Competition between plasticity- and void-based dynamic damage behaviors of single crystal HCP-Zr by considering the high strain rate and temperature

Abstract

Spall dynamic damage has been extensively investigated in ductile metals with weak mechanical anisotropies, such as copper, iron, and aluminum. However, the fracture of stronger anisotropic metals, especially those with HCP structures, remains far less understood. In this work, the void evolution, including nucleation, growth, and coalescence, in single crystal HCP-zirconium at triaxial ultra-strain rates was investigated using molecular dynamics modeling. The internal pressure, microstructural evolution, and void evolution dynamics under various strain rates and temperatures were examined to reveal two competitive mechanisms, i.e., the competition between the dislocation and void evolution and the competition between the structural phase transformation and void evolution. The results showed that at the initial stage of void nucleation, the dislocations and voids exhibited interacted. However, when voids began to grow exponentially, they moved toward the dense dislocation direction and reduced the space for dislocation growth. In addition, the change in the pressure peak was caused by the sequence between the structural phase transformation and void nucleation under the strain rate strengthening effect and temperature softening action. When the void creation was ahead of the structural phase transformation, the pressure dropped once with only one peak. Contrarily, when the void nucleation lagged behind the structural phase transformation, two peaks appeared in the pressure–strain profile. The findings of this study are expected to be useful for the development of a fracture model that accounts for the effects of high strain rates and temperatures on the dynamic damage behavior across multiple scales.