It is worthy to investigate how it will affect the parameters calibration using an average stress state variable before the practical application of a ductile fracture criterion. In order to study this problem, ten notch specimens of AA7075-T6 sheet were designed to implement the tension tests and a parallel simulation of each test was run to obtain the variation of related variables such as stress triaxiality, Lode parameter and fracture strain. The Lou-Huh criterion was selected to research the prediction error through the difference between the damage value calculated by integral expression and that calculated by analytical expression. Based on the error analysis method, a clear answer was given on how to choose the tension tests of notch specimens in the calibrating process of fracture parameters. The studying results show that the stress state variation of notch specimens has a significant influence on the calibration result. It turns out that how to choose specimens from the ten notch specimens to calibrate the fracture parameters also has big influence on the result. Therefore, it is necessary to conduct an error analysis after the calibration of fracture parameters. Based on the error analysis results, the fracture parameters of AA7075-T6 sheet were optimized and its forming limit diagram (FLD) was deduced based on the optimized parameters. The predictive result of FLD is safe compared with the experimental forming limit results.

值得一提的是，在实际应用延性断裂准则之前，使用平均应力状态变量来研究它将如何影响参数校准。为了研究该问题，设计了十个AA7075-T6板材的缺口试样以进行拉伸试验，并对每个试验进行并行模拟，以获得相关变量的变化，例如应力三轴性，Lode参数和断裂应变。选择Lou-Huh准则，通过积分表达式计算出的损伤值与解析表达式计算出的损伤值之间的差来研究预测误差。基于误差分析方法，给出了在裂缝参数校准过程中如何选择缺口试样拉伸试验的明确答案。研究结果表明，缺口试样的应力状态变化对标定结果有很大影响。事实证明，如何从十个缺口试样中选择试样来校准断裂参数，对结果也有很大的影响。因此，有必要在断裂参数校准后进行误差分析。根据误差分析结果，优化了AA7075-T6板材的断裂参数，并根据优化参数推导了其成形极限图（FLD）。与实验成形极限结果相比，FLD的预测结果是安全的。事实证明，如何从十个缺口试样中选择试样来校准断裂参数，对结果也有很大的影响。因此，有必要在断裂参数校准后进行误差分析。根据误差分析结果，优化了AA7075-T6板材的断裂参数，并根据优化参数推导了其成形极限图（FLD）。与实验成形极限结果相比，FLD的预测结果是安全的。事实证明，如何从十个缺口试样中选择试样来校准断裂参数，对结果也有很大的影响。因此，有必要在断裂参数校准后进行误差分析。根据误差分析结果，对AA7075-T6板材的断裂参数进行优化，并根据优化参数推导其成形极限图（FLD）。与实验成形极限结果相比，FLD的预测结果是安全的。