Abstract
Abstract. It is vital to understand the mechanical properties of flowing ice to model the dynamics of ice sheets and ice shelves and to predict their behaviour in the future. We can increase our understanding of ice physical properties by performing deformation experiments on ice in laboratories and examining its mechanical and microstructural responses. However, natural conditions in ice sheets and ice shelves extend to low temperatures (≪-10 ∘C), and high octahedral strains (> 0.08), and emulating these conditions in laboratory experiments can take an impractically long time. It is possible to accelerate an experiment by running it at a higher temperature in the early stages and then lowering the temperature to meet the target conditions once the tertiary creep stage is reached. This can reduce total experiment run-time by > 1000 h; however it is not known whether this could affect the final strain rate or microstructure of the ice and potentially introduce a bias into the data. We deformed polycrystalline ice samples in uniaxial compression at −2 ∘C before lowering the temperature to either −7 or −10 ∘C, and we compared the results to constant-temperature experiments. Tertiary strain rates adjusted to the change in temperature very quickly (within 3 % of the total experiment run-time), with no significant deviation from strain rates measured in constant-temperature experiments. In experiments with a smaller temperature step (−2 to −7 ∘C) there is no observable difference in the final microstructure between changing-temperature and constant-temperature experiments which could introduce a bias into experimental results. For experiments with a larger temperature step (−2 to −10 ∘C), there are quantifiable differences in the microstructure. These differences are related to different recrystallisation mechanisms active at −10 ∘C, which are not as active when the first stages of the experiment are performed at −2 ∘C. For studies in which the main aim is obtaining tertiary strain rate data, we propose that a mid-experiment temperature change is a viable method for reducing the time taken to run low-stress and low-temperature experiments in the laboratory.
Highlights
1.1 BackgroundIce is a mechanically anisotropic material, meaning that its mechanical properties change with direction
The purpose of this study is to compare the microstructural and mechanical data from laboratory ice compression experiments conducted at a single temperature to experiments conducted at multiple temperatures, to establish the extent to which microstructural characteristics of laboratory ice deformed to tertiary creep at one temperature persist once the temperature changes
The seed grains were poured into a mould, which was flooded with water at 0 ◦C and carefully agitated to remove bubbles
Summary
1.1 BackgroundIce is a mechanically anisotropic material, meaning that its mechanical properties change with direction. It undergoes microstructural changes in response to changing stress and temperature conditions (here we define “microstructure” as the small-scale structure of the ice, including what is often referred to in materials science as “fabric” and “texture”). This microscale anisotropy leads to largescale anisotropy of larger ice masses like ice shelves and streams and affects their response to external changes such as those related to climate change (Castelnau et al, 1998; Harland et al, 2013). Measuring the mechanical and microstructural properties of deforming ice under different conditions is an important process, but it can take an unreasonable length of time (months to years)
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