MOLECULAR DYNAMICS SIMULATION ON FRACTURE MECHANISMS OF NANO-SCALE POLYCRYSTAL UNDER STATIC AND CYCLIC LOADING

Abstract

The molecular dynamics simulation of fracture process under static and fatigue loading were done on a nano-scale polycrystal of pure iron, proposed in a previous paper. In the static tension, increasing tensile strain promoted the slip band formation near the grain boundary and finally resulted in microcrack initiation. Formation of subcracks and their growth along grain boundary layer dominated the fracture process at 100K. A large-scaled slip band formation along each grain boundary was observed in the simulation at 700K. The temperature-dependence of fracture process explained well the transition from the cleavage or brittle fracture to the ductile one. Regarding to the fatigue simulation, the fatigue life was decreased with increasing cyclic stress amplitude. At higher stress amplitude, many subcracks were simultaneously formed at the grain boundary and the final failure was dominated by the growth and coalescence of those subcracks. On the other hand, the fatigue fracture was controlled by the primary growth of a single crack formed among the subcracks at lower stress level.