduct the quasi-static experiments. A split Hopkinson pressure bar with a pulse shaping technique was used to perform valid dynamic tests. Experimental results show that, the plateau stress of the shape memory alloy (SMA) is strain-rate dependent. Under quasi-static deformation and low-amplitude impact loading, the stress-strain curve of the SMA forms a closed hysteresis loop, with the material returning to its original length upon unloading. At higher dynamic loads, there is initially a residual deformation upon unloading, but the material slowly recovers its length. Dynamic strain lags behind the associated dynamic stress in the SMA specimen. (C) 2001 Elsevier Science Ltd. All rights reserved.