Papers by Keyword: Stress-Induced Martensitic Transformation

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Authors: Takeshi Iwamoto, Mohammed Cherkaoui, Esteban P. Busso
Abstract: In this study, the simulation of the motion of an interface during the stress-induced martensitic transformation of a shape memory alloy is performed using the level-set method. The kinetics of the phase transformation is defined as an anisotropic kinetic relation between the rate at which the weak discontinuity moves, given by its normal velocity, and the thermodynamics driving force. The latter is derived from a dissipation function, which obeys the 1st and 2nd law of thermodynamics and accounts for large strains. Furthermore, a hyperelastic constitutive framework is used to describe the constitutive behavior of the material. The model is implemented into the finite element method and is then used to solve a 2D phase transformation problem in a shape memory alloy.
Authors: Bashir S. Shariat, Yinong Liu, Gerard Rio
Abstract: This study presents a numerical model for deformation behaviour of near-equiatomic NiTi holey plates using finite element method. Near-equiatomic NiTi alloy deforms via stress-induced AM martensitic transformation, which exhibits a typical hystoelastic mechanical behaviour. In this model, the transformation stress is decomposed into two components: the hyperelastic stress, which describes the main reversible aspect of the deformation process, and the hysteretic stress, which describes the irreversible aspect of the process. It is found that with increasing the level of porosity of the holey plate, the nominal stress for the AM transformation decreases and the strain increases. In addition, the stress-strain slope over the stress plateau also increases with increasing the porosity. While the porosity level has a strong effect on global stress-strain behaviour of the holey plate, regularity of the arrangement of the holes is found to have negligible effect.
Authors: Tae Hyun Nam, Hyun Gon Kim, Ju Young Choi, Jung Moo Lee, Suk Bong Kang, Cha Yong Lim
Abstract: Deformation behavior of temperature gradient anneal(TGA) treated Ti-50.0Ni(at%) alloys were investigated by means of thermal cycling tests under constant load and tensile tests. TGA treated Ti-Ni alloy wires showed a sequential deformation behavior along the length of the specimen since the stress required for the B2-B19’ transformation increased with decreasing annealing temperature. Considerably large residual elongation(about 0.4 %) occurred in the TGA treated Ti-Ni alloy under the applied stress of 80 MPa, which is ascribed to the fact that yield stress of the sample annealed at 823 K is lower than the stress required for the B2-B19’ transformation of the sample annealed at 658 K.
Authors: Yonosuke Murayama, Hiroto Shioiri
Abstract: Metastable beta Ti-Cr-Sn-Zr alloys used as biomaterial show low Young’s modulus and super-elasticity according to the phase stability of their beta phase. In this study, we substituted Nb and Fe for Cr in metastable beta Ti-2Cr-6Sn-45Zr alloy and investigated their effect. We investigated how the added amount of Cr, Nb and Fe influences the phase stability and the properties of low Young’s modulus and super-elasticity in Ti-x-Sn-Zr (x=Cr, Nb or Fe) alloys. The Young’s modulus of a Ti-x-Sn-Zr (x=Cr, Nb or Fe) alloy decreases with the addition of Cr, Nb or Fe. However, the Young’s modulus of a Ti-x-Sn-Zr (x=Cr, Nb or Fe) alloy increases with the addition of Cr, Nb or Fe after showing own minimum value respectively. Minimum Young’s modulus of several Ti-x-Sn-Zr (x=Cr, Nb or Fe) alloys were under 50GPa. The required amount of Cr, Nb or Fe in the Ti-x-Sn-Zr (x=Cr, Nb or Fe) alloy having minimum Young’s modulus is different according to the beta stabilizing ability of each element. Fe amounts were the smallest and Nb amounts were the largest. Ti-x-Sn-Zr (x=Cr, Nb or Fe) alloy with minimum Young’s modulus shows a stress-induced martensitic transformation. However, only Ti-Cr-Sn-Zr alloys showed definite super-elasticity. The recovered strain by super-elasticity is small in Ti-Nb-Sn-Zr alloy. Ti-Fe-Sn-Zr alloy didn’t show super-elasticity or large elongation.
Authors: Tokunaga Hitoo, Fujita Kazutaka, Yokoyama Yoshihiko
Abstract: Zr-Cu-Al bulk metallic glass matrix composite with the intermetallic compound ZrCu (B2) phase was fabricated. The effect of the ZrCu phase on mechanical properties and deformation behavior of the composite was investigated by compressive test. Also, phase transformation behavior of the ZrCu phase was analyzed by X-ray diffraction. Furthermore, macroscopic shape memory behavior was investigated using the composite by three point bending test. As the results, it was found that the mechanical properties of the composite depend on the volume fraction of the precipitated ZrCu phase. Compressive strength and yield stress of the composite decrease with increase of volume fraction of the ZrCu phase. On the other hand, plastic strain increases with increase of volume fraction of the ZrCu phase. In addition, it was confirmed that a stress-induced martensitic transformation of the ZrCu phase occurs by compressive stress loading. Furthermore, it was found that the composite with high volume fraction of the ZrCu phase exhibits shape memory effect.
Authors: Alaa Mahmoud Keshtta, Mohamed Abdel Hady Gepreel
Abstract: Recently, Ni-free shape memory Ti-based alloys (composed of the biocompatible β-stabilizing elements such as Ta and Nb) are extensively studied. In this work, new Ni-free Ti-17Nb-6Ta is presented as a candidate for shape memory alloys with high biocompatibility. This alloy produced using arc-melting in argon atmosphere, followed by solution annealing at 900° C for 30 min. β-phase is the predominant phase beside α” martensite phase. Stress induced martensitic transformation is observed after cold rolling and during bending tests as measured by XRD. The hardness of the bended wire in the solution treated condition was around 330HV. While the cold rolled wire hardness before bending was 300 HV. The superelasticity and shape memory effect was investigated through bending tests of alloy wires. The cold rolled wire showed higher superelasticity than shape memory effect. But superelasticity and the shape memory effect were almost similar with the solution treated wire. Also, the total spring back in cold rolled wire is higher compared with solution treated wire.
Authors: L.H. Liu, Wei Cai, Xiang Long Meng, Y.F. Zheng, Yong Xing Tong, Lian Cheng Zhao, Li Min Zhou
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