  A new approach to defining the effective fracture toughness for heterogeneous
materials is proposed. This temporal averaging approach is process-dependent,
incorporating the crack velocity and material toughness. The effectiveness of
the new technique is investigated in the context of hydraulic fracture through
heterogeneous rock with a periodic material toughness. The plane strain model
is considered without fluid leak-off, to more easily investigate different
regimes (toughness/viscosity). Numerical simulations are used to examine the
effectiveness of the new homogenisation strategy, with comparison against the
recently-proposed maximum toughness strategy. Simulations are conducted using
an extremely effective (in house-built) time-space adaptive solver. The regimes
in which each strategy is effective are determined.
