A rate‐ and state‐dependent ductile flow law of polycrystalline halite under large shear strain and implications for transition to brittle deformation

[1] We have conducted double‐shear biaxial deformation experiments in layers of NaCl within its fully‐plastic (FP) regime up to large shear strains (g < 50) with velocity steps. From this, we have empirically formulated a rate‐ and state‐dependent flow law which explains the transient mechanical behavior. The steady state flow stress in the FP regime can be explained by a power‐law with a stress exponent ∼8.5 and an activation enthalpy of ∼1.3 eV, with the instantaneous response having a higher stress exponent (13 ± 8), although there is data scatter. The transition to brittle regime is associated with weakening from the ductile flow law. In FP regime, the mechanical response is characterized by a monotonic decay to a new steady state while in the transitional regime, by a peak‐decay behavior. The transient flow law obtained here is of considerable importance in the study of the brittle‐ductile transition in rocks. Citation: Noda, H., and T. Shimamoto (2010), A rate‐ and state‐dependent ductile flow law of polycrystalline halite under large shear strain and implications for transition to brittle deformation, Geophys. Res. Lett., 37, L09310, doi:10.1029/2010GL042512.