The role of damage and recrystallization in the elastic properties of columnar ice

Effects of damage on elastic properties were studied in columnar-grained specimens of freshwater and saline ice, subjected, at -10 degrees C, to varying levels of inelastic strain. The ice was compressed uniaxially at constant strain rates up to 0.20 strain, which caused localized recrystallization and imparted damage in the form of non-propagating cracks. Damage was quantified in terms of dimensionless crack density, which, along with recrystallized area fraction, was determined from thin sections. The change in porosity due to stress-induced cracks served as another indicator of damage. Elastic properties were derived using P-wave and S-wave ultrasonic transmission velocities measured in across-column directions through the damaged ice, either parallel (x(1)) or perpendicular (x(2)) to the initial loading direction. In general, as damage increased with greater strain, the ice became more compliant and (particularly freshwater ice) more anisotropic. Furthermore, with increasing strain rate, the magnitude of these effects and crack density tended to increase, in contrast to the recrystallized area fraction, which tended to decrease. We observed compliance to correspond closely with porosity and with dimensionless crack density, for strains up to 0.10. At greater levels of strain these correspondences became less clear due, in part, to the different character of the damage.