MOLECULAR-DYNAMICS STUDY OF CRACK PROCESSES ASSOCIATED WITH DISLOCATION NUCLEATED AT THE TIP

Atomic scale changes of structure around a crack-tip in an f.c.c. crys tal under in-plane shear (mode II) loading are analyzed by molecular d ynamics simulation (MD simulation), and its counterpart in the continu um crystal plasticity model is discussed. A ductile fracture process i nvolving dislocation nucleation from the stressed tip is always observ ed. The nucleated dislocation is driven away from the crack and a disl ocation-free zone develops in the near-tip region. Time averages of lo cal stress in the near-tip region, both before and after dislocation n ucleation, coincide well with the linear elastic prediction. The criti cal stress intensity factor estimated by MD simulation agrees well wit h Rice's theoretical prediction derived from the unstable stacking ene rgy concept. The temperature dependence of the critical factor can be explained primarily as a thermally activated process.