A coupled finite plasticity ductile damage and failure model is proposed for the finite element simulation of clinch joining, which incorporates stress-state dependency and regularisation by gradient-enhancement of the damage variable. Ductile damage is determined based on a failure indicator governed by a failure surface in stress space. The latter is exemplary chosen as a combination of the Hosford–Coulomb and Cockcroft–Latham–Oh failure criteria for the high and low stress triaxiality range, respectively, to cover the wide stress range encountered in forming. Damage is coupled to elasto-plasticity to capture the damage-induced degradation of the stiffness and flow stress. This affects the material behaviour up to failure, thereby realistically altering the stress state. Consequently, especially for highly ductile materials, where substantial necking and localisation precede material fracture, the failure prediction is enhanced. The resulting stress softening is regularised by gradient-enhancement to obtain mesh-objective results. The analysis of a modified punch test experiment emphasises how the damage-induced softening effect can strongly alter the actual stress state towards failure. Moreover, the impact of successful regularisation is shown, and the applicability of the damage and failure model to clinch joining is proven.

中文翻译：

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应力状态依赖性延性损伤建模，以铆接为例进行梯度增强


该文提出一种耦合的有限塑性延性损伤和失效模型，用于铆接的有限元模拟，该模型结合了应力-状态依赖性和通过损伤变量的梯度增强进行正则化。延性损伤是根据应力空间中的失效表面控制的失效指标确定的。后者是分别针对高应力和低应力三轴范围的 Hosford-Coulomb 和 Cockcroft-Latham-Oh 失效准则的组合而选择的典型例子，以涵盖成型中遇到的宽应力范围。损伤与弹塑性耦合，以捕获损伤引起的刚度和流动应力退化。这会影响材料的行为，直至失效，从而真实地改变应力状态。因此，特别是对于高延展性材料，在材料断裂之前会出现大量的颈缩和局部化，从而增强了失效预测。通过梯度增强对产生的应力软化进行正则化，以获得网格客观结果。对改进的冲头测试实验的分析强调了损伤诱导的软化效应如何强烈地改变实际的应力状态，使其趋向于失效。此外，还显示了成功正则化的影响，并证明了损伤和失效模型对铆接的适用性。