A MODEL FOR THE ANELASTIC STRAINING OF SALINE ICE SUBJECTED TO CYCLIC LOADING

This work formulates a model of the anelastic response of saline ice based on dislocation and grain-boundary relaxations. The dislocation-based mechanism generally dominates the behaviour, having a relaxation strength of approximately an order of magnitude greater than the grain-boundary relaxation. The latter process explains the anelasticity observed at higher frequencies and lower temperatures. An expression for the oscillatory motion of basal plane dislocations is developed that derives its temperature dependence from the dislocation drag term, which is found to be approximately the same as in freshwater ice. The results of a frequency shift analysis indicate that the dislocation relaxation may be described by a single activation energy and a distribution in relaxation time. The model applies to the region of behaviour that is approximately linear in stress. Predictions of transient and steady-state cyclic loading behaviour are examined in detail and compared with experimental observations. Aspects of the model that are still under development, related primarily to temperature effects on the microstructure and the incorporation of explicit microstructural parameters, are also discussed.