The friction and creep of polycrystalline ice

Abstract

The work described in this paper falls into two parts. The first is concerned with a study of the deformation of polycrystalline ice (crystal size ca. 1 mm) in uniaxial compression and when subjected to indentation. The uniaxial compression experiments covered strain ratesfrom 10 -9 to 10 -2 s -1 and temperatures from 0 to —48 °C. It is shown that over the whole range of experimental conditions the secondary creep behaviour can be described by a single relation of the type where o is the applied stress, Q an activation energy an d A, a and n are suitable constants. This reduces to the more familiar power law over more restricted portions of the experimental curve. Over the whole range n has a value close to 3 but Q has two distinct values: 120 J mol -1 above — 8 °C: 78 J mol -1 below —8 °C. The in dentation hardness experiments cover loading-times from 10 -4 to 104 s and a temperature range of 0 to — 25 °C. The hardness behaviour may be linked with the creep properties using the analysis of Atkins, Silverio & Tabor (1966) which assumes that the rate-determining process is the diffusion of the hemispherical elastic-plastic zone surrounding the indenter into the undeformed material ahead. There is very good agreement between the hardness data and the creep parameters determined in the uniaxial compression experiments. In addition the hardness experiments enable experiments to be carried out at much higher compressive stresses.