Studies were carried out on deformation and failure of ice under monotonic loading (0 = crt). A constitutive equation, a strength criterion and a failure strain criterion were developed for ice under constant stress rate (a = const.). The constitutive equation was developed by expansion of the modified primary creep model at constant stress over the monotonic loading regime. The model has been verified using published data from uniaxial compression tests of freshwater columnar-grained ice under various constant stress rates at -10°C. It is shown that the parameters of the model are interrelated and are in agreement with those obtained from previous creep tests of ice at constant stress.
In technical literature, creep of ice is often defined as a process of accumulation of ice deformation with time while the applied stress remains constant (0 = const.). However, creep deformations and failure of ice can also take place under loading regimes different from constant stress, such as a constant stress rate (cr = const.) (monotonic loading) or step loading. The latter can be defined as monotonic loading when the time duration of each loading step (or stage) approaches zero. Previous investigations (Zaretski and Fish, 1973; Fish 1982) showed a close relationship between rheological parameters of ice determined from conventional creep tests at constant stress and tests under steadily increasing stresses (step loading regime). Note that there is a substantial difference between conventional creep tests and tests under monotonic loading. Indeed, a conventional creep curve consists of three stages: primary, secondary and tertiary, although secondary creep can be assumed to be an inflection (failure) point on a creep curve (Fish, 1984, 1987, 1992), while a deformation curve under monotonic loading consists of only one stage without visible critical points that may be associated with failure.
