Crack nucleation in saline ice with interacting inhomogeneities

Abstract

The analysis of crack nucleation in saline and sea ice is complicated by the presence of local inhomogeneities such as grains and brine pockets. These inhomogeneities play an important role in the initiation of cracks from defects (precursors) located in the material. An approximate model of crack nucleation in a random microstructure which takes into account the inhomogeneities of grains and brine pockets is presented in this paper. The theoretical modeling combines an approximate method for computing microstructural stresses due to the grain elastic anisotropy and a technique for analyzing brine pocket interactions. Using these theoretical stress fields, crack nucleation is investigated with the mixed mode maximum principal stress criterion. Numerical simulations for uniaxial tensile loading show that: (i) the nucleation stresses decrease from ∼0.8 to 0.2 MPa as the porosity increases from ∼20 to 60 ppt, which are in agreement with test data for Alaskan Beaufort sea ice, (ii) precursors at triple points are subjected to a greater degree of fracture mode mixity than those on brine pockets, (iii) the circumferential stresses around brine pockets are larger than those around triple points, except for distances extremely close to the triple points where stress singularities may exist, (iv) brine pockets located at triple points may be subjected to smaller stress concentrations than those located within grains due to the complex interactions between inhomogeneities, and (v) crack nucleation is more likely to occur from brine pocket precursors but nucleation from sufficiently long triple point precursors is also possible when the brine pocket pressure is small.