Crack nucleation in polycrystalline ice

Abstract

This paper examines in detail two likely mechanisms of microcrack formation in polycrystalline ice and pays special attention to the grain size dependencies of each mechanism. Under consideration are the Zener-Stroh dislocation pileup mechanism and an elastic mechanism based on the anisotropy of the ice lattice. Calculations for the pileup mechanism indicate that although the dislocation velocity is relatively low, a critical-sized pileup can form under plausible test conditions. Quantification of the elastic anisotropy mechanism indicates that it operates over approximately the same stress levels as the pileup mechanism and exhibits the same grain size dependency. The results of observations on the microcracking of laboratory-prepared freshwater ice having randomly oriented equiaxed grains are used to test the model predictions. The work gives detailed descriptions of the methods used to quantify each model.