Molecular dynamics simulation on the cyclic deformation of magnesium single crystals

ZY Xing and HD Fan and J Tang and B Wang and GZ Kang, COMPUTATIONAL MATERIALS SCIENCE, 186, 110003 (2021).

DOI: 10.1016/j.commatsci.2020.110003

Molecular dynamics simulations were performed to investigate the cyclic deformation of magnesium single crystalline nano-pillars in the first three cycles. To study the tension-compression asymmetry, two symmetric uniaxial cyclic loading paths (applied strain amplitude = 10%) were employed, i.e., a triangle wave loading path started by tension and a triangle wave loading one started by compression. The influence of crystalline orientation on the cyclic deformation of magnesium nano- pillars was studied by changing the angle theta between the loading direction and the c-axis of the nano-pillars (e.g., 0 degrees, 45 degrees, and 90 degrees). Under the cyclic loading path started by tension, the full deformation process in each cycle is controlled by twinningdetwinning-pyramidal slip-retwinning at theta = 0 degrees with significant tension-compression asymmetry observed, basal slip + twinningdetwinning-basal slip + retwinning at theta = 45 degrees without any tension-compression asymmetry, and double twinning-detwinning- retwinning-detwinning at theta = 90 degrees with significant tension- compression asymmetry. Under the cyclic loading one started by compression, on the other hand, the deformation process is dominated by pyramidal slip-twinning-detwinning at theta = 0 degrees, basal slip- twinning-detwinning-retwinning at theta = 45 degrees, and prismatic slip-double twinning-detwinning in the first two cycles and twinning- detwinning-retwinning in the third cycle at theta = 90 degrees, while tension-compression asymmetry is observed in the cases at theta = 0 degrees and 90 degrees only due to different deformation modes in the tension and compression stages. Especially, for the loading path started by compression at theta = 90 degrees, cyclic hardening is seen in the tension stage, but softening is observed in the compression stage only in the third cycle due to the change of deformation modes. The current work provides new insights for understanding the mechanical property of Mg crystals subjected to a cyclic loading.

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