scholarly journals Molecular Dynamics Investigation of the Influence of Voids on the Impact Mechanical Behavior of NiTi Shape-Memory Alloy

Materials ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 4020
Author(s):  
Zhenwei Wu ◽  
Xiang Chen ◽  
Tao Fu ◽  
Hengwei Zheng ◽  
Yang Zhao
Keyword(s):  
Shock Wave ◽  
Molecular Dynamics ◽  
Plastic Deformation ◽  
Phase Transformation ◽  
Shape Memory Alloy ◽  
Shock Waves ◽  
Mechanical Behavior ◽  
Shape Memory ◽  
Wave Front ◽  
Niti Sma

To date, research on the physical and mechanical behavior of nickel-titanium shape-memory alloy (NiTi SMA) has focused on the macroscopic physical properties, equation of state, strength constitution, phase transition induced by temperature and stress under static load, etc. The behavior of a NiTi SMA under high-strain-rate impact and the influence of voids have not been reported. In this present work, the behavior evolution of (100) single-crystal NiTi SMA and the influencing characteristics of voids under a shock wave of 1.2 km/s are studied by large-scale molecular dynamics calculation. The results show that only a small amount of B2 austenite is transformed into B19’ martensite when the NiTi sample does not pass through the void during impact compression, whereas when the shock wave passes through the hole, a large amount of martensite phase transformation and plastic deformation is induced around the hole; the existence of phase transformation and phase-transformation-induced plastic deformation greatly consumes the energy of the shock wave, thus making the width of the wave front in the subsequent propagation process wider and the peak of the foremost wave peak reduced. In addition, the existence of holes disrupts the orderly propagation of shock waves, changes the shock wave front from a plane to a concave surface, and reduces the propagation speed of shock waves. The calculation results show that the presence of pores in a porous NiTi SMA leads to significant martensitic phase transformation and plastic deformation induced by phase transformation, which has a significant buffering effect on shock waves. The results of this study provide great guidance for expanding the application of NiTi SMA in the field of shock.

scholarly journals Phase Transformation, Twinning, and Detwinning of NiTi Shape-Memory Alloy Subject to a Shock Wave Based on Molecular-Dynamics Simulation

Materials ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 2334 ◽  
Author(s):  
Man Wang ◽  
Shuyong Jiang ◽  
Yanqiu Zhang
Keyword(s):  
Shock Wave ◽  
Molecular Dynamics ◽  
Molecular Dynamics Simulation ◽  
Martensitic Transformation ◽  
Shape Memory Alloy ◽  
Shape Memory ◽  
Dynamics Simulation ◽  
Repeated Loading ◽  
Reverse Martensitic Transformation ◽  
Niti Sma

Martensitic transformation, reverse martensitic transformation, twinning, and detwinning of equiatomic nickel–titanium shape-memory alloy (NiTi SMA) under the action of a shock wave are studied using a molecular-dynamics simulation. In the loading process of a shock wave, B2 austenite is transformed into B19′ martensite, whereas in the unloading process of the shock wave, B19′ martensite is transformed into B2 austenite. With repeated loading and unloading of the shock wave, martensitic transformation occurs along with twinning, but reverse martensitic transformation appears along with detwinning. The mechanisms for the twinning and detwinning of NiTi SMA subjected to a shock wave are revealed in order to lay the theoretical foundation to investigate the shape-memory effect and superelasticity.

scholarly journals One-Dimensional Constitutive Model of Shape Memory Alloy with an Empirical Kinetics Equation

2011 ◽  
Vol 2011 ◽  
pp. 1-14 ◽  
Author(s):  
Lei Li ◽  
Qingbin Li ◽  
Fan Zhang
Keyword(s):  
Plastic Deformation ◽  
Phase Transformation ◽  
Shape Memory Alloy ◽  
Constitutive Model ◽  
Shape Memory ◽  
Uniaxial Tension ◽  
Experimental Results ◽  
Kinetics Equation ◽  
One Dimensional ◽  
Niti Sma

Characteristics of NiTi shape memory alloy (SMA) and its constitutive model with an empirical kinetics equation were investigated in this paper. Firstly, the transformation characters of the NiTi SMA were obtained through a differential scanning calorimetry (DSC) analysis technology, and the properties during incomplete and discontinuous transformation process and the effects of plastic deformation on the transformation were studied. The uniaxial tension, SME, and constrained recovery process of NiTi SMA were examined through an improved 10KN universal material testing machine. Experimental results indicated that the phase transformation characters and the mechanical properties could be affected by the loading process considerably, and the plastic deformation should be taken into account. To simulate the characteristics of NiTi SMA more effectively, a one-dimensional constitutive model derived from the internal variable approach with the consideration of the plastic deformation was constructed based on the DSC and the uniaxial tension experimental results, and a new simple empirical kinetics equation was presented, with the transformation temperature parameters redefined according to the DSC experiment evidence. Comparison between the numerical and experimental results indicated that this constitutive model could simulate the phase transformation characters, the uniaxial tension, SME, and the constrained recovery behavior of NiTi SMA well.

scholarly journals Finite Element Simulation of NiTiNb Shape Memory Alloy Pipe-Joint Subjected to Coupled Transformation and Plastic Deformation

2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Xiang Chen ◽  
Bin Chen ◽  
Xianghe Peng ◽  
Xiaoqing Jin ◽  
Ying Ma ◽  
...  
Keyword(s):  
Plastic Deformation ◽  
Phase Transformation ◽  
Shape Memory Alloy ◽  
Shape Memory ◽  
High Performance ◽  
Coupling Effect ◽  
Longitudinal Direction ◽  
Design Parameters ◽  
Pull Out ◽  
Pipe Joint

The assembling process of Ni47Ti44Nb9 alloy pipe joints considering the phase transformation and plasticity was numerically simulated for the first time with a developed constitutive model. The simulated process was based on the experimental material parameters, which were determined with the experimental tensile results of Ni47Ti44Nb9 shape memory alloy (SMA) and steel bars. The results showed that, after assembly, the Mises stress distributed uniformly along the longitudinal direction of the NiTiNb joint, but nonuniformly along the radial direction. The maximum σeq does not appear at the inner wall of the joints due to the coupling effect of the plastic deformation and the recoverable transformation. The contact pressure distributed uniformly along the circumferential direction, but nonuniformly along the longitudinal direction. The sizes of the SMA joint and the pipe should be properly matched to ensure contact during the stage of the rapid reverse phase transformation to obtain stable connection performance. The pull-out force was also computed, and the results were in good agreement with the experimental results. The results obtained can provide available information for the optimization of the design parameters of the high-performance SMA pipe-joint, such as inner diameter and assembly clearance.

Investigation on Mechanical Behaviors of Shape Memory Alloy Torsion Rod

2011 ◽  
Vol 179-180 ◽  
pp. 455-458
Author(s):  
Bo Zhou ◽  
Zhen Qing Wang ◽  
Yan Ju Liu ◽  
Jin Song Leng
Keyword(s):  
Phase Transformation ◽  
Constitutive Equation ◽  
Shape Memory Alloy ◽  
Shape Memory ◽  
Martensitic Phase Transformation ◽  
Mechanical Behaviors ◽  
Transformation Temperatures ◽  
Mechanics Of Materials ◽  
Niti Sma ◽  
The Relationship

DSC test is carried out to determine the phase transformation temperatures of a NiTi SMA, which include martensitic starting temperature, martensitic finishing temperature, austenitic starting temperature and austenitic finishing temperature. The mechanical behaviors of shape memory alloy (SMA) torsion rod are investigated by using Zhou’s shear constitutive equation of SMA and the theorem of circular shaft in mechanics of materials. A critical torque equation is developed to describe the relationship between the martensitic phase transformation critical torque of SMA torsion rod and temperature.

Mechanical Behavior of an Ni-Ti Shape Memory Alloy Under Axial-Torsional Proportional and Nonproportional Loading

1999 ◽  
Vol 121 (1) ◽  
pp. 9-18 ◽  
Author(s):  
T. Jesse Lim ◽  
David L. McDowell
Keyword(s):  
Phase Transformation ◽  
Shape Memory Alloy ◽  
Strain Rate ◽  
Mechanical Behavior ◽  
Shape Memory ◽  
Micromechanical Model ◽  
Numerical Differentiation ◽  
Thin Wall ◽  
Proportional Loading ◽  
Nonproportional Loading

Several biaxial proportional and nonproportional loading experiments are reported for thin-wall tubes of a pseudoelastic Ni-Ti shape memory alloy (SMA). In addition to the mechanical behavior, temperature was measured during the experiments. It is shown that the phase transformation exhibits asymmetrical behavior in the case of tension-compression cycling. The transformation strain rate is determined for selected histories by numerical differentiation of data. Under nonproportional loading, the rate of phase transformation does not follow a generalized J2-J3 criteria based on results of micromechanical simulations for proportional loading. The role of simultaneous forward and reverse transformations on the nonproportional transformation response is examined using a simple micromechanical model, and the direction of the inelastic strain rate is adequately predicted. Load- and strain-controlled experiments at different strain rates, with and without hold times, are reported and coupled thermomechanical effects are studied.

Analysis of Thermo-Mechanical Behavior of Shape Memory Alloys

2010 ◽  
Vol 452-453 ◽  
pp. 149-152
Author(s):  
Hong Shuai Lei ◽  
Zhen Qing Wang ◽  
Bo Zhou ◽  
Yu Long Wang
Keyword(s):  
Phase Transformation ◽  
Numerical Calculation ◽  
Constitutive Equation ◽  
Shape Memory Alloy ◽  
Mechanical Behavior ◽  
Shape Memory ◽  
Transformation Behavior ◽  
Test Result ◽  
Optical Micrographs ◽  
Numerical Calculation Result

Shape Memory Alloy (SMA) is widely used and plays an important role in various engineering fields due to its special characteristics of shape memory effect and super-elasticity. In this paper the phase transformation behavior and thermo-mechanics behavior of 50.0at%Ni-Ti SMA are investigated though differential scanning colorimeter (DSC) and tensional tests respectively. Optical micrographs show the transformation of austenite and twinned martensite. The comparing numerical calculation result with tensional test result shows the new macro-mechanical constitutive equation can express the thermo-mechanical behavior of SMA effectively.

Investigation of shock-wave deformation history from recovered structure

1986 ◽  
Vol 44 ◽  
pp. 434-435
Author(s):  
M.A. Mogilevsky ◽  
L.S. Bushnev
Keyword(s):  
Shock Wave ◽  
Plastic Deformation ◽  
Dislocation Density ◽  
Shock Waves ◽  
Shock Front ◽  
Single Crystals ◽  
Residual Deformation ◽  
Deformation Structure ◽  
Deformation History ◽  
Deformation Velocity

Single crystals of Al were loaded by 15 to 40 GPa shock waves at 77 K with a pulse duration of 1.0 to 0.5 μs and a residual deformation of ∼1%. The analysis of deformation structure peculiarities allows the deformation history to be re-established.After a 20 to 40 GPa loading the dislocation density in the recovered samples was about 1010 cm-2. By measuring the thickness of the 40 GPa shock front in Al, a plastic deformation velocity of 1.07 x 108 s-1 is obtained, from where the moving dislocation density at the front is 7 x 1010 cm-2. A very small part of dislocations moves during the whole time of compression, i.e. a total dislocation density at the front must be in excess of this value by one or two orders. Consequently, due to extremely high stresses, at the front there exists a very unstable structure which is rearranged later with a noticeable decrease in dislocation density.

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