A criterion for crack nucleation at a notch in homogeneous materials

Experiments of Parvizi et al. on transverse fracture of cross-ply laminates showed that both energy (Griffith) and strength criteria are necessary con ditions for fracture but neither one nor the other are sufficient. Thanks t o the singularity at the tip of the notch, the incremental form of the Grif fith criterion gives a lower bound of admissible crack lengths. On the cont rary, the strength criterion leads to an upper bound. The consistency betwe en these two conditions provides a general form of a criterion for crack nu cleation. (C) 2001 Academie des sciences/Editions scientifiques et medicale s Elsevier SAS.