GENERATION OF MELT DURING CRUSHING EXPERIMENTS ON FRESH-WATER ICE

A stainless-steel platen, with arrays of pressure sensors and thermocouples on the front face, has been used to crush mono-crystalline, bubble-free freshwater ice samples at - 10-degrees-C and - 5-degrees-C at various constant speeds. One of the thermocouples was located at the center of the platen's central pressure transducer. Video records of the ice/steel contact zone during crushing were obtained by mounting samples on a thick plexiglas plate which permitted viewing through the specimens to the ice/steel interface. Total load and pressure records exhibited a sawtooth pattern. The relative movement of the ice towards the platen was not uniform but was much slower on the ascending side of each sawtooth, where elastic energy built up in the ice and apparatus, than on the steep descending portion, where the energy was released and the main damage of the ice occurred. This mode of periodic failure was caused by the compliance of the ice and the testing apparatus. Peak pressures were in the pressure melting range for the temperatures investigated. Contact between the platen and the ice consisted of low pressure zones of highly damaged crushed and/or refrozen ice, opaque in appearance, and regions of relatively undamaged ice, transparent in appearance, where approximately 88% of the load was borne and the pressure was greater-than-or-equal-to 70 MPa. Specific energy calculations for the ejecta extruded from high pressure zones, based on video and load records, and temperature measurements indicated that the ejecta was partially liquid and that pressure melting and heat generation by viscous flow of liquid plays an important role in ice crushing. The process was responsible for at least approximately 64% of the energy dissipated in these tests.