FRACTURE-BEHAVIOR OF FUSED QUARTZ WITH LASER-INDUCED INTERNAL FLAWS

Pulsed-laser light was used to generate internal flaws in fused quartz . The size of the flaw produced was proportional to the amount of lase r pulse energy above a threshold value of 2.5 mJ. Specimens of differe nt flaw sizes were tested at room temperature under four-point bending . The bending strength decreased as the flaw size increased, and a Gri ffith relationship was established between the lateral flaw size and t he critical stress at the flaw tip. Characteristic demarcation lines w ere observed on the fracture surfaces of specimens with a flaw size gr eater than 0.25 mm. It is suggested that the formation of the demarcat ion line is caused by a discontinuous change of stress intensity in th e dynamic process of the crack propagation.