CONNECTING ATOMISTIC AND MESOSCALE SIMULATIONS OF CRYSTAL PLASTICITY

A quantitative description of plastic deformation in crystalline solid s requires a knowledge of how an assembly of dislocations-the defects responsible for crystal plasticity-evolves under stress(1). In this co ntext, molecular-dynamics simulations have been used to elucidate inte ratomic processes on microscopic (similar to 10(-10) m) scales(2), whe reas 'dislocation-dynamics' simulations have explored the long-range e lastic interactions between dislocations on mesoscopic (similar to 10( -6) m) scales(3). But a quantitative connection between interatomic pr ocesses and behaviour on mesoscopic scales has hitherto been lacking. Here we show how such a connection can be made using large-scale (100 million atoms) molecular-dynamics simulations to establish the local r ules for mesoscopic simulations of interacting dislocations. In our mo lecular-dynamics simulations,we observe directly the formation and sub sequent destruction of a junction (a Lomer-Cottrell lock) between two dislocations in the plastic zone near a crack tip: the formation of su ch junctions is an essential process in plastic deformation, as they a ct as an obstacle to dislocation motion. The force required to destroy this junction is then used to formulate the critical condition for ju nction destruction in a dislocation-dynamics simulation, the results o f which compare well with previous deformation experiments(4).