Molecular dynamics study for low temperature brittleness in a tungsten single crystal

A combined model of molecular dynamics with micromechanics was applied to simulations for low temperature brittleness in a tungsten single crystal. Temperature dependency of fracture toughness in low temperature was a main subject in this research. Fracture toughnesses at 77∼225 K were evaluated in simulations. Evaluated toughnesses showed clear temperature dependency, although there were differences between simulation results and experimental results. Two local stresses in nano-scale at a crack tip were introduced to explain a brittle fracture process. One was a driving force for slip and the other for cleavage. The driving force for cleavage was gradually increased after emissions of dislocations although driving force for slip was saturated, and cleavage was caused by the increased driving force when it reached a critical value. The critical values of the driving forces were not influenced by temperature. It meant that emissions of dislocations was not influenced by temperature but mobility of dislocations controlled the temperature dependency of fracture toughness.