Analysis of Medium-Scale Laboratory Tests on Ice Crushing Dynamics

Abstract

The study of ice loads and associated mechanics is highly important in supporting oil and gas exploration and development in ice-prone offshore regions. While knowledge gaps regarding full details of the dynamic ice structure interaction process remain, substantial research is being carried out over a range of scales to improve understanding of excitation mechanisms for structures subjected to compressive ice loading. The present paper is focused on the first of a new series of medium-scale laboratory tests that have been carried out as a part of a larger program of research aimed at improving understanding of compressive ice failure phenomena and links between the formation of high-pressure zones and the occurrence of ice-induced structural vibrations under controlled conditions. The tests presented in this paper focus on the indentation of ice using a single spherical indenter mounted on a compliant beam system. Nine tests were performed to investigate the effect of ice temperature and indenter size on ice failure processes associated with high-pressure zone formation and evolution during dynamic ice crushing tests. Ice failure events were observed from regular and high-speed video synchronized with LVDTs and load cell data. Observations of ice load dynamics and structural response are discussed, along with corresponding observations of failure processes in the ice. In general it was observed that ice at warm temperatures was more prone to ductile type failure with lower, less dynamic pressures. By contrast, results from tests conducted at colder temperatures were characterized by a combination of spalling and crushing failure, which corresponded more with large-amplitude, sawtooth load cycles, which often resulted in load drop to zero as the rebounding structure cleared the failed ice from around the indenter. In terms of scale effects, it was observed for the same indentation rate and temperature, smaller indenters produced higher amplitude, higher frequency sawtooth loading than was observed for larger diameter indenters.