一种半耦合韧性断裂准则及其在TRIP780中的应用

为研究高强钢板材在冷成形下的损伤演化与韧性断裂行为，将DF2012韧性断裂准则修正为初始损伤判据，同时参考连续损伤力学理论引入损伤变量D以衡量材料的累积损伤，并将其耦合到塑性模型中，构建了一种半耦合韧性断裂准则。以TRIP780高强钢板为研究对象，针对不同应力状态设计了6种形状的试样，借助电阻损伤测量法与DIC数字图像法进行了力学性能试验并测定初始损伤位移。采用非相关流动准则(NAFR)的Drucker各向异性屈服函数和Swift-Voce硬化模型准确描述了材料的塑性变形过程，然后分别利用试验模拟混合法和逆向工程法对初始损伤模型和损伤演化参数进行了标定。使用Fortran语言将构建的本构模型与损伤演化模型编译为VUMAT子程序并嵌入ABAQUS/Explicit模块中进行断裂模拟预测，并与未耦合损伤模型进行比较。结果表明：构建的半耦合韧性断裂准则能够准确描述TRIP780板材在不同应力状态下变形后期的损伤诱导软化行为，预测的断裂位移最大相对误差仅为1.31%。相较于常用的非耦合断裂模型，所提模型针对具有软化效应的高强钢表现出明显的优越性，适合用于高强钢板冷冲压成形的破裂预测中。

A semi-coupled ductile fracture criterion and its application on TRIP780high-strength steel sheet

To study the damage evolution and ductile fracture behavior of high-strength steel sheet under cold forming, we proposed a semi-coupled ductile fracture criterion. The DF2012 ductile fracture criterion was modified as the initial damage criterion. On the basis of the continuum damage mechanics (CDM) theory, the damage variable D was introduced to measure the cumulative damage of the material, and was coupled to the plasticity model. Taking TRIP780 high-strength steel as research object, six types of specimens were designed for different stress states. The resistance damage measurement and DIC digital image method were utilized to test the mechanical properties and initial damage displacement of specimens. The Drucker anisotropic yield function with non-associated flow rule (NAFR) and the Swift-Voce hardening model were used to accurately describe the plastic deformation process of the material. The initial damage model and the damage evolution parameters were calibrated by the hybrid test-simulation method and the inverse engineering method respectively. The constructed constitutive model and damage evolution model were compiled into the VUMAT subroutine using Fortran and implemented in the ABAQUS/Explicit module for fracture prediction, which were then compared with uncoupled damage model. Results show that the constructed semi-coupled ductile fracture criterion could accurately predict the damage-induced softening of TRIP780 sheets under different stress states. The maximum relative error of predicted damage displacement was only 1.31%. Compared with the commonly used uncoupled fracture model, the proposed model showed obvious superiority for high-strength steel with softening effect, which is suitable for fracture prediction in cold stamping forming of high-strength steel sheets.