耦合孪生的TWIP钢单晶体塑性变形行为模拟研究

MODELLING OF PLASTIC DEFORMATION ON COUPLING TWINNING OF SINGLE CRYSTAL TWIP STEEL

基于晶体塑性理论,建立了滑移和孪生机制耦合的孪生诱导塑性(TWIP)钢单晶晶体塑性本构模型,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,对该本构模型进行数值实现.并通过ABAQUS/UMAT平台上的二次开发,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,尤其是模拟得到黄Cu取向和S取向加载过程的应力突变,再现了Cu单晶实验中的应力陡降现象.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.

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 crystalplasticity 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.