Real-time observations of the microstructural evolution in compressed ice

Galway, Kurtis (2024) Real-time observations of the microstructural evolution in compressed ice. Masters thesis, Memorial University of Newfoundland.

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Abstract

A total of fourteen (14) small-scale compression tests have been conducted using a specially designed apparatus in order to observe the processes which alter the microstructure of the ice due to an applied stress. All tests were conducted using a 5 MPa load applied to a 0.8mm thick, 60mm diameter ice sample. Tests were conducted at temperatures of -10°C to 0°C, -10°C to -2°C, -15°C to -20°C, and 0°C. These tests were then compared to a base case in which the ice sample temperature was allowed to change from -10°C to 0°C without any applied load. Various processes which impact the structure of the ice were observed in real-time using a borescope camera, and the videos were analyzed following the test. Cracking occurred in all tests and was dependent on the ice temperature. Ice at -10°C cracked in one short event indicating sudden brittle fracture, while ice closer to the melting point and ice at -15°C was time-dependent and cracked over the course of minutes. Crack healing is observed in two cases: as a result of prolonged application of stress and the resulting creep, and due to pressure melting at temperatures close to the melting point. Grain nucleation was the dominant dynamic recrystallization process at temperatures less than around -3°C and always occurred in response to the applied stress. At temperatures within -3°C of the melting point, grain boundary migration became the dominant recrystallization process. Pressure melting is observed to occur at temperatures within -0.1°C of the melting point. Generally, processes occurred at faster rates at warmer temperatures closer to the melting point. An in-depth analysis of the observed processes is presented in this thesis.

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