Compressive failure mechanics of ice during particle embedment

Fitzpatrick, Thomas (2024) Compressive failure mechanics of ice during particle embedment. Masters thesis, Memorial University of Newfoundland.

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Abstract

In total, sixty-six (66) single particle tests were conducted with up to 10 repetitions per setpoint, and fifty-five (55) multi-particle tests were conducted including repetitions with twenty-five (25) being completed on pristine ice specimen. These small-scale ice-particle indentation tests have been completed in order to study the compressive failure of polycrystalline ice during rock indentation. These tests were conducted using a population of rock particles to explore the link between various parameters that influence the ice failure processes and the effect that the presence of these rocks may have on them. In this research program, parameters such as average rock diameter, temperature, indentation rate, indentation depth, and relative spacing of indentation zones from previously formed damage zones are considered as controlled variables. For all experiments, rocks were taken from a population with diameters which were determined to be between 3/8” and 3/4”, based on statistical analysis of the population. Three setpoint indentation rates were imposed, a slow rate of 0.01 mm/s, a moderate rate of 0.5 mm/s, and a fast rate of 10 mm/s. While for single particle indentation tests multiple rates were investigated, only a single representative rate of 0.5 mm/s was implemented for multi-particle tests. Tests were conducted at a nominal setpoint temperature between -10°C and -13°C. Single particle tests were completed at indentation positions 2D (26 mm). 5D (65 mm), and 7D (96 mm) away from previously formed damage zones, based on an average diameter D of 13mm. Two grain size ranges were considered for these tests. The total force and pressure were found to show dependencies on the indentation rate. Multi-particle tests were completed with constant weighed population of 170-grams of rocks taken from the same population of diameters between 3/8” and 3/4”. Analysis on all results obtained in the form of force trace data from the MTS, pressure data determined based on the forces observed, and analysis of images taken after indentation has been completed. Representative cases are outlined and described in this work for each combination of constants. Further analysis was completed on the outcomes of both multi-particle and single particle indentation tests, as well as comparisons between the two. Strong rate dependence was observed in the force and pressure data for single particle indentation tests, with observed forces and pressures trending upwards with increased rate until 0.5 mm/s and subsequently decreasing as rates approached 10 mm/s. These forces and associated trends from the MTS data were noted to be consistent with those observed during spherical steel indenter tests reported in the literature, and a comparison between the two is presented in this work. It was also determined that the effect of spacing from previously formed damage zones on single particle indentation was not significant; therefore, indentation events were assumed to be approximately independent. This was examined further based on a comparison with multi-particle indentation tests, since the trends observed in the data traces from these tests were consistent with those observed during single-particle testing. This led to the development of an empirical model which simulated multiparticle indentation based on an aggregation of previously completed single particle indentation tests. Using the assumption of independent indentation events, the simulated multi-particle events were compared with test data from laboratory experiments on multi-particle indentation. These comparisons yielded strong similarities between simulated and experimental results, further supporting the assumption of independence of indentation events for multi-particle indentation. The outcomes of this research will support a deeper understanding of the mechanics of a collision between offshore structure and ice feature with embedded rocks. Full details of these investigations are presented in this thesis.

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