Investigation of the role of freeze bonds on the development of ice rubble strength

Boroojerdi, Marjan Taghi (2020) Investigation of the role of freeze bonds on the development of ice rubble strength. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Freeze bonds are one of the controlling factors in ice ridge and rubble failure. Strength and failure properties of freeze bonds are therefore important to study, to better understand the overall strength development of ice ridges/rubble. This research aims to understand the strength development and failure of freshwater freeze bonds through a series of experiments, conducted under different conditions of contact time, deformation rate, and confinement pressure. Freeze bonds were formed between two cylindrical ice samples, confined under a normal pressure at the two ends, which were submerged in a freshwater bath for a specific period of time. Freeze-bonded samples were then sheared using the Asymmetric Four-Point Bending (AFPB) apparatus installed on the Materials Testing System (MTS) servo-hydraulic testing machine at Memorial University’s coldroom. Increasing the submersion time from 1 minute to 14 days, freeze bond strength was observed to be initially controlled by heat transfer processes, increasing with submersion time and reaching a peak after 5 minutes. Strength then decreased as ice reached equilibrium temperature with surrounding water, after which it remained constant. Sintering and creep processes were believed to be the dominating mechanism in long submersion times, resulting in an increase in strength after 1 day, until reaching the strength of solid ice after 14 days. Confinement pressure effects were investigated for four different submersion times that were chosen based on the stages of bond development observed in the submersion time tests. Strength values increased linearly as confinement increased from 10 to 100 kPa for all submersion times tested. The rate of this increase followed the trends observed in submersion time tests, with the highest amount of increase occurring after one week of submersion. Sintering-creep and crushing of asperities in contact were introduced as the responsible processes, which are known to be intensified with increase in confinement and contact time. Increasing the deformation rate during shear from 0.01 to 100 mm/s, freeze bond failure strength was observed to decrease. This decrease was associated with higher amounts of strain before failure of freeze bonds at lower deformation rates, which is a result of the higher capacity of energy dissipation and creep at lower rates. Ice rubble and ice ridge experiments studied to date follow similar trendlines of strength-confinement and strength-deformation rate observed in present study, which highlights the important role of block to block freeze bond strength development and failure on the overall strength properties of ice rubble/ridges.

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