  Thermal fracture is prevalent in many engineering problems and is one of the
most devastating defects in metal additive manufacturing. Due to the
interactive underlying physics involved, the computational simulation of such a
process is challenging. In this work, we propose a thermo-mechanical
phase-field fracture model, which is based on a thermodynamically consistent
derivation. The influence of different coupling terms such as damage-informed
thermomechanics and heat conduction and temperature-dependent fracture
properties, as well as different phase-field fracture formulations, are
discussed. Finally, the model is implemented in the finite element method and
applied to simulate the hot cracking in additive manufacturing. Thereby not
only the thermal strain but also the solidification shrinkage are considered.
As for thermal history, various predicted thermal profiles, including
analytical solution and numerical thermal temperature profile around the
melting pool, are regarded, whereas the latter includes the influence of
different process parameters. The studies reveal that the solidification
shrinkage strain takes a dominant role in the formation of the circumferential
crack, while the temperature gradient is mostly responsible for the central
crack. Process parameter study demonstrates further that a higher laser power
and slower scanning speed are favorable for keyhole mode hot cracking while a
lower laser power and quicker scanning speed tend to form the conduction mode
cracking. The numerical predictions of the hot cracking patterns are in good
agreement with similar experimental observations, showing the capability of the
model for further studies.
