Three-dimensional stress concentration at grain triple junctions in columnar ice

The magnitude of the elastic anisotropy-induced stress concentration at points where the grain triple-junction lines in freshwater columnar ice intersect the free surface is analysed. The concentration effect is shown to be much weaker than that at the crack tip but stronger than obtained at similar grain triple junctions under plain-strain conditions. If preferential thermal etching of the ice surface occurs at the triple junction, the grooving and the elastic anisotropy effects add and significantly stronger concentrations result. The conditions under which cracks are expected to nucleate from these stress concentration sites are discussed.