Deformation and failure of ice under constant stress or constant strain-rate

Abstract

Fine-grained isotropic ice was tested in uniaxial compression at −5°C. Tests were made under: (1) constant strain rate, and (2) constant stress, with total axial strains up to about 7%. Constant rate tests for the range 10 −7 to 10 −3 s −1 gave stress/strain curves which exhibited two distinct yield points for rates up to about 10 −4 s −1. The “initial yield point”, at which internal cracks begin to form at a high rate, occurred at strains in the range 0.03–0.6%, the strain for initial yielding increasing with strain rate. A secondary yield point occurred at axial strains close to 1%. However, above 10 −4 s −1 the initial yield point became dominant and the secondary yield point disappeared. At the lowest rates (10 −7–10 −6 s −1), the secondary yield point was distinct, but the initial yield occurred at a stress level equal to, or greater than, that for secondary yield. Constant stress tests for the range 0.8–3.8 MPa gave creep curves which had a minimum strain rate at strains close to 1%. For strains less than 0.2% the resolution and data sampling were inadequate for accurate determination of strain rate as a function of time or strain, but there were fairly clear indications of another strain rate minimum in the range of 0.01%–0.1% axial strain. Direct comparison of the results for constant stress and constant strain rate suggests that the two tests give much the same information when interpreted suitably. Detailed comparisons and interpretations of the data will be given in a subsequent paper.