Fracture, Friction, and Permeability of Ice

Water ice Ih exhibits brittle behavior when rapidly loaded. Under tension, it fails via crack nucleation and propagation. Compressive failure is more complicated. Under low confinement, cracks slide and interact to form a frictional (Coulombic) fault. Under high confinement, frictional sliding is suppressed and adiabatic heating through crystallographic slip leads to the formation of a plastic fault. The coefficient of static friction increases with time under load, owing to creep of asperities in contact. The coefficient of kinetic (dynamic) friction, set by the ratio of asperity shear strength to hardness, increases with velocity at lower speeds and decreases at higher speeds as contacts melt through frictional heating. Microcracks, upon reaching a critical number density (which near the ductile-to-brittle transition is nearly constant above a certain strain rate), form a pathway for percolation. Additional work is needed on the effects of porosity and crack healing. ▪ An understanding of brittle failure is essential to better predict the integrity of the Arctic and Antarctic sea ice covers and the tectonic evolution of the icy crusts of Enceladus, Europa, and other extraterrestrial satellites. ▪ Fundamental to the brittle failure of ice is the initiation and propagation of microcracks, frictional sliding across crack faces, and localization of strain through both crack interaction and adiabatic heating.