Experimental study of one‐dimensional superelastic capability of a nearly equi‐atomic NiTi shape memory alloy

Abstract

A series of experimental studies have been carried out on nearly equi-atomic NiTi shape memory alloy wires. The effects of fatigue cycles, displacement rates as well as testing temperatures on the superelastic capabilities have been studied. Under cycling loading, the threshold stresses for martensitic transformation decrease and the residule strains increase. Saturation is reached after 100 cycles. With increasing displacement rates, the critical stresses required for the martensitic transformation increase and the slopes of the upper plateau in the stress-strain curves rise. The dissipated energy increases rapidly with increasing displacement rate, reaches a maximum value at around 6.0mm/min and then decreases as the displacement rate continues to increase. Tests also show that the threshold stresses characterizing the forward/reverse transformations increase linearly with increasing test temperature.

Large scale simulation of NiTi helical spring actuators under repeated thermomechanical cycles

“…In applications, shape memory alloys are commonly utilized in two fundamentally different ways: (i) making use of the superelasticity/pseudoelasticity (SE/PE) phenomena (Nemat-Nasser and Guo 2006, Wang et al 2005, Zhu et al 2004, as in applications in biomedical engineering, and (ii) taking advantages of the shape memory effect (SME) (Stebner et al 2009, Jones andDye 2011), as is used for actuators. The key to these unique SE/PE and SME properties is the solid-to-solid, diffusionless martensitic phase transformation between a high-symmetry austenite phase (A-parent) and low-symmetry martensite phase (M-daughter) under the effect of temperature and/or stress.…”

“…Research involving SMAs can be grouped into three main areas: (a) experimental work, (b) constitutive modeling efforts, and (c) analytical/computational studies for boundary value problems involving structural components and/or SMA devices. From the standpoint of the experimental investigations conducted to date, much has been done to understand the deformation response of various forms, including wires, rods, and thin-walled tubes under conditions of both uniaxial and biaxial loadings within the pseudoelastic/pseudoplastic, as well as the shape memory effect regimes of various SMA material systems (Nemat-Nasser and Guo 2006, Adharapurapu et al 2006, Jones and Dye 2011, Kockar et al 2008, Wang et al 2005, Zhu et al 2004. In addition, more recently the emphasis has been on the study of the evolutionary response of these SMA material systems under a variety of isothermal and non-isothermal load cycles (Kang et al 2009;Padula II et al 2011).…”