A MODEL FOR THE ANELASTIC STRAINING OF SALINE ICE SUBJECTED TO CYCLICLOADING

This work formulates a model of the anelastic response of saline ice b ased on dislocation and grain-boundary relaxations. The dislocation-ba sed mechanism generally dominates the behaviour, having a relaxation s trength of approximately an order of magnitude greater than the grain- boundary relaxation. The latter process explains the anelasticity obse rved at higher frequencies and lower temperatures. An expression for t he oscillatory motion of basal plane dislocations is developed that de rives its temperature dependence from the dislocation drag term, which is found to be approximately the same as in freshwater ice. The resul ts of a frequency shift analysis indicate that the dislocation relaxat ion 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 wi th experimental observations. Aspects of the model that are still unde r development, related primarily to temperature effects on the microst ructure and the incorporation of explicit microstructural parameters, are also discussed.