Dislocation depinning transition in a dispersion-strengthened steel

Discrete dislocation dynamics simulations are used to investigate the dynamics of a driven dislocation line interacting with randomly distributed, incoherent oxide dispersoids that act as pinning centers in a bcc ferritic alloy. The dislocation line undergoes a depinning transition where the order parameter is the mean dislocation line velocity v, which increases in the depinning region from zero as v~(τ-τc)^β for external resolved shear stresses beyond a threshold value τc. The critical stress and critical exponents characterizing the depinning transition are determined numerically, and the observed dynamical behavior is compared with that of a depinning elastic string.