  In this study, the phase field model of crack propagation is used to study
the dynamic branching instability in the case of inplane loading in two
dimensions. Simulation results are in good agreement with theoretical
predictions and experimental findings. Namely, the critical speed at which the
instability starts is about $0.48 c_s$. They also show that a full 3D approach
is needed to fully understand the branching instability. The finite interface
effects are found to be neglectable in the large system size limit even though
they are stronger than the one expected from a simple one dimensional
calculation.
