In ice mechanics, it is recognised that, at low strain rates, polycrystalline ice undergoes time and temperature dependent deformation with ductile mode of failure. At high strain rates, however, ice behaves as a linear elastic material with a brittle mode of failure. This paper presents the formulation for a general constitutive model that has the capability to predict both ductile and brittle failure modes of ice. The ductile model is based on the principles of the rate theory for fracture kinetics, while the brittle model was formulated using an elliptical failure surface. Historically, Krausz and Krausz (1989) developed a rate theory for damage mechanics in metals. Derradji-Aouat (1992) modified and migrated the theory to model structural damage in polycrystalline ice. Subsequent analysis (Derradji-Aouat et al., 2000) showed that the modified theory predicts very well the progressive damage behaviour of ice at low strain rates, but it cannot predict its brittle fracture at high strain rates (>10~3/s). They concluded that their progressive damage model needs to be complemented by a criterion for the brittle failure of ice. A preliminary formulation for a brittle failure stress criterion for ice was proposed by Derradji-Aouat (2000a). In this paper, that failure criterion is modified so that it can be combined with the progressive damage model. This results in a general model that is capable to predict the behaviour and failure of ice at any given strain rate (low or high strain rates). It is aimed that this general model will be used as the ice material routine in the numerical simulations of collisions between ice floes and icebergs with oil tankers and offshore structures in the Grand Banks off the coast of Newfoundland and Labrador, Canada (Derradji-Aouat, 2000b).
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