Texture, microstructure, and local grain neighbourhood contribute to the development of localized stresses in polycrystals. For hexagonal close-packed materials, crystal's elastic and plastic anisotropy can also be a major contributing factor, yet there is a paucity of experimental studies focusing on the extent of contribution of such parameters on the magnitude of localized stresses at microscales. This study focuses on addressing this knowledge gap by deforming double-edge-notched soft-textured α-zirconium specimens in-situ, while measuring grain scale tensorial stresses using high energy synchrotron X-ray diffraction. The specimens were subjected to cyclic loads to study the evolution of stresses in the vicinity of both shallow and deep notches. The soft-texture of the specimens is such that there are no c-axes of grains aligned along the macroscopic loading direction thereby inhibiting deformation twinning. The “as-measured” microstructures and notch geometries were imported into a crystal plasticity finite element model for further analysis. Results show that despite the absence of c-axes of grains aligned along loading direction, the developed stresses were substantially influenced by crystallographic orientations. Stress drop was observed near the onset of plasticity with further loading and the orientation and position effects were highlighted. A plastic deformation mechanism was revealed where, upon specimen loading, the mechanical constraints enforced during grain-grain interactions led to hardening. Accordingly, a parameter was devised to quantify the grain level hardening arising from this mechanism. It was shown that grain-scale stress concentration factors vary significantly before the onset of plasticity, but they settle in the plastic zone and with the progression of cycles.

中文翻译：

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软织构锆多晶中缺口尖端周围晶粒分辨应力场的发展：三维同步加速器 X 射线衍射研究


织构、微观结构和局部晶粒邻域有助于多晶中局部应力的发展。对于六方密堆积材料，晶体的弹性和塑性各向异性也可能是一个主要影响因素，但很少有实验研究关注这些参数对微尺度局部应力大小的贡献程度。本研究的重点是通过原位变形双刃缺口软纹理 α-锆样品来解决这一知识差距，同时使用高能同步加速器 X 射线衍射测量晶粒尺度张应力。使样本承受循环载荷，以研究浅凹口和深凹口附近的应力演变。样品的质地较软，没有沿宏观加载方向排列的晶粒 c 轴，从而抑制了变形孪晶。将“测量的”微观结构和凹口几何形状导入晶体塑性有限元模型中以进行进一步分析。结果表明，尽管不存在沿加载方向排列的晶粒 c 轴，但产生的应力很大程度上受到晶体取向的影响。随着进一步加载，在塑性开始附近观察到应力下降，并且突出了方向和位置效应。揭示了塑性变形机制，在样品加载时，晶粒相互作用期间施加的机械约束导致硬化。因此，设计了一个参数来量化由该机制引起的晶粒级硬化。 结果表明，晶粒尺度应力集中因子在塑性开始之前变化很大，但它们在塑性区域内并随着循环的进行而稳定下来。