Crack-Front Curvature and Glass Slow Fracture

Fracture-surface markings on glass samples broken under liquid decane indicate that region II constitutes a transition between environmentally assisted and environmentally free fracture modes. Region II itself is subdivided into two stages, both characterized by negative crack-front curvature. This reversed curvature develops initially to allow more time for diffusion of the environmental agent to the middle portion of the fracture front and leads to increased local stress which activates the environmentally independent fracture mode at the center of the fracture front. Most of region II occurs in the latter mixed-mode fracture condition.