  Intermittent plastic deformation in crystals with power-law behaviors has
been reported in previous experimental studies. The power-law behavior is
reminiscent of self-organized criticality, and mesoscopic models have been
proposed that describe this behavior in crystals. In this letter, we show that
intermittent plasticity in metals under tensile deformation can be observed in
molecular dynamics models, using embedded atom method potentials for Ni, Cu,
and Al. Power-law behaviors of stress drop and waiting time of plastic
deformation events are observed. It is shown that power-law behavior is due to
dislocation avalanche motions in Cu and Ni. A different mechanism of
dislocation pinning is found in Al. These different stress relaxation
mechanisms give different power-law exponents. We propose a probabilistic model
to describe the novel dislocation motion in Al, and analytically deduce the
power-law behavior.
