Investigation of the stress-induced martensitic transformation in pseudoelastic NiTi under uniaxial tension, compression and compression–shear

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.

Section: Resultsmentioning

confidence: 99%

Investigation on Deformation Mechanisms of NiTi Shape Memory Alloy Tube under Radial Loading

Jiang

et al. 2017

“…Strain values during these tests were determined from the crosshead displacement data of the tensile testing machine. Localized deformation can be documented by diffraction methods, 2D or 3D local strain mapping as well as by infrared thermal imaging methods [39][40][41][42][43][44]. In the present study, the local deformation behavior of the investigated material conditions was characterized in greater detail by additional tensile tests in combination with digital image correlation (DIC).…”

Section: Introductionmentioning

confidence: 94%

“…Finally, a highly sensitive unidirectional stereo microphone (XYH-6 X/Y Capsule by Zoom™, Hauppauge, NY, USA, 24 bit, up to 96 kHz) was used in the same setup ( Figure 2) to measure acoustic emission signals (as integral acoustic intensity) based on earlier reports on acoustic emission related to PLC effects [2,3,15,18,[45][46][47]. Localized deformation can be documented by diffraction methods, 2D or 3D local strain mapping as well as by infrared thermal imaging methods [39][40][41][42][43][44]. In the present study, the local deformation behavior of the investigated material conditions was characterized in greater detail by additional tensile tests in combination with digital image correlation (DIC).…”

Section: Introductionmentioning

confidence: 99%

On the PLC Effect in a Particle Reinforced AA2017 Alloy

Härtel¹,

Illgen²,

Frint³

et al. 2018

Abstract:The Portevin-Le Châtelier (PLC) effect often results in serrated plastic flow during tensile testing of aluminum alloys. Its magnitude and characteristics are often sensitive to a material's heat treatment condition and to the applied strain rate and deformation temperature. In this study, we analyze the plastic deformation behavior of an age-hardenable Al-Cu alloy (AA2017) and of a particle reinforced AA2017 alloy (10 vol. % SiC) in two different conditions: solid solution annealed (W) and naturally aged (T4). For the W-condition of both materials, pronounced serrated flow is observed, while both T4-conditions do not show distinct serrations. It is also found that a reduction of the testing temperature (−60 • C, −196 • C) shifts the onset of serrations to larger plastic strains and additionally reduces their amplitude. Furthermore, compressive jump tests (with alternating strain rates) at room temperature confirm a negative strain rate sensitivity for the W-condition. The occurring PLC effect, as well as the propagation of the corresponding PLC bands in the W-condition, is finally characterized by digital image correlation (DIC) and by acoustic emission measurements during tensile testing. The formation of PLC bands in the reinforced material is accompanied by distinct stress drops as well as by perceptible acoustic emission, and the experimental results clearly show that only type A PLC bands occur during testing at room temperature (RT).

“…Binary NiTi shape memory alloy (SMA) has been extensively used in the engineering field due to its unique phenomena, which include a shape memory effect and superelasticity [1][2][3]. It is of great importance to add the third element to the binary NiTi SMA so as to broaden the engineering application [4][5][6].…”

Section: Introductionmentioning

confidence: 99%

Processing Map of NiTiNb Shape Memory Alloy Subjected to Plastic Deformation at High Temperatures

Wang

Jiang

Zhang

2017

Abstract:The processing map of Ni 47 Ti 44 Nb 9 (at %) shape memory alloy (SMA), which possesses B2 austenite phases and β-Nb phases at room temperature, is established in order to optimize the hot working parameters. Based on true stress-strain curves of NiTiNb SMA during uniaxial compression deformation at the temperatures ranging from 700 to 1000 • C and at the strain rates ranging from 0.0005 to 0.5 s −1 , according to dynamic material model (DMM) principle, the processing map of NiTiNb SMA is obtained on the basis of power dissipation map and instability map. The instability region of NiTiNb SMA increases with increasing the true strain and it mainly focuses on the region with high strain rate. The workability of NiTiNb SMA becomes worse and worse with increasing plastic strain, as well as decreasing deformation temperature. There exist two stability zones which are suitable for hot working of NiTiNb SMA. In one stability region, the deformation temperature ranges from 750 to 840 • C and the strain rate ranges from 0.0003 to 0.001 s −1 . In the other stability region, the deformation temperature ranges from 930 to 1000 • C and the strain rate ranges from 0.016 to 0.1 s −1 . The severe microstructure defects, such as coarsening grains, band microstructure, and intercrystalline overfiring appear in the microstructures of NiTiNb SMA which is subjected to plastic deformation in the instability zone.