THE BRITTLE COMPRESSIVE FRACTURE OF ICE

The brittle compressive fracture under uniaxial loading of fresh-water, granular ice Ih has been studied. Measurements are reported of the fracture stress at temperatures from -10 to -50°C at strain rates of 10-3 and 10-1 s-1 for grain sizes from approximately 1 to 10 mm. Also a summary is reported of measurements by Jones et al. (unpublished) of the kinetic coefficient of friction for ice on ice at temperatures from -10 to -40°C at sliding velocities from 5 × 10-7 m s-1 to 5 × 10-2 ms-1. Observations via high speed photography of internal cracking during loading are included. The strength, albeit scattered, increases with decreasing grain size, with decreasing temperature and at -10°C with decreasing strain rate. Similarly, the coefficient of friction increases with decreasing temperature and at -10°C with decreasing sliding velocity. Wing cracks were observed on some inclined cracks nucleated during loading. The results are explained in terms of the frictional crack sliding-wing crack model [as developed by Ashby and Hallam, Acta metall. 34, 497 (1986)] of compressive fracture. Finally, a simple model is presented for the transition from ductile to brittle behavior. It is based upon the competition between the building up and the relaxation of internal stresses within the vicinity of the internal cracks, and it leads to a transition strain rate which can be expressed in terms of the fracture toughness, the creep rate, the kinetic coefficient of friction and the microstructural scale of the material. © 1990.