EFFECTS OF SURFACE CONDITION ON MECHANICAL PROPERTIES OF ICE CRYSTALS

A comparative study of the deformation behaviour of mechanically and chemically polished ice crystals is described. For single crystals, mechanical disturbance of the surface layer greatly reduces the maximum stress for basal glide in constant strain rate tests in compression. Single crystals with sub-boundaries do not show any prominent surface effect, but exhibit quite a low maximum stress. The results indicate that mechanically disturbed surface layers and sub-boundaries do not appear to act as strong barriers to dislocation movement in ice crystals, but rather as sources of dislocations. Surface condition does not appear to affect the maximum stress for polycrystals. The influence of strain rate (range 2·1 × 10-5 to 1·7 × 10-4 s-1) and temperature (range -10 to -30°C) upon the maximum stress was also investigated for both single crystals and polycrystals of ice.