Combined Method of Molecular Dynamics with Micromechanics in Simulations of Crack Propagation

抄録

Crack propagation and brittle fracture are simulated with a combined model of molecular dynamics with micromechanics. In the simulation of NaCl the material cleaves before it emits dislocations, whereas dislocation emissions are observed in experiments. In the simulations of tungsten we discuss the validity of interatomic potentials at first and simulate brittle fracture processes at the temperatures between 77 (K) and 225 (K). In the simulation using a pair potential, phase transformation, which is not likely to occur, is observed at the crack tip region, whereas it is not observed in the simulation using an EAM potential. In the simulation of brittle fracture processes using an EAM potential, cleavage along {121} planes is observed, while the pre-cracks are introduced on {110} planes. The cleavage along {121} planes is also observed in experiments. Fracture toughnesses obtained in the simulations show the clear temperature dependency. The values of fracture toughness, however, do not show good agreements with the experimental values. The critical stress intensity factor K_IE for dislocation emissions is discussed to investigate the thermal effect on the brittle fracture precesses. As the result, it is shown that the temperature dependency of fracture toughnesses are caused by the difference of dislocation mobilities.