  We introduce a new phase-field model which allows for simulation of
incoherent solid/solid transformations. Contrary to previous models which
impose coherency at the interface, the zero shear-stress condition
characteristic of incoherent solids is recovered in the limit of small
interface thickness. For the sake of clarity, we limit ourselves to the case of
stress-driven phase transitions between two elastic solids. However, since we
use a variational formulation which has a clear thermodynamic interpretation,
the extension of the model to the cases of chemical and/or thermal diffusion is
straightforward.
