The Mechanical Properties of Freshwater Ice

In Nature, deformation of ice occurs at over 80% of its melting point. The strength of ice decreases rapidly with increasing temperature and shows a Hall-Petch relationship with the grain size. Based on creep tests Glen (1955) first developed a flow law for the secondary creep of polycrystalline ice in which the strain rate, ε ̇, is related to the stress, s, through ε ̇=Aσ^n, where the stress exponent, n » 3. However, some more recent studies of polycrystalline ice have indicated values of n from 1-4 depending on the temperature and grain size. In contrast, deformation of single crystal ice generally shows n » 2. Deformation of ice is largely controlled by dislocation glide on the basal plane, which has been suggested to be related to the rate of hydrogen-bond reorientation. The CRSS for non-basal slip is almost two orders of magnitude higher than that for basal slip. Thus, the flow of polycrystalline ice is strongly affected by grain orientation, which changes during deformation both due to slip-plane rotation and to recrystallization, which can occur at strains of a few percent. It is well established that the Earth’s large continental ice sheets contain a variety of naturally-occurring impurities, both soluble and insoluble, both of which can have substantial effects on the flow of ice. This presentation will review both the phenomenology and mechanisms of ice deformation with an emphasis on the effects of both soluble impurities and particles.

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