The heterogeneous deformation of polycrystalline metals inherently originates from the intergranular deformation incompatibility. This paper proposes physical parameters related to the crystal orientations, the Schmid factor of the most activated slip system, and the misorientation angle to characterize the deformation incompatibility between the adjacent grain couple. A comprehensive multiscale investigation is conducted to reveal the mechanism from intergranular deformation incompatibility to fracture initiation at grain boundaries. At the specimen scale, experimental and numerical uniaxial tensile tests are performed on smooth and pre-notched dog-bone specimens to achieve different loading paths on the materials. The heterogeneous fields of stress triaxiality explains the heterogeneous size of the dimples observed in fractography. At the grain scale, electron backscatter diffraction analysis is conducted to characterize the microstructural properties around the nucleated voids within the materials. Voids are captured at the grain boundaries with directions parallel to the loading direction and intergranular deformation incompatibility is characterized using the proposed parameters. Simulations on the plastic deformation of realistic microstructures are performed to clarify the phenomenon. The results reveal that the fluctuation in stress triaxiality at grain boundaries is ascribed to intergranular deformation incompatibility, leading to fracture initiation at these sites. The relationships between the proposed physical parameters of intergranular deformation incompatibility and fluctuation in stress triaxiality are summarized in all circumstances. Finally, the ductile damage at the grain scale is predicted by the Rice–Tracey model, and the results show that the effects of microstructures on heterogeneous plastic deformation and stress state can be well considered.

中文翻译：

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晶间变形不相容对晶界应力状态和断裂萌生的影响：实验和晶体塑性模拟


多晶金属的异质变形本质上源于晶间变形的不相容性。本文提出了与晶体取向、最活跃滑移系的施密德因子以及取向差角相关的物理参数来表征相邻晶粒对之间的变形不相容性。进行了全面的多尺度研究，以揭示从晶间变形不相容到晶界处断裂萌生的机制。在样本尺度上，对光滑和预先切口的狗骨样本进行实验和数值单轴拉伸测试，以实现材料上的不同加载路径。应力三轴度的不均匀场解释了断口观察到的韧窝的不均匀尺寸。在晶粒尺度上，进行电子背散射衍射分析来表征材料内成核空隙周围的微观结构特性。在方向平行于加载方向的晶界处捕获空隙，并使用所提出的参数来表征晶间变形不兼容性。对现实微观结构的塑性变形进行模拟以阐明这种现象。结果表明，晶界处应力三轴度的波动归因于晶间变形不相容，导致这些部位发生断裂。总结了所有情况下所提出的晶间变形不相容物理参数与应力三轴度波动之间的关系。 最后，利用Rice-Tracey模型预测了晶粒尺度的延性损伤，结果表明可以很好地考虑微观结构对非均质塑性变形和应力状态的影响。