  The homogenisation of the fracture toughness is considered in the context of
a propagating hydraulic fracture. The radial (penny-shape) model is utilized,
in order to incorporate the impact of the viscosity-toughness regime transition
over time. A homogenisation strategy based upon temporal-averaging is
investigated. This approach incorporates the instantaneous fracture velocity,
meaning that it should remain effective in the case of step-wise crack
advancement. The effectiveness of the approach is demonstrated for periodic
toughness distributions, including those which are unbalanced, utilizing a
highly accurate solver.
