Abstract The application of ductile fracture criteria to shell elements yields invalid after the onset of necking and sensitivity to element size. The mesh-size regularisation strain study indicates that fracture strain modified with element dimension results in the same stress state. This phenomenon can't be accurately explained by current strain based fracture models. To fill this gap, this paper proposed that the fracture stress threshold σf for the Mohr-Coulomb criterion can be assumed to be an element dimension effect function of the form: σf (le) ∝ le-m. It follows then that the Modified Mohr-Coulomb fracture model and post-initiation damage are related to the element size by stress concentration exponent m. A plasticity and fracture testing program is performed on 1mm thick 301L steel sheets to test this hypothesis. The Arcan-type tests were employed to calibrate parameters for the damage initiation/fracture model in the equivalent plastic strain-stress triaxial space. The stress concentration exponent m was calibrated by a uniaxial tensile test by using different sizes of a virtual extensometer. At last, the model parameters are validated through a stretch bending test. The comparison of the experimental and FE simulation results demonstrates that the new coupled mesh size effect fracture model can predict stainless steel ductile fracture modelled by large sizes of shell elements with satisfactory accuracy.

中文翻译：

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用壳单元网格尺寸效应预测不锈钢板断裂

摘要 在颈缩开始和对单元尺寸敏感后，将延性断裂准则应用于壳单元屈服无效。网格尺寸正则化应变研究表明，用单元尺寸修改的断裂应变导致相同的应力状态。当前基于应变的断裂模型无法准确解释这种现象。为了填补这一空白，本文提出可以将 Mohr-Coulomb 准则的断裂应力阈值 σf 假定为以下形式的单元维数效应函数：σf (le) ∝ le-m。因此，修正的 Mohr-Coulomb 断裂模型和引发后损伤通过应力集中指数 m 与单元尺寸相关。对 1 毫米厚的 301L 钢板执行塑性和断裂测试程序以测试该假设。Arcan 型试验用于校准等效塑性应变-应力三轴空间中损伤起始/断裂模型的参数。应力集中指数 m 是通过使用不同尺寸的虚拟引伸计通过单轴拉伸试验校准的。最后通过拉伸弯曲试验对模型参数进行验证。实验和有限元模拟结果的比较表明，新的耦合网格尺寸效应断裂模型可以以令人满意的精度预测由大尺寸壳单元建模的不锈钢韧性断裂。应力集中指数 m 是通过使用不同尺寸的虚拟引伸计通过单轴拉伸试验校准的。最后通过拉伸弯曲试验对模型参数进行验证。实验和有限元模拟结果的比较表明，新的耦合网格尺寸效应断裂模型可以以令人满意的精度预测由大尺寸壳单元建模的不锈钢韧性断裂。应力集中指数 m 是通过使用不同尺寸的虚拟引伸计通过单轴拉伸试验校准的。最后通过拉伸弯曲试验对模型参数进行验证。实验和有限元模拟结果的比较表明，新的耦合网格尺寸效应断裂模型可以以令人满意的精度预测由大尺寸壳单元建模的不锈钢韧性断裂。