CRACK VELOCITIES IN FRESH-WATER AND SALINE ICE

This paper presents experimental results on both mode 1 and 2 crack ve locities measured in a wide variety of ice types, columnar sea ice, co lumnar lake ice, laboratory-grown columnar saline ice, and freshwater columnar and granular ice, in the temperature range from -5 degrees to -35 degrees C. Measurements of ice electrical conductance, electrical capacitance, and electromagnetic emissions from cracks as a function of time were used to determine crack velocities in samples with dimens ions ranging from 0.05 to 30 m. In laboratory-grown freshwater ice and in lake ice, average crack velocities varied from a few hundred to 13 20 m/s. In contrast, in natural sea ice and laboratory-grown saline ic e, crack velocity was very low at about 10 m/s. This remarkable differ ence in the velocity of cracks growing in freshwater and saline ice is probably due to the dynamic resistance of unfrozen water in brine poc kets and/or the large size of a crack tip process zone in saline ice. It was also found that cracks propagate discontinuously in saline ice owing to the strong interaction with microstructural elements such as drainage channels.