Matrix crack deflection at an interface between a stiff matrix and a soft inclusion

Matrix crack deflection by an interface increases the apparent toughness of a composite. Criteria developed to predict such a mechanism never gave a c omplete and satisfying answer. They require additional assumptions on a cha racteristic fracture length and are sensitive to these choices. The criteri on proposed here is based on the maximum total energy decrease, it is indep endent of any length and is well-suited to study a stiff matrix crack impin ging on a soft inclusion. (C) 2000 Academie des sciences/Editions scientifi ques et medicales Elsevier SAS.