  A continuum plasticity model for metals is presented from considerations of
non-equilibrium thermodynamics. Of specific interest is the application of a
fluctuation relation that subsumes the second law of thermodynamics en route to
deriving the evolution equations for the internal state variables. The modeling
itself is accomplished in a two-temperature framework that appears naturally by
considering the thermodynamic system to be composed of two weakly interacting
subsystems, viz. a kinetic vibrational subsystem corresponding to the atomic
lattice vibrations and a configurational subsystem of the slower degrees of
freedom describing the motion of defects in a plastically deforming metal. When
externally driven, the two subsystems, identified with their own temperatures,
fall out of equilibrium. An apparently physical nature of the present model
derives upon considering the dislocation density, which characterizes the
configurational subsystem, as a state variable. The continuum model
accommodates finite deformation and describes plastic deformation in a
yield-free setup via the so-called microscopic force balance along with the
more conventional macroscopic force balance. Though the theory here is
essentially limited to face-centered cubic metals modelled with a single
dislocation density as the internal variable, an extension to body-centered
cubic metals and modelling with two internal variables with dislocation
densities of two non-overlapping types are briefly touched upon.
