  We present a simple and robust implementation of the phase field fracture
method in Abaqus. Unlike previous works, only a user material (UMAT) subroutine
is used. This is achieved by exploiting the analogy between the phase field
balance equation and heat transfer, which avoids the need for a user element
mesh and enables taking advantage of Abaqus' in-built features. A unified
theoretical framework and its implementation are presented, suitable for any
arbitrary choice of crack density function and fracture driving force.
Specifically, the framework is exemplified with the so-called AT1, AT2 and
phase field-cohesive zone models (PF-CZM). Both staggered and monolithic
solution schemes are handled. We demonstrate the potential and robustness of
this new implementation by addressing several paradigmatic 2D and 3D boundary
value problems. The numerical examples show how the current implementation can
be used to reproduce numerical and experimental results from the literature,
and efficiently capture advanced features such as complex crack trajectories,
crack nucleation from arbitrary sites and contact problems. The code developed
can be downloaded from www.empaneda.com/codes.
