GENERATION OF MELT DURING CRUSHING EXPERIMENTS ON FRESH-WATER ICE

A stainless-steel platen, with arrays of pressure sensors and thermoco uples on the front face, has been used to crush mono-crystalline, bubb le-free freshwater ice samples at - 10-degrees-C and - 5-degrees-C at various constant speeds. One of the thermocouples was located at the c enter of the platen's central pressure transducer. Video records of th e ice/steel contact zone during crushing were obtained by mounting sam ples on a thick plexiglas plate which permitted viewing through the sp ecimens to the ice/steel interface. Total load and pressure records ex hibited a sawtooth pattern. The relative movement of the ice towards t he 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. Pe ak pressures were in the pressure melting range for the temperatures i nvestigated. Contact between the platen and the ice consisted of low p ressure zones of highly damaged crushed and/or refrozen ice, opaque in appearance, and regions of relatively undamaged ice, transparent in a ppearance, where approximately 88% of the load was borne and the press ure was greater-than-or-equal-to 70 MPa. Specific energy calculations for the ejecta extruded from high pressure zones, based on video and l oad records, and temperature measurements indicated that the ejecta wa s partially liquid and that pressure melting and heat generation by vi scous flow of liquid plays an important role in ice crushing. The proc ess was responsible for at least approximately 64% of the energy dissi pated in these tests.