Superplasticity in ice
Abstract
A series of 1 atm creep experiments was conducted to reliably determine constitutive equations for the flow of ice that include grain size creep mechanisms. Experiments were conducted over the following ranges of stress, temperature, grain size and strain rate, respectively: 0.2≤sigma≤ 20 MPa, 170≤ T≤ 268 K, 3≤ d≤ 200\ mum, and 1× 10sp{-8}≤dotvarepsilon≤ 1× 10sp{-4}\ ssp{-1}. At high stresses, greater than 3-5 MPa, the creep of fine-grained ice is dominated by dislocation creep processes. With decreasing stress, a transition occurs from dislocation creep to dislocation-accommodated grain boundary sliding (GBS). At the lowest stresses, less than ∼0.3 MPa, another transition occurs to a GBS-dominated regime in which the creep rate is limited by the movement of dislocations on the easy (basal) slip system. The flow of ice is well-described by a constitutive relationship that includes the contributions of dislocation creep, dislocation-accommodated GBS, easy slip-limited GBS, and diffusion-accommodated GBS. Extrapolation of this constitutive equation to larger grain sizes pertinent to the planetary and glaciological environment demonstrates that dislocation-accommodated GBS and dislocation creep are the dominant creep mechanisms in ice over a wide range of conditions, and that the transition to diffusion-accommodated GBS for coarse-grained ice occurs at insignificantly small stresses and slow strain rates. Hence, the flow of ice in the planetary and glaciological environment is dominated by dislocation and dislocation-accommodated GBS processes.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1998
- Bibcode:
- 1998PhDT.......177G