Accurately obtaining the material parameters of the damage model is very important for the ductile fracture simulation of steel structures made of high strength steel (HSS). The combination of micromechanics with the uncoupled phenomenological fracture model can be used to obtain the material parameters of ductile fracture locus only from the uniaxial engineering stress-strain relationship. A micro failure index is generally used to link the material fracture under different multiaxial stress status. It is relatively difficult to describe the irregular micro-void evolution using the microvoid radius, and also difficult to tackle the micro void coalescence of the mesoscale using microvoid volume fraction. The mesoscale critical equivalent plastic strain (MCEPS) is proposed as the failure index at the unit cell level to calibrate the fracture locus of the uncoupled phenomenological model in this paper. The fracture locus of the HSS is calibrated by comparing the FE results with experimental data using the homogenized MCEPS and maximum MCEPS at the microvoid surface, respectively. The identified fracture locus is further validated against five stress status, including butterfly shear specimen, butterfly tension specimen, the tensile specimen with the symmetric round notch, tension specimen with a central hole in the middle, and Sandia fracture challenge specimens in 2014. The comparisons of predictions with the experimental results showed that the proposed MCEPS index can be used to obtain the material parameters of the ductile fracture locus.

准确获取损伤模型的材料参数对于由高强度钢（HSS）制成的钢结构的延性断裂模拟非常重要。微观力学与非耦合现象学断裂模型的结合可以仅从单轴工程应力-应变关系中获得延性断裂轨迹的材料参数。通常使用微破坏指数来链接在不同多轴应力状态下的材料断裂。用微孔半径描述不规则的微孔演化是相对困难的，并且使用微孔体积分数很难解决中尺度的微孔聚结。本文提出了中尺度的临界当量塑性应变（MCEPS）作为单位单元水平的失效指标，以校正非耦合现象学模型的断裂轨迹。通过分别在微孔表面均质化的MCEPS和最大MCEPS将FE结果与实验数据进行比较，来校准HSS的断裂轨迹。在2014年，针对五个应力状态进一步验证了所识别的断裂轨迹，包括蝶形剪切试样，蝶形拉伸试样，具有对称圆形缺口的拉伸试样，中间带有中心孔的拉伸试样以及Sandia断裂挑战试样。实验结果的预测结果表明，所提出的MCEPS指数可用于获得韧性断裂轨迹的材料参数。