Microcracking due to grain boundary sliding in polycrystalline ice under uniaxial compression

This paper examines grain boundary sliding as a mechanism for nucleation and growth of microcracks in polycrystalline S2 ice, under uniaxial compression. The loading rate is fast enough so that the polycrystal response is almost linear. A unit cell model is set up and the resulting boundary value problem solved using the finite element method. Simulations show that by allowing grain boundary sliding a defect originating at the triple point grows stably, reaches a critical length and then propagates unstably to the neighboring triple point. The influence of the elastic mismatch between neighboring grains on microcracking stress is not strong. The stress causing microcrack growth is found to be inversely proportional to the square root of the grain size. If no grain sliding takes place, and only the elastic anisotropy mechanism operates, the stresses required for microcrack nucleation and growth are unrealisticly high; the resulting microcracks are also too short.