Observation of Fracture Features in Fused Quartz with Laser-Induced InternalFlaws

摘要

Pulsed-laser light was used to generate internal flaws in fused quartz. The sizeof the flaw was proportional to the laser pulse energy above a threshold value of 2.5 mJ. Specimens which fractured under four-point bending, either from surface origins or from the internal flaws with a size less than 0.25 mm, exhibited the commonly observed fracture features of sequential mirror, mist, hackle and branching, and the transition from the mirror to other features was gradual. However, in specimens with internal flaws of a size greater than 0.25 mm, a new 'demarcation' line (a smoothly curved boundary line between the mirror and other fracture features) was observed. Its characteristic varied with the flaw size and the relative position along the line. It is suggested that the formation of the demarcation line is caused by the combination of the dynamic process of crack propagation and environmental effects.