Anomalous plasticity in the cyclic torsion of micron scale metallic wires

Our new paper entitled "Anomalous
plasticity in the cyclic torsion of micron scale metallic wires" has been
accepted by PRL

(see: http://link.aps.org/doi/10.1103/PhysRevLett.110.244301)

The plasticity of micron-scale Cu and Au wires
under cyclic torsion is investigated for the first time using a torsion balance
technique. In addition to a size effect, a distinct Bauschinger effect and an
anomalous plastic recovery, wherein reverse plasticity even occurs upon unloading,
are unambiguously revealed. The Bauschinger effect and plastic recovery have
been observed in molecular dynamics and discrete dislocation dynamics
simulations of ideal single-crystal wires; the results here are an excellent
confirmation that these effects also occur in experiment in non-ideal polycrystalline
wires. A physical model consistent with the simulations is described in which
the geometrically necessary dislocations induced by the non-uniform deformation
in torsion play the key role in these anomalous plastic behaviors.

Firstly, this study has revealed, for the
first time, a series of anomalous plastic phenomena in the cyclic torsion of
micron-scale Cu and Au wires, including the size effect, distinct Bauschinger
effect, recoverable plasticity, different hardening behaviors between two
metals, etc. Each phenomenon may attract many attention. Secondly, these new
experiments provide an excellent confirmation of the previous molecular
dynamics and discrete dislocation dynamics simulations. These findings may have
significant implications in the basic mechanism for the cyclic plasticity at
small scales. Thirdly, these observations are physically explained by using the
dislocation theory. Especially, a physical model for the plastic recovery is
proposed. Two important conclusions are implied: (i) the geometrically
necessary dislocations contribute to the size effect in non-uniform
deformation, (ii) the geometrically necessary dislocations are another physical
origin of the Bauschinger effect and plastic recovery at small scales.