  As shown by Wrobel et al. (2017), the hydraulically induced tangential
traction on fracture walls changes local displacement and stress fields. This
resulted in the formulation of a new hydraulic fracture (HF) propagation
condition based on the critical value of the energy release rate that accounts
for the hydraulically-induced shear stress. Therefore it is clear that the
crack direction criteria, which depend on the tip distributions of the stress
and strain fields, need to be changed. We analyse the two commonly used
criteria, one based on the maximum circumferential stress (MCS) and another -
on the minimum strain energy density (MSED). We show that the impact of the
hydraulically induced shear stress on the direction of the crack propagation is
negligible in the case of large material resistance to fracture, while for
small toughness the effect is significant. Moreover, values of the redirection
angles, corresponding to the so-called viscosity dominated regime, depend
dramatically on the ratios of the stress intensity factors.
