G 1 NR = 1 Δ Δ a F 2 Δ Δ u 2 2 G 2 NR = 1 Δ Δ a F 1 Δ Δ u 1 2 G 3 NR = 1 Δ Δ a F 3 Δ Δ u 3 2 Where Δ Δ a is the width of the element bounding the crack tip. The accuracy of the method highly depends on the mesh refinement, both because the displacement and forces depend on it, and because G = lim Δ Δ a → → 0 G NR . Note that the equations above are derived using the crack closure integral.