Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Twinning induced plasticity (TWIP) steel exhibits high strength and exceptional plasticity due to the formation of extensive twin under mechanical load and its ultimate tensile strength and elongation to failureductility-value can be as high as 50000 MPa⋅%. Therefore, the TWIP steel can still maintain high energy absorption performance and impact resistance when its thickness is reducing to the half. The high work hardening plays a dominant role during deformation, resulting in excellent mechanical properties. The deformation mechanisms, responsible for this high work hardening, are related to strain-induced microstructural changes, which are dominated by slip and twinning. Different deformation mechanisms, which can be activated at different stages of deformation, will strongly influence stress-strain response and microstructure evolution. In order to understand the effects of slip and twinning during plastic deformation process, it is important to explore the microstructure evolution of those two deformation mechanisms and their influences on macroscopic deformation during this process. In this work, a crystal plasticity constitutive model of TWIP steel coupling slip and twinning was developed based on the crystal plasticity theory. In this model, the volume fraction of twin and its saturation value were introduced in order to consider the effect of twinning on hardening and slip, respectively. The constitutive model was implemented and programed based on the ABAQUS/UMAT platform. It was applied to simulate the plastic deformation process of single crystal for typical orientation microstructures under simply loading condition. The microscopic mechanism of plastic deformation of single crystals with different orientations was analyzed, and then the influence of slip-twinning system startup states on macroscopic plastic deformation was investigated. The saltation of stress for brass and S orientations was paid attention especially, the stress steep fall for copper single crystal was also reproduced during tensile tests. The results show that when the volume fraction of twin is small, its effect on strain hardening should be ignored; however, its impact becomes gradually obvious with the increase of volume fraction of twin; when the volume fraction of twin reaches saturation value, twinning increment is zero, the slip directions in crystal must change, another slip system will be activated as a result of stress dropping suddenly.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Mg alloy has hexagonal structure and exhibits poor workability at room temperature, which is attributed to the difficulty in activating a sufficient number of independent slips to accommodate the deformation. Twinning plays an important role in plastic deformation of Mg alloys during low and medium temperature to accommodate the imposed strain, especially the strain along the c-axis. Therefore, the twinning behavior of AZ31 Mg alloy during plane strain compression at room temperature was investigated with EBSD in this work. Rectangular specimens with a dimension of 10 mm in length, 9 mm in width and 7 mm in thickness were cut from a hot rolled plate. The results show that {1012} twinning is dominant when the compression and constraint direction are parallel to transverse direction (TD) and rolling direction (RD) of the plate, respectively. The twinning variant selection mechanism is dominated by the Schmid factor (m) along compression direction, and also related to the constraint direction. The differences of twinning behavior can be interpreted by the twinning strain tensor. For the case when single twinning variant occurs within a grain, the average twinning strain tensor of twinning variant in constraint direction will result in spreading; while for the case there are two or more twinning variants taking place within a grain, the average twinning strain tensor of the variant with higher m will induce spreading in the constraint direction, and that with lower m results in size reducing in the constraint direction. During plane strain compression, different twinning variants coordinate with each other, twinning won' t be suppressed until the micro-strain in the constraint direction reaches 0.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Twinning induced plasticity (TWIP) steel exhibits high strength and exceptional plasticity due to the formation of extensive twin under mechanical load and its ultimate tensile strength and elongation to failure ductility-value can be as high as 5�104 MPa�%, which provide a new choice for automobile in developing the lightweight and improving safety. Generally, due to the texture was formed during process of plastic deformation, metal material appear anisotropic behavior. The deformation mechanisms, responsible for this high strain hardening, are related to the strain-induced microstructural changes, which was dominated by slip and twinning. Different deformation mechanisms, which can be activated at different stages of deformation, will strongly influence the stress strain response and the evolution of the microstructure. In this work, to predict the texture evolution under different loading conditions and understand these two deformation mechanisms of plastic deformation process, a polycrystal plasticity constitutive model of TWIP steel coupling slip and twinning was developed based on the crystal plasticity theory and single crystal plasticity constitutive model. A polycrystal homogenization method to keep geometry coordination and stress balance adjacent grains was used, which connected the state variables of single crystal and polycrystal. And then the model was implemented and programed based on the ABAQUS/UMAT platform. The texture evolution was obtained by EBSD at strain 0.27 and 0.60, respectively. The finite element models of tensile, compression and torsion processes were built by using the constitutive model. The mechanical response and texture evolution during plastic deformation process of TWIP steel were analyzed. The results show that with the increasing of the strain, the strain hardening phenomenon and texture density enhanced during the tensile process. Although texture types changed, texture density unchanged during the compression process. Owing to deformation increasing along the diameter direction, there is no obvious texture inside the cylinder when torsion deformation is small, texture emerged and enhanced gradually with the increasing of strain.
Subjects: Geosciences >> Other Disciplines of Geosciences submitted time 2019-09-10 Cooperative journals: 《干旱区研究》
Abstract：以白龙江流域石门乡至羊汤河段为例，采用松散物质面密度、地层岩性、构造断裂密度、地震密度、坡向、土壤可蚀性、土地利用类型、坡长坡度、沟床比降、流域沟壑密度及年均降雨量等11项评价因子的归一化值，在GIS平台下运用层次分析法建立泥石流易发性评价模型，将研究区泥石流易发性评价栅格图划分为4个等级。研究表明：泥石流中高易发区域占整个研究区面积的51.04%，区内发育的泥石流流域面积占中高易发区面积的68.71%，其分布特点具有沿大型活动性断裂呈带状分布，在次级断裂和小型褶皱密集区集中发育；沿易崩易滑地层呈片状展布，在沟壑密集带分区块集中发育；在坡面侵蚀强的区域多为泥石流高易发区，呈串珠状连片分布。利用研究区泥石流数据库对评价结果进行检验，检验曲线表明分区效果良好，检验曲线下面积即AUC值为62.13%，说明易发性评价结果较为可靠。
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-04 Cooperative journals: 《金属学报》
Abstract：基于晶体塑性理论，建立了滑移和孪生两机制耦合的孪生诱导塑性（TWIP）钢单晶晶体塑性本构模型，该模型通过引入孪晶体积分数及其饱和值，分别考虑了孪生对硬化及滑移的影响。对该本构模型数值实现，并在ABAQUS/UMAT平台上二次开发，将其应用于TWIP钢单晶典型取向单向加载条件下的力学行为模拟。分析了单晶不同取向下塑性变形的微观机理和滑移系、孪生系的启动状态及其对宏观塑性的影响。尤其是模拟得到了黄铜取向和S取向加载过程的应力突变，这再现了Cu单晶实验中的应力陡降现象。模拟结果表明：孪晶体积分数较小时，对应变硬化影响较小；随着孪晶体积分数的增加，对应变硬化的影响逐渐明显；当孪晶体积达到一定量时，孪晶体积达到饱和，孪生增量为0，晶体滑移转向，新的滑移系启动，应力突降。
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