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 complete and satisfying answer. They require additional assumptions on a characteristic fracture length and are sensitive to these choices. The criterion proposed here is based on the maximum total energy decrease, it is independent of any length and is well-suited to study a stiff matrix crack impinging on a soft inclusion.