A combined creep and yield model has been developed for ice in a multiaxial stress state. The equations of the model describe the entire creep process, including primary, secondary, and tertiary creep, at both constant stresses and constant strain rates in terms of normalized (dimensionless) time t = t/tm. Secondary creep is considered an inflection point defining the time to failure (tm), The minimum strain rate at failure is described by a modified Norton-Glen power equation, which, as well as the time to failure, includes a parabolic yield criterion. The yield criterion is selected either in the form of an extended von MisesDrucker- Prager or an extended Mohr-Coulomb rupture model. The criteria take into account that at a certain magnitude of mean normal stresses (σmax) the shear strength of ice reaches a maximum value due to local melting of ice. The model has been verified using test data on yield of polycrystalline ice at −11.8°C and on creep of saline ice at −5°C, both under triaxial compression (σ2 = σ3).
The successful solution of ice engineering problems depends greatly upon the accuracy of the constitutive laws and failure criteria of ice used in analyses of engineering structures. Two approaches can be distinguished in describing the deformation and failure processes of ice in uniaxial as well as multiaxial stress states. In the first (traditional) approach, it is assumed that the total creep shear strain γC can be broken down into four components: (equation 1 shown in paper) where γe, γp, γv and γt are elastic, primary, secondary, and tertiary pure shear strain, respectively. The failure process, particularly time to failure, is either not considered (in most cases) or is assumed to take place in the later, secondary or tertiary stages of creep.
