Effect of microcracking on the deformation of ice

Abstract

Tests in the field and full-scale experience with arctic structures show that the crushing of ice is accompanied by large fluctuations in load. Field experiments show that, in addition to variations of load in time, significant spatial variations across the contact surface also occur. The deformation is observed to take place in a thin layer of damaged ice, which appears near the structure or indenter surface. It is important to model the deformation and strength of ice in this zone. Various aspects of modelling are discussed in the paper, in particular, measures of damage and the relation to the deformation of ice. The relevance of various components of deformation (elastic, viscous, delayed elastic) is outlined, and two mathematical formulations for the deformation are discussed. The behaviour was investigated by a series of tests at constant strain rate as well as tests in which the strain response to stress of damaged and undamaged ice was measured. The creep rate in damaged ice is shown to be significantly enhanced, even for short-term loading. Comparisons of theory and experiment are given for constant strain-rate tests. The models have been calibrated to the experimental data described in the paper. It is a matter for future research to generalize the models to all damage levels and stress states. Key words : creep, damage, deformation, ice, microcracking, visco-elasticity.