Abstract In this study, the modified Mohr-Coulomb (MMC) ductile fracture criterion was employed to investigate the ductile fracture during the roll forming process of the AA6061-T6 aluminum alloy. To this aim, the MMC fracture criterion was calibrated based on the tension tests and was integrated into the commercial finite element (FE) Abaqus/Explicit using an appropriate user subroutine. The experimental procedures were designed based on two distinct forming strategies, namely single-stage and multi-stage roll forming processes. The results indicate that the calibrated fracture model based on tension tests is capable to predict the fracture initiation in the single-stage roll forming process at an error rate of 4.47%. Meanwhile, the numerically predicted fracture initiation during the multi-stage roll forming process is inconsistent with the experiments. Hence, a nonlinear damage accumulation rule together with the additional test (multi-stage L-bending) was utilized to predict the onset of fracture throughout the multi-stage roll forming process, considering the effect of deformation mechanics and nonlinear loading path during the process. The results reveal that the fracture onset during the multi-stage roll forming process can be accurately predicted when the MMC fracture criterion with the nonlinear damage accumulation rule is used in the numerical fracture model (with an error of about 9%).

中文翻译：

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U型槽型材滚轧成形中的延性损伤演化建模

摘要 本研究采用修正Mohr-Coulomb(MMC)韧性断裂准则研究AA6061-T6铝合金在滚压成形过程中的韧性断裂。为此，基于拉伸测试校准 MMC 断裂标准，并使用适当的用户子程序将其集成到商业有限元 (FE) Abaqus/Explicit 中。实验程序是基于两种不同的成型策略设计的，即单级和多级辊轧成型工艺。结果表明，基于拉伸试验的校准断裂模型能够以4.47%的误差率预测单级辊轧成形过程中的断裂起始。同时，多阶段辊轧成形过程中数值预测的断裂起始与实验不一致。因此，考虑到变形力学和非线性加载路径的影响，利用非线性损伤累积规则和附加试验（多级 L 弯曲）来预测整个多级辊轧成型过程中的断裂开始。 . 结果表明，在数值断裂模型中使用具有非线性损伤累积规则的MMC断裂准则可以准确预测多级辊轧成形过程中的断裂起始点（误差约为9%）。考虑到变形力学和非线性加载路径的影响，利用非线性损伤累积规则和附加测试（多级 L 弯曲）来预测整个多级辊轧成型过程中的断裂开始。结果表明，在数值断裂模型中使用具有非线性损伤累积规则的MMC断裂准则可以准确预测多级辊轧成形过程中的断裂起始点（误差约为9%）。考虑到变形力学和非线性加载路径的影响，利用非线性损伤累积规则和附加试验（多阶段 L 弯曲）来预测整个多阶段辊轧成型过程中的断裂开始。结果表明，在数值断裂模型中使用具有非线性损伤累积规则的MMC断裂准则可以准确预测多级辊轧成形过程中的断裂起始点（误差约为9%）。