Molecular Dynamics Simulations of Orientation Effects During Tension, Compression, and Bending Deformations of Magnesium Nanocrystals

The deformation modes in magnesium nanocrystals during uniaxial tension, ta'tiarial compression, and pure bending are investigated using molecular dynamics (MD) simulations at room temperature. For each loading condition, the crystal orientation effects are studied by increasing the crystal c-axis orientation angle 0 relative to the loading direction from 0 deg to 90 deg by a 15 deg increment. The simulation results reveal a number of different deformation modes and an obvious tension compression asymmetry in magnesium nanocrystals. As the c-axis is rotated away from the tension loading direction, the deformation mode at yielding changes from tension twinning (theta <= 45 deg) to compression twinning (0 > 45 deg). For compression loading, yielding is dominated by only dislocation slip on the pyramidal (theta < 15 deg), basal (15 deg < theta < 60 deg) and prismatic (theta > 60 deg) planes. The nucleation stress in general decreases with increasing theta for both uniaxial tension and uniaxial compression loadings. For pure bending simulations, the yielding is mostly controlled by the weaker deformation mode between the compressive and tensile sides. The bending nucleation stress also decreases as the c-axis deviates away from the loading direction.