Microstructures and Mechanical Properties of Equiatomic NiTi Shape Memory Alloy Undergoing Local Canning Compression and Subsequent Annealing

Dong Sun,Shuyong Jiang,Xiaodong Xing,Bingyao Yan,Junbo Yu,Yanqiu Zhang 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.12

Local canning compression is imposed on equiatomic NiTi shape memory alloy (SMA) with complete B19′ martensite. Afraction of retained nanocrytalline grains are embedded in the dominant amorphous phase. The compressed NiTi samples areannealed for 2 h at various temperatures, including 300, 450 and 600 °C. Grain size increases with increasing crystallizationtemperature during heat treatment. Under annealing at 300 °C, nanocrystalline grains are dominant in NiTi SMA, where thereexists local amorphous zone. Under annealing at 450 °C, almost complete nanocrystalline can be obtained. Under annealingat 600 °C, grain size increases substantially, but there still exists a small amount of nanocrystalline grains. Under annealingat 300 °C, NiTi SMA exhibits extremely high elastic limit, but its plasticity is poor. Under annealing at 450 °C, NiTi SMAexhibits very high yield stress and it simultaneously keeps high plasticity. Under annealing at 600 °C, NiTi SMA exhibitsrelatively low yield stress, but its yield stress is still higher than that of as-received NiTi SMA and its plasticity is also high.

INVESTIGATION OF OCCUPANT LOWER EXTREMITY INJURES UNDER VARIOUS OVERLAP FRONTAL CRASHES

Fuhao Mo,Shuyong Duan,Xiaoqing Jiang,Sen Xiao,Zhi Xiao,Wei Shi,Kai Wei 한국자동차공학회 2018 International journal of automotive technology Vol.19 No.2

Objective: With widely usage of restraint system, fatal injuries to occupants have been largely limited while non-fatal lower extremity injuries have not been effectively improved. The present study aims to investigate occupant lower extremity injuries under realistic impact environments. Methods: A biofidelic lower extremity model, a dummy model and a car cab model were combined to set up a realistic impact environment. Three typical frontal impact groups were simulated. Occupant global lower kinematics, long bone axial force and bending moment were presented to in-depth investigate lower extremity injury mechanism and tolerance. Results: Various overlap frontal impacts cause totally different lower extremity kinematics in the combination of structural invasion and restraint system effects. The femur fracture occurred at a small axial force of 7.57 kN combing a substantial bending moment peak of 172 Nm. Ankle joint injuries were found in 100 % and 25 % overlap impacts that present large tibial axial force and joint rotation angle. Conclusions: Overall results indicate that a coupling threshold of femur axial force and bending moment is of rationality to predict global femur fracture. The ankle joint injury occurrence is significantly related to the coupling effects of tibia axial force and excessive self-kinematics.

Crystal Plasticity Finite Element Simulation of NiTi Shape Memory Alloy Based on Representative Volume Element

Li Hu,Shuyong Jiang,Yanqiu Zhang,Dong Sun 대한금속·재료학회 2017 METALS AND MATERIALS International Vol.23 No.6

Crystal plasticity finite element method based on a representative volume element model, which includes the effectof grain shape and size, is combined with electron backscattered diffraction experiment in order to investigate plasticdeformation of NiTi shape memory alloy during uniaxial compression at 400 °C. Simulation results indicatethat the constructed representation of the polycrystal microstructure is able to effectively simulate macroscopicallyglobal stress-strain response and microscopically inhomogeneous microstructure evolution in the case ofvarious loading directions. According to slip activity and Schmid factor in {110}<100>, {010}<100> and{110}<111> slip modes, <100> slip modes are found to play a dominant role in plastic deformation, while <111>slip mode is found to be a secondary slip mode. In addition, the simulation results are supported well by the experimentalones. With the progression of plastic deformation, the (001) [010] texture component gradually disappears,while the γ-fiber (<111>) texture is increasingly enhanced.

Influence of heat treatment on complex-shape rotating disk subjected to isothermal precision forging

Yanqiu Zhang,Shuyong Jiang,Xiaoming Zhu,Yanan Zhao,Debin Shan 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.1

Influence of heat treatment on the mechanical properties of the forging was systematically investigated according to tensile test, hardness test and electrical conductivity test. Simultaneously, typical microstructures of the 7A09 aluminum alloy samples subjected to various solution temperatures and aging regimes were characterized by means of Transmission electron microscope (TEM) and Scanning electron microscope (SEM). In the case of the different solution temperatures, the size of precipitations increases with the increase in the solution temperature, which contributes to improving both strength and stress corrosion resistance of the forging. The solution temperature of 465 °C leads to the well comprehensive mechanical properties and the superior stress corrosion resistance of the forging. G.P. zone, η' phase and η phase are able to precipitate in the matrix of the forging in the case of different aging regimes, such as peak aging, two-stage overaging, two-stage aging, and regression and re-aging. The precipitation phases play an important role in enhancing the mechanical properties of the forging as an obstacle against the dislocation movement.

Subgrain Effect on Grain Scale Plasticity of NiTi Shape Memory Alloy Under Canning Compression: A Crystal Plasticity Finite Element Analysis

Li Hu,Shuyong Jiang,Jian Tu,Zhiming Zhou 대한금속·재료학회 2019 METALS AND MATERIALS International Vol.25 No.2

The subgrain effect of NiTi shape memory alloy during canning compression at 400 °C is investigated through electronback-scattered diffraction (EBSD) experiment, transmission electron microscope (TEM) experiment and crystal plasticityfinite element (CPFE) simulation in explicit consideration of subgrain within each grain. Experimental investigations basedon TEM and EBSD measurements confirm that the formation of subgrain actually results from the dislocation motion duringcanning compression. Numerical simulations based on the constructed polycrystalline models with various subgrains areused to investigate the subgrain effect during canning compression from a different point of view. In terms of texture evolution,subgrain effect does not change the tendency of texture evolution, but it contributes to the dispersed distribution withrespect to the deformed grain/subgrain orientations. As for accumulative shear strain, subgrain effect contributes to sustaininglarger plastic strain inside each grain, and it also results in the strain concentration near grain boundaries. With respectto von Mises stress, the subgrain effect facilitates the ease of stress concentration near grain boundaries and it contributesto possessing a homogeneous stress distribution within the inner part of each grain.

Investigation on Texture Evolution Mechanism of NiTiFe Shape Memory Alloy Under Plane Strain Compression

Yulong Liang,Qiang He,Shuyong Jiang,Chengzhi Zhao 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.10

Texture evolution of NiTiFe shape memory alloy (SMA) is investigated during plane strain compression based on crystalplasticity finite element method (CPFEM) and electron back-scatter diffraction (EBSD) experiment. The deformation texturesof NiTiFe SMA are not influenced very considerably after experiencing recrystalline annealing at 600 °C for 1 h. Based onthe results of CPFEM, the main activated slip systems of NiTiFe SMA are ⟨100⟩/{110} and ⟨111⟩/{110} ones during planestrain compression. According to the relationship between texture components and activated slip systems put forward in thisstudy, ⟨110⟩ direction would rotate to rolling direction, whereas ⟨100⟩ and ⟨111⟩ directions would rotate to normal direction. These rotations contribute to the formation of γ-fibre texture and α-fibre texture in NiTiFe SMA. The deformation texturecomponents predicted by CPFEM and determined by EBSD were compared with each other in detail. Due to the startupof the pencil glide and multiple slip in the refined microstructure, there are some differences between texture componentspredicted by CPFEM and texture components determined by EBSD. The deformation heterogeneity is discussed in termsof rotation angle at each integration point in the study.

Influence of In-Plane Simple Shear Strain on the Grain Orientation Regulation and Stretch Formability of Pre-twinned AZ31 Magnesium Alloy Sheet

Liangliang Xue,Lifei Wang,Pengbin Lu,Qiang Zhang,Hua Zhang,Guangsheng Huang,Liwei Lu,Liuwei Zheng,Hanuma Reddy Tiyyagura,Hongxia Wang,Shuyong Jiang,Kwang Seon Shin 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.10

Pre-twin is widely accepted as an efficient method for weakening the basal texture to improve the plasticity of magnesium alloys, particularly for formability. However, the enhancement is limited since the largest Schmid factor (SF) of basal slip cannot be achieved. In-plane simple shear strain is used to control the twin orientation in accordance with Schmid law to further decrease the basal texture and improve the formability of the Mg alloys sheet. Consequently, secondary regulation of initial twin orientation (SRITO) technology, a novel combination procedure, was developed. In this method, the AZ31 Mg alloys sheet is compressed to pre-twins with various volumes (1%, 3%, and 5%), then the twin orientation is regulated by in-plane simple shear strain for the second time. Compared with the as-received sample, the average fracture elongation of the annealed sample with the best properties improves from 15.3 to 28.8%, and the Erichsen value increases from 2.8 to 6.1 mm due to the regulation of twin orientation.