Behaviour of slow-propagation cracks in quartz glass

Abstract

The behaviour of slow-propagation cracks in quartz glass has been studied experimentally by the technique of acoustic emission combined with fracture mechanics at room temperature and in moistened air. As the stress intensity factor K 1 is lower than the critical stress intensity factor K 1c, the double torsion technique was used to measure the crack propagation velocity, d a/d t, and the acoustic emission rate d N/d t simultaneously. The experimental results show that the relationship between In( da dt ) or In( da dt ) and K 13is linear, when K 1 is within the range studied. [At the same time, a linear relationship exists between In( da dt ) and In( da dt ) .] The results obtained in a moistened atmosphere show that under the same load (same stress intensity factor), the crack velocity is markedly increased with the presence of water vapor, yet the acoustic emission rate increases slowly. It was concluded that by measuring the crack propagation by the acoustic emission technique and using the fracture mechanics calculation, the service life of the quartz glass structure parts may be predicted.