| Résumé | High-speed imaging (30,000 images/s) has been used to observe the behavior of monocrystalline freshwater ice during crushing at -10°C. The ice contact zone consisted of an intact high-pressure central area surrounded by pulverized spall debris and partially refrozen melt. A sawtooth pattern was evident in the load record, similar to that observed in other ice crushing and indentation studies. The spalling behavior that is responsible for any particular load drop in the load record was found to be caused by the presence of small stable fractures in the high-pressure intact ice zone that were created during the preceding spall event and associated load drop. The small fractures are roughly centered in the intact ice region and this explains why the magnitude of the load drops is typically half the prior load value. The removal of ice from the intact ice zone by the viscous radial flow of a thin layer of melt has been described before (Gagnon, R.E. 1994. Melt Layer Thickness Measurements During Crushing Experiments on Freshwater Ice. Journal of Glaciology, 1994, Vol. 40, No. 134, 119-124). This process explains why the small fractures are roughly centered in the high-pressure contact zone. There the flow is stagnant and less ice has melted, relative to the non-central areas, and this leads to high non-uniform stresses in the ice that cause the fractures. |
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