  Dislocations are the main carriers of plastic deformation in crystalline
materials. Physically based constitutive equations of crystal plasticity
typically incorporate dislocation mechanisms, using a dislocation density based
description of dislocation microstructure evolution and plastic flow.
Typically, such constitutive models are not formulated in a thermodynamic
framework. Nevertheless, fundamental considerations of thermodynamic
consistency impose constraints on the admissible range of model parameters
and/or on the range of application of such models. In particular, it is
mandatory to ensure that the internal energy increase associated with
dislocation accumulation is properly accounted for in the local energy balance.
We demonstrate on some examples taken from the literature how failure to do so
can lead to constitutive equations that violate the first and second laws of
thermodynamics either generally or in some particular limit cases, and we
discuss how to formulate constraints that recover thermodynamic consistency.
