Disintegration of ice under fast compressive loading

Abstract

During the interaction of ice with ships or other offshore structures, a compressive zone develops in the ice. This is the focus of the present work. An interpretation of field measurements shows that the compressive ice load is far from uniform; indeed, most of the load is transmitted through small areas of intense pressure characterized by a highly damaged layer. The processes leading to the formation of these zones include fractures, and in particular spalls near the edges of the zones, as well as a separate process of damage and microstructural change within the layer itself. In order to capture the essential points for deducing design requirements, we have formulated a probabilistic model of high-pressure zones. The mechanics of failure of ice in these zones is explored. Triaxial tests have been conducted. Mechanisms discussed include microcracking (shear banding), recrystallization and grain boundary melting. As pressures increase, the microcracking and recrystallization are suppressed and the strain rates decrease. At even higher pressures, the results show pressure softening with enhanced strain rates. Two state variables are used to model the ice deformation, corresponding to the hardening at lower pressures, and to the softening at higher pressures. Finite element analyses of the ice response incorporating these variables, corresponding to a medium scale indentation test have yielded promising results, showing the decline in load and the layer formation.