Which one of the following graphs represents Griffith's criterion for the growth of a crack in a brittle isotropic infinitely large plate with a center crack? In the graph, ΔSE is the magnitude of the total strain energy released (shown by solid curve) and Γ_s is the total surface energy (shown by dashed line) and a_c is the critical crack length (shown by downward arrow) at which the crack starts growing. The tangent to the ΔSE curve parallel to the Γ_s line is shown by the dotted line.