Molecular dynamics study on low temperature brittleness in tungsten singlecrystals

This study employed a numerical model combining molecular dynamics and micr omechanics to study the low temperature fracture of tungsten. In the simula tions a pre-crack was introduced on the (110) planes and cleavage was obser ved along the (121) planes. Cleavage along (121) planes has also been obser ved in experiments. Simulations were performed with three sizes of molecula r dynamic regions at 77 K, and it was found that the results were independe nt of the size. Brittle fracture processes were simulated at temperatures b etween 77 K and 225 K with the combined model. The fracture toughness obtai ned in the simulations showed clear temperature dependency, although the va lues showed poor agreement with experimental results. A brittle fracture pr ocess at 77 K was discussed considering driving forces for dislocation emis sions and cleavage in an atomic scale region of the crack tip. The driving force for dislocation emissions was saturated after the first dislocation e mission, whilst the driving force for cleavage gradually increased with the loading K-field. The increased driving force caused cleavage when it reach ed a critical value. The critical values of driving force, which were close to the theoretical strength of the materials, were not influenced by tempe rature. This indicates that the temperature dependency of fracture toughnes s is not caused by the temperature dependency of dislocation emissions; but by that of dislocation mobility.