Abstract Accurately representing the process of porosity-based ductile damage in polycrystalline metallic materials via computational simulations remains a significant challenge. The heterogeneity of deformation in this class of materials due to the anisotropy of deformation of individual single crystals creates the conditions for the formation of a damage field. In this work, a technique of soft-coupled linkage between a macro-scale damage model and micro-mechanical calculations of a suite of polycrystal realizations of a representative BCC tantalum is presented. The macro-scale model, which accounts for rate-dependence and micro-inertial effects in the material, was used to represent two plate impact experiments and predict the point in time in the loading profile when porosity is initiated. The three-dimensional loading history from the macro-scale calculation was then used to define the probable loading history profile experienced within the samples. A micro-mechanical model based on an accurate representation of single crystal plasticity is then presented. Specifically, this model is employed in performing of polycrystal calculations of statistically representative microstructures of the tantalum material subjected to the extreme loading conditions informed from the macro-scale calculations. This enables to provide local-scale stress conditions for porosity initiation within the polycrystalline network. Furthermore, the micro-mechanical model captures the non-Schmid effects that accounts anomalous motion of the dominant screw dislocations within each of the single crystals. The results of the micro-mechanical simulations suggests that the non-Schmid effects significantly influence the local stress conditions across grain boundaries and triple junctions within the polycrystalline network. The computational results also suggest that the von Mises stress conditions and triaxiality at the grain boundaries and the grain boundary triple lines are highly variable but the variability is reduced with distance to the grain center. Furthermore, we found that the stress conditions at the grain boundaries are strongly dependent on the orientation of each boundary with respect to the shock direction.

中文翻译：

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动态加载过程中导致孔隙成核的局部微机械应力条件

摘要 通过计算模拟准确表示多晶金属材料中基于孔隙率的延性损伤过程仍然是一个重大挑战。由于单个单晶变形的各向异性，此类材料的变形不均匀性为损伤场的形成创造了条件。在这项工作中，提出了一种在宏观损伤模型和一组代表性 BCC 钽的多晶实现的微观机械计算之间的软耦合连接技术。宏观模型考虑了材料中的速率依赖性和微观惯性效应，用于表示两个板碰撞实验并预测孔隙率开始时加载曲线中的时间点。然后使用来自宏观计算的三维加载历史来定义样品中可能经历的加载历史曲线。然后提出了基于精确表示单晶塑性的微机械模型。具体而言，该模型用于对钽材料的统计上有代表性的微观结构进行多晶计算，这些微观结构受到宏观计算得出的极端负载条件的影响。这能够为多晶网络内的孔隙形成提供局部尺度的应力条件。此外，微机械模型捕获了非施密德效应，该效应解释了每个单晶内主要螺旋位错的异常运动。微机械模拟的结果表明，非施密德效应显着影响了多晶网络内晶界和三重结的局部应力条件。计算结果还表明，晶界和晶界三重线处的 von Mises 应力条件和三轴度变化很大，但随着距晶心距离的增加，变异性降低。此外，我们发现晶界处的应力条件强烈依赖于每个边界相对于冲击方向的取向。计算结果还表明，晶界和晶界三重线处的 von Mises 应力条件和三轴度变化很大，但随着距晶心距离的增加，变异性降低。此外，我们发现晶界处的应力条件强烈依赖于每个边界相对于冲击方向的取向。计算结果还表明，晶界和晶界三重线处的 von Mises 应力条件和三轴度变化很大，但随着距晶心距离的增加，变异性降低。此外，我们发现晶界处的应力条件强烈依赖于每个边界相对于冲击方向的取向。