ABSTRACT
Langer (1984) stated that reliable extrapolation of the creep equations at low deformation rates can be carried out only on the basis of deformation mechanisms. The micromechanisms that govern salt
1 INTRODUCTION
1.1 Norton-Hoff law
The mechanical behavior of salt has given rise to abundant literature. When a constant mechanical load is applied to a salt sample, most authors observe: a steady-state strain rate is reached after some time, it is a nonlinear function of the applied stress, it is sensitive to temperature, and no volume change is observed. The main features of such a steady-state behavior are captured by the NortonHoff law, or d dt Ass nε σp .( )Tσ , ( )Q RT Typical values for the constants n and Q/R range from 3 to 6 and from 3,000 to 10,000 K, respectively. The steady-state strain rate d dtε( ) is typically bout 10−10 s−1 for a deviatoric stress ( )σ of 10 MPa and temperature (T) of 300 K. This rate is relatively slow, and during most laboratory tests, the applied stress is larger than 10 MPa.
