The influence of water, snow and granular ice on ice failure processes, ice load magnitude and process pressure

Abstract

This paper describes the outcomes of a series of laboratory ice crushing experiments that was performed (Sopper, 2016) to investigate the effects of external boundary condition and indenter contact geometry on ice load magnitude under crushing conditions. Four boundary conditions were considered: dry cases, submerged cases, and cases with the presence of snow and granular ice material on the indenter surface. Indenter geometries were a flat plate, wedge shaped indenter, (reverse) conical indenter, and a hemispherical indenter. These were impacted with artificially produced ice specimens of conical shape with 20° and 30° cone angles. All indenter – ice combinations were tested in dry and submerged environments at 1mm/s and 100mm/s indentation rates. Additional tests with the flat indentation plate were conducted at 10mm/s impact velocity and a subset of scenarios with snow and granular ice material was evaluated.The tests were performed using a material testing system (MTS) machine located inside a cold room at an ambient temperature of –7°C. Data acquisition comprised time, vertical force, and displacement. In several tests with the flat plate and wedge shaped indenter, supplementary information on local pressure patterns and contact area were obtained using tactile pressure sensors. All tests were recorded with a high speed video camera and still photos were taken before and after each test. Thin sections were taken of some specimens as well.Ice loads were found to strongly depend on contact condition, interrelated with pre-existing confinement and indentation rate. Submergence yielded higher forces, especially at the high indentation rate. This was very evident for the flat indentation plate and spherical indenter, and with restrictions for the wedge shaped indenter. No indication was found for the conical indenter. The presence of snow and granular ice significantly increased the forces at the low indentation rate (with the flat indentation plate) that were higher compared to submerged cases and far above the dry contact condition.Contact area measurements revealed a correlation of higher forces with a concurrent increase in actual contact area that depended on the respective boundary condition. In submergence, ice debris constitution, ice extrusion, as well as crack development and propagation were impeded. Snow and granular ice provided additional material sources for establishing larger contact areas. The dry contact condition generally had the smallest real contact area, as well as the lowest forces. The comparison of nominal and measured contact areas revealed distinct deviations which were dependent on the boundary conditions. The incorporation of those differences in contact process pressures-area relationships indicated that the overall process pressure was not substantially affected by changes in true contact area.