2016 年 65 巻 2 号 p. 141-147
Crack propagation in Magnesium was investigated using molecular dynamics (MD) simulations. By using a disk-shaped atomic cell containing a crack under the anisotropic linear elastic displacement, the deformation field around the crack tip was first atomistically resolved. In order to consider effects of surface energy on crack propagation, two kinds of interatomic potentials were adopted. For an embedded atom method (EAM) potential, basal and first-pyramidal surfaces are favorable cleavage planes due to relatively low surface energies. Thus, MD simulations using the EAM showed unstable crack propagation on those planes. For the other generalized embedded atom method (GEAM) potential which provides the higher surface energies instead, the basal plane has the larger critical stress intensity factor by the Griffith’s formula because it is proportional to square root of surface energy. Consequently, the dislocation nucleation and deformation twin nucleation were occurred in the vicinity of the crack tip. The other MD analyses of defect interaction between a crack and twin boundaries (TBs) were also carried out. Twinning dislocations of (1012) twin were generated by reaction with the basal dislocations emitted from the crack tip, and thus (1012) TB easily moved. On the other hand, a void or deformation twin was generated along the boundary region where the dislocations from the crack tip piled up, and then the crack propagation near (1011) TB arose.