Shear deformation is one of the primary factors determining the threshold of structural transition (ST). It is important to quantitatively express the relationship between shear deformation and the ST threshold for the in-depth development of ST dynamics models. This work used classical molecular dynamics methods to study the effect of shear deformation on the ST in iron by controlling the triaxial ratio of compression. Based on the simulation results, there are significant differences in the microstructure for different loading paths. HCP lamellar twins, HCP-FCC thin twins, and crossed HCP twins embedded with parallel hexahedral FCC grains were all observed, as uniaxial loading transitions to equiaxial loading. The changes in pressure and the softening range of shear stress under different triaxial compressions were revealed. By introducing the strain triaxiality (i.e., the ratio of shear strain to volumetric strain), a general expression of the pressure threshold of ST under high strain rate compression-shear was proposed. In addition, whether the close-packed plane is easily activated under different strain environments was explained based on the results of stacking fault energy.

中文翻译：

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任意三轴压缩下 BCC 铁中 HCP/FCC 成核的阈值和结构：原子模拟

剪切变形是决定结构转变（ST）阈值的主要因素之一。定量表达剪切变形与ST阈值之间的关系对于ST动力学模型的深入发展具有重要意义。该工作采用经典分子动力学方法，通过控制压缩三轴比来研究剪切变形对铁中ST的影响。根据模拟结果，不同加载路径的微观结构存在显着差异。当单轴载荷转变为等轴载荷时，均观察到了 HCP 层状孪晶、HCP-FCC 薄孪晶以及嵌入平行六面体 FCC 晶粒的交叉 HCP 孪晶。揭示了不同三轴压缩下压力的变化和剪切应力的软化范围。通过引入应变三轴性（即剪切应变与体积应变之比），提出了高应变率压剪下ST压力阈值的通用表达式。此外，根据堆垛层错能的结果解释了密排平面在不同应变环境下是否容易被激活。