  We present a novel phase-field model development capability in the open
source MOOSE finite element framework. This facility is based on the 'modular
free energy' approach in which the phase-field equations are implemented in a
general form that is logically separated from model-specific data such as the
thermodynamic free energy density and mobility functions. Free energy terms
contributing to a phase-field model are abstracted into self-contained objects
that can be dynamically combined at simulation run time. Combining multiple
chemical and mechanical free energy contributions expedites the construction of
coupled phase-field, mechanics, and multiphase models. This approach allows
computational material scientists to focus on implementing new material models,
and to reuse existing solution algorithms and data processing routines. A key
new aspect of the rapid phase-field development approach that we discuss in
detail is the automatic symbolic differentiation capability. Automatic symbolic
differentiation is used to compute derivatives of the free energy density
functionals, and removes potential sources of human error while guaranteeing
that the nonlinear system Jacobians are accurately approximated. Through
just-in-time compilation, we greatly reduce the computational expense of
evaluating the differentiated expressions. The new capability is demonstrated
for a variety of representative applications.
