Author(s): R. C. Picu; V. Gupta

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Abstract: Stress singularities at grain triple junctions are obtained in a two dimensional polycrystal for random triple-junction geometries and various orientations of the cubic and orthotropic grains. By using a finite element model, the energy release rate for nucleating a crack is also obtained for the triple-junction configuration with the largest singularity. In these calculations, such a junction is embedded in an overall elastic matrix and the cracking event is sought under biaxial compression with different confinement ratios. Although the current calculations improve upon our prior efforts where the grains were assumed to be isotropiC with different moduli, the overall conclusions remain unaltered. The energy release rate values are far below to encourage nucleation from the triple junctions in freshwater ice. Similarly, when the effects of brine pocket shape, size and distribution are alI smeared into a homogeneous orthotropic grain, the calculated energy rate values fall much short of those required for nucleation. Thus the brine pockets remain as the crack nucleation sites in saline ice, whereas other mechanisms like grain boundary sliding may govern the nucleation process in freshwater columnar ice.

DOI:

Year: 1994