Time lapse photography Glaciers Dislocations Bernal-Fowler rule Generation of defect structures Crystal structures Crystal structures Ice Basal glide Strain rate for glide on basal systems Critical resolved shear stress Non-basal glide Non-basal glide Diffusional flow Plastic Deformation Primary creep Secondary creep Tertiary creep Deformation maps Grain growth and grain size reduction Anisotropic flow Index
Non-basal Glide
When a load is applied to an ice crystal such that there is no resolved shear stress on the basal plane, the rate of deformation is so slow that it is extremely difficult to detect. The propagation of dislocations through non-basal systems is not well understood, however deformation experiment on monocrystals by Nakaya (1958), Wakahama (1966), and Higashi (1966) indicate that non-basal systems require at least two orders of magnitude more stress to initiate glide that basal systems (see fig. 2.11.1). Hutchison (1977) suggests that glide may occur on both prismatic {0110} 2110 and pyramidal {1122} <1123> slip systems (see fig. 1.1.2). Weertman (1973) estimates that non-basal glide is 100 - 1000 time more difficult that basal systems, while Castelnau et al. (1996) suggests that the prismatic slip system requires 20 times more resolved shear stress to initiate glide than the basal systems and the pyramidal systems require 200 time more resolved shear stress than basal systems (see fig. 1.1.2).
 
Figure 2. 11. 1
Figure 2.11.1. Data for glide on basal and non-basal systems, and in isotropic polycrystalline ice
compiled by Duval et al. (1983). Non-basal glide data shows the low boundary for stress giving rise
to deformation and may not represent the true stress required for the observed strain rates.
 
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Created: August 23, 1999
Last modified: March 15, 2004
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