Experimental investigation of compressive failure of truncated conical ice specimens

Abstract

In total, twenty-eight (28) small-scale ice indentation tests have been carried out to study the compressive failure of polycrystalline ice during indentation and to explore the link between various parameters that influence the ice failure processes, using ice specimens having a truncated conical geometry. Taper angle, temperature, indentation rate, indenter shape and grain size are considered as controlled variables in this research program. For the experiments, three geometric configurations (with taper angles of 13°, 21°, 30°) have been used, conducted at temperatures of -10°C and -5°C. Indentation rates of 0.1 mm/s, 1 mm/s and 10 mm/s have been considered using two indenter shapes (a flat plate and a spherical indenter). Two grain size ranges were considered for these tests. The total force and pressure were found to show dependencies on the indentation rate. The force becomes higher and failure process changes from brittle to ductile as indentation rate decreases. For example, in case of the 21º taper angle ice sample, maximum ice loads were 20 kN and 145 kN and peak pressures were 8 MPa and 18 MPa for indentation speeds of 10 mm/s and 0.1 mm/s respectively. The total force also depends on the taper angle of ice sample. The loads increase as the ice samples become flatter. So, the 13° ice sample was stronger than the 30° ice sample. Different shaped indenters also observed to have distinct experimental outputs. Tests that were done using the spherical indenter show lower forces than the tests that were done using the flat indenter. Effects of temperature reveal that the warm tests show a greater tendency to ductile failure than cold tests having same parameters. The ice samples with smaller ice seeds need more force to fail compared to ice samples with bigger ice seeds. To observe the microstructural modification, horizontal and vertical thin-sections of the damaged ice adjacent to the indenter have been examined. Ice particles were collected from the testing area following each experiment to observe the influence of different factors on the particle size distributions. The effect of each variable on observed failure processes and associated loads are presented in the thesis.