MICROCRACKING DUE TO GRAIN-BOUNDARY SLIDING IN POLYCRYSTALLINE ICE UNDER UNIAXIAL COMPRESSION

This paper examines grain boundary sliding as a mechanism for nucleati on 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 resulti ng boundary value problem solved using the finite element method. Simu lations show that by allowing grain boundary sliding a defect originat ing at the triple point grows stably, reaches a critical length and th en propagates unstably to the neighboring triple point. The influence of the elastic mismatch between neighboring grains on microcracking st ress is not strong. The stress causing microcrack growth is found to b e inversely proportional to the square root of the grain size. If no g rain sliding takes place, and only the elastic anisotropy mechanism op erates, the stresses required for microcrack nucleation and growth are unrealisticly high; the resulting microcracks are also too short.