Influence of internal stresses on the development of cracks in glasses

Fracture phenomena due to internal stresses in toughened glass plates are described. Compared with uniform stress fields a different crack propagation and branching behaviour is observed which can be explained formally by an effective crack length of the order of the plate tickness. The influence of internal stresses on the crack front curvature is shown and a method to measure the K-distribution along the crack front is proposed.