Atomistic simulations for the evolution of a U-shaped dislocation in fcc Al

Through massively parallel molecular dynamics simulations for the evolution of U-shaped dislocation in face-centered cubic aluminum, conventional and noncoplanar (in a helical form) evolutions of dislocation segments are revealed at the atomistic scale. The two different evolutions are closely related to the Frank-Read multiplication mechanism. The possibility of noncoplanar process is quantitatively analyzed using a combination of continuum dislocation dynamics theory and atomistic simulations. The cross-slip mechanism involving in the noncoplanar evolution is supported by examining its energy barrier and critical stress. It is suggested that the operations of two different evolutions are dictated by the strain rate and the crystal size.