Creep in Rock Salt

Abstract

The effects of temperature to 300° C, confining pressure to 1 kilobar, stress difference to 138 bars, and increased grain size on the creep behavior of rock salt were investigated. The creep tests were carried out on artificial polycrystalline rock-salt specimens and on one single crystal. An increase in either temperature or stress difference increases the creep rate considerably. An increase in confining pressure or grain size decreases the creep rate somewhat. The activation energy for creep in rock salt was found to range from 125,000 cal/mol at 29° C. to 30,000 cal/mol at 300° C. The creep curves of this work are well defined by the equation $$\epsilon = A + Bt^{n}$$, where $$\epsilon$$ is the deformation at a time t after application of load, and A, B, and n are constants with 0 < n < 1. A creep theory based on the intersection of moving dislocations and on dynamic recovery as creep-controlling mechanisms is considered.