Time-dependent crack growth in quartz and its application to the creep of rocks

Abstract

The time-dependent growth of an axial crack in single-crystal quartz tested in uniaxial compression with a constant load was studied as a function of temperature, T stress σ and partial pressure of water P. The time-dependent growth can be approximated by an equation of the form C − C0 = Atn, where C is crack length. Typically, as any one of the three variables was increased, the rate of crack growth increased. The data were analyzed by comparing the relative times required for two cracks, with the same initial length, to extend an arbitrarily selected increment of 0.20 mm as one of the parameters was varied. The experimental results indicate that the changes in the rate of crack growth due to a variation in any of three variables could be treated independently over the range studied and expressed by where t1 and t2 are the times required for a crack to extend 0.20 mm. The relation between environment-sensitive time-dependent crack growth and creep in brittle rocks is discussed. The increase in the rate of creep strain in rocks due to an increase in temperature or stress is consistent with the explanation of creep in terms of crack growth. The static fatigue of glasses, brittle rocks, and quartz is shown to obey a dependence on stress, temperature, and moisture similar to the time-dependent crack growth in quartz.