Rheology of synthetic polycrystalline halite in torsion

Motivated by the need for halite rheology, we investigated the stress/strain/strain rate behaviour of halite to high shear strains in torsion, using polymer jackets whose strength does not influence halite rheology. The experimental results show that: (1) halite strength decays exponentially with temperature increase, being very weak at 300 degrees C (ca. 2 Nm); (2) power-laws fit the stress/strain rate data, from which we determined the stress exponent n between ca. 13 (60 degrees C) and ca. 3 (200 degrees C), indicating that n decreases exponentially with temperature increase; (3) the activation energy Q decreases exponentially with temperature increase, from ca. 159 kJ/mol (38 kcal/mol) at 60 degrees C to ca. 59 kJ/mol (14 kcal/mol) at 200 degrees C; (4) Q depends linearly on n with a slope of ca. 10. The empirical constitutive equation (gamma) over dot = 12.1exp(9.6 + 7.1E-6exp(1/T1.9E-4))tau((25+93E6exp(-T/24 3))) describes the experimental results. Comparison of the present and previous experimental results shows that halite is much weaker in shear than in axial compression or extension. This difference likely results from the rotational component of simple shear. (C) 2012 Elsevier B.V. All rights reserved.