Failure envelope of first‐year Arctic sea ice: The role of friction in compressive fracture

Abstract

New experiments have been performed on the brittle compressive failure of columnar‐grained, first‐year sea ice with the S2 growth texture, harvested from the floating cover on the Arctic Ocean. The ice was proportionally loaded biaxially across the columns at –10°C at 1.5 × 10−2 s−1; i.e., within the regime of brittle behavior. The results, when combined with earlier measurements of tensile strength by Richter‐Menge and Jones (1993), allow the complete brittle failure envelope to be constructed. The envelope is symmetric about the loading path R = σ2/σ1 = 1, owing to the isotropic character of the material within the horizontal plane of the ice sheet, but is asymmetric with respect to the compressive‐compressive and tensile‐tensile quadrants, owing to the relative weakness of the material under tension. The compressive strength reaches a maximum along the loading path R ∼ 0.5. Terminal failure occurs through either splitting (unconfined loading), Coulombic shear faulting under lower confinement (R < 0.2) or spalling under higher confinement (0.2 < R ≤ 1). An integral component of compressive failure under low confinement is the internal friction coefficient: its value under the conditions of the experiments (μi = 0.92 ± 0.09) is deduced from the failure envelope. The internal friction coefficient is shown through postterminal failure measurements to be closely similar to the coefficient of friction at the onset of sliding along the Coulombic faults. Granite exhibits similar behavior. Modeling reveals that the terminal failure stress under low confinement can be reasonably well described in terms of the comb‐crack mechanism (Schulson et al., 1999; Renshaw and Schulson, 2001) of brittle compressive failure. Comparison with observations and measurements in the field indicate that the failure processes that operate on the smaller scale are similar to at least some of those that operate on the larger scale, implying that the physics of failure may be scale‐independent.