Sub-critical Crack Propagation in Glass in Reservoir Conditions

Abstract

The presented work takes place in the context of the storage of vitrified radioactive wastes. The mechanical behavior of crack in glass under pressure at low strain rate is of great interest. The present work is focused on the time dependency of crack propagation in glass. Experiments are performed in triaxial conditions on thermally cracked boro-silicate glass samples. The initial crack network is introduced through a thermal shock (the sample is slowly heated up to 300°C and then it is quenched into water at ambient temperature). The creep tests are performed by increasing the axial stress step by step (at constant confining pressure, temperature and pore fluid pressure). Results show that during creep tests, dilatancy is observed. This is not the case for regular triaxial test. The dilatancy is correlated to a non-zero acoustic emission rate that is evidenced by the sub-critical crack propagation. This crack growth induced localized failures. In addition, increasing temperature increases the strain rate and reduces the time to rupture. The different experiments performed at different temperatures allow to determine the activation energy (32 KJ/mol). The effect of confining pressure and differential stress is also investigated in order to extrapolate to long time scales, as in storage conditions.