Abstract The mechanical response of hexagonal close-packed (HCP) materials are highly anisotropic due to the inherently asymmetric slip and twin systems in the HCP atomic structure. The slip and twin systems in the HCP atomic structure, i.e., slip/twin directions and planes, are not isotropic in terms of geometry. This inhomogeneous directionality produces various stress-strain responses along different loading directions. The question of which slip/twin systems are available in a specific HCP material has not been well understood and needs further experimental investigation. Since there was lack of experimental evidence that the pyramidal I slip is activated in single crystal magnesium, the pyramidal I slip has not been considered as the major slip mode in the computation research of single crystal magnesium. However, recent experimental and atomistic simulation works indicate that the pyramidal I slip is the dominant slip mode in the deformation of single crystal magnesium. Taking into account these recent findings on the pyramidal I slip in magnesium, this research aims to investigate the mechanical response of single crystal magnesium using the most number of slip/twin systems ever explored, including the pyramidal I slip system, tensile twin, compressive twin and etc. To quantify the contribution of each slip and twin system to overall deformation, i.e, the total shear strain amount, the plane strain compression experiment of single crystal magnesium performed by (Kelley and Hosford, 1967, 1968) is reproduced using crystal plasticity (CP) simulations. The computation scheme employed uses a standard crystal plasticity framework that takes into account the slip process and has an additional feature to implement the twinning process. Findings from the CP simulations indicate that the contribution of the pyramidal I slip mode to the overall shear strain in the deformation of single crystal magnesium is significant and comparable to that of the pyramidal II slip mode if their CRSS (Critical Resolved Shear Stress) are of similar magnitudes. The findings indicate as well that the pyramidal I slip mode will be dominant over pyramidal II in real experiments since the CRSS of pyramidal I has been reported to be smaller than that of pyramidal II by the recent experimental and atomistic simulation researches.

中文翻译：

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考虑滑移和孪晶的单晶镁力学响应研究

摘要 由于六方密堆积 (HCP) 材料的原子结构中固有的不对称滑移和孪晶系统，其机械响应具有高度的各向异性。HCP 原子结构中的滑移和孪晶系统，即滑移/孪晶方向和平面，在几何形状方面不是各向同性的。这种不均匀的方向性会沿着不同的加载方向产生各种应力应变响应。在特定的 HCP 材料中可用哪种滑动/孪生系统的问题尚未得到很好的理解，需要进一步的实验研究。由于缺乏单晶镁中锥体I滑移被激活的实验证据，因此在单晶镁的计算研究中，锥体I滑移并未被认为是主要的滑移模式。然而，最近的实验和原子模拟工作表明，金字塔 I 滑移是单晶镁变形的主要滑移模式。考虑到最近关于镁中锥体 I 滑移的这些发现，本研究旨在使用迄今为止探索的最多数量的滑移/孪晶系统来研究单晶镁的机械响应，包括锥体 I 滑移系统、拉伸孪晶、压缩孪晶为了量化每个滑移和孪晶系统对整体变形的贡献，即总剪切应变量，使用晶体塑性再现了 (Kelley and Hosford, 1967, 1968) 进行的单晶镁平面应变压缩实验(CP) 模拟。所采用的计算方案使用标准晶体塑性框架，该框架考虑了滑移过程并具有实现孪生过程的附加特征。CP 模拟的结果表明，如果它们的 CRSS（临界分辨剪切应力）为，金字塔 I 滑移模式对单晶镁变形中整体剪切应变的贡献是显着的，并且与金字塔 II 滑移模式的贡献相当相似的量级。研究结果还表明，由于最近的实验和原子模拟研究表明，金字塔 I 的 CRSS 小于金字塔 II 的 CRSS，因此在实际实验中，金字塔 I 滑移模式将优于金字塔 II。CP 模拟的结果表明，如果它们的 CRSS（临界分辨剪切应力）为，金字塔 I 滑移模式对单晶镁变形中整体剪切应变的贡献是显着的，并且与金字塔 II 滑动模式的贡献相当相似的量级。研究结果还表明，由于最近的实验和原子模拟研究表明，金字塔 I 的 CRSS 小于金字塔 II 的 CRSS，因此在实际实验中，金字塔 I 滑移模式将优于金字塔 II。CP 模拟的结果表明，如果它们的 CRSS（临界分辨剪切应力）为，金字塔 I 滑移模式对单晶镁变形中整体剪切应变的贡献是显着的，并且与金字塔 II 滑移模式的贡献相当相似的量级。研究结果还表明，由于最近的实验和原子模拟研究表明，金字塔 I 的 CRSS 小于金字塔 II 的 CRSS，因此在实际实验中，金字塔 I 滑移模式将优于金字塔 II。