Abstract
NiTi shape memory alloy (SMA) tube was coupled with mild steel cylinder in order to investigate deformation mechanisms of NiTi SMA tubes undergoing radial loading. NiTi SMA tubes of interest deal with two kinds of nominal compositions; namely, Ni-50 at % Ti and Ni-49.1 at % Ti, where at room temperature, B19′ martensite is dominant in the former, and B2 austensite is complete in the latter. The mechanics of the NiTi SMA tube during radial loading were analyzed based on elastic mechanics and plastic yield theory, where effective stress and effective strain are determined as two important variables that investigate deformation mechanisms of the NiTi SMA tube during radial loading. As for the NiTi SMA tube with austenite structure, stress-induced martensite (SIM) transformation as well as plastic deformation of SIM occur with the continuous increase of effective stress. As for NiTi SMA tube which possesses martensite structure, reorientation and detwinning of twinned martensite as well as plastic deformation of reoriented and detwinned martensite occur with the continuous increase in the effective stress. Plastic deformation for dislocation slip has a negative impact on superelasticity and shape memory effect of NiTi SMA tube.
Highlights
NiTi shape memory alloy (SMA) has been substantially employed in the domain of engineering since it possesses perfect shape memory effect (SME) and excellent superelasticity [1]
Based on SME, NiTi SMA can remember the shape in the austenite phase when it is heated to austenite finish temperature (Af ) after undergoing a certain extent of deformation in the martensite state
The deformation mechanics belongs to thetube axisymmetric well as the plane stress problem, mechanics of tube belongs to the axisymmetric problem as well as the plane stress where the axial stress σz is equal to zero without the axial loading, and the radial stress σ p problem, and the where the axial stress σz is equal to zero without the axial loading, and the radial stress σp and the tangential stress σθ are irrespective of the axial coordinate axis
Summary
NiTi shape memory alloy (SMA) has been substantially employed in the domain of engineering since it possesses perfect shape memory effect (SME) and excellent superelasticity [1]. Sun and Li studied the mechanical behavior of B2 austenite NiTi SMA tube under simple tension and simple shear [11,12] They found that when NiTi SMA tube with B2 austenite undergoes simple tension, SIM transformation occurs so that a martensitic spiral band can be observed. NiTi SMA tube with B2 austenite suffers from simple shear, a martensitic spiral band cannot be observed. NiTi tube under simple tension was further validated on the found that in the case of uniaxial compression, a homogeneous martensite phase transformation basis of experimental observation. NiTi SMA tube bending can Bechle lead to Kyriakides localized nucleation of martensite where exhibit subjected to bending load They found that lead to localized nucleation the considerable difference between the compression andbending tensioncan sides [16].
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