Abstract A dual-scale finite element model is proposed to investigate the failure of ferrite-bainite (FB) dual-phase steel in the hole expansion test. The first level simulation solves the elastic-plastic deformation behavior with phenomenological isotropic elastic-anisotropic plastic constitutive models, and its resulting local deformation histories are supplied to the second level simulation as boundary conditions. In the second level simulation, the local microstructure evolution is solved and provides the dislocation densities, equivalent plastic strains, and stress triaxiality that measure the local fracture in grain scale. A special formulation for calculating the dislocation density distribution in the form of dislocation pile-up at grain boundary areas is highlighted as the microscale level constitutive law. The microstructural information is provided from image analyses based on grain average image quality (GavgIQ) and grain average misorientation (GAM) values observed using electron backscatter diffraction (EBSD). The data were used to identify the constituent phases of the FB steel as the major input for the microstructure-based representative volume element (RVE). Nanoindentation tests are employed to validate the identified phase and to extract the phase-level mechanical properties. The onset of failure at the hole edge during the hole expansion test is simulated by the proposed dual-scale numerical approach. Thus, both the hole expansion ratio (HER) and the location of failure can be successfully predicted. The example clarifies that the present approach based on local deformation histories and the resultant microstructure evolution with grain-level deformation inhomogeneity can be utilized for understanding the deformation and fracture of multi-phase steels.

中文翻译：

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铁素体-贝氏体钢扩孔失效预测性双尺度有限元模拟

摘要 为了研究铁素体-贝氏体(FB)双相钢在扩孔试验中的失效问题，提出了一种双尺度有限元模型。第一级模拟使用现象学各向同性弹-各向异性塑性本构模型求解弹塑性变形行为，并将其产生的局部变形历史作为边界条件提供给第二级模拟。在第二级模拟中，解决了局部微观结构演化，并提供了测量晶粒尺度局部断裂的位错密度、等效塑性应变和应力三轴度。用于计算晶界区域位错堆积形式的位错密度分布的特殊公式被强调为微尺度本构律。微观结构信息来自基于使用电子背散射衍射 (EBSD) 观察到的晶粒平均图像质量 (GavgIQ) 和晶粒平均取向差 (GAM) 值的图像分析。这些数据用于识别作为基于微观结构的代表性体积元素 (RVE) 的主要输入的 FB 钢的组成相。纳米压痕测试用于验证识别的相并提取相级机械性能。在扩孔试验期间孔边缘处的失效开始由所提出的双尺度数值方法模拟。因此，可以成功预测扩孔率 (HER) 和故障位置。