A PRELIMINARY COMPARISON OF THE PROPERTIES OF PURE ICE AND SEA ICE SINGLE-CRYSTALS

An experimental program is carried out to compare the mechanical properties of single crystals of sea ice and pure ice in order to assess the potential importance of individual crystal properties in determining the properties of polycrystalline sea ice and pure ice. The sea ice and pure ice single crystals were grown by similar techniques. Test specimens formed from these crystals had dimensions of 5 x 5 x 20 cm. Unconfined compression tests were run at constant strain rate for different c-axis and a-axis orientations to evaluate the effect of crystallographic orientation on material response. Test results showed that the ultimate stress attained by the pure ice single crystals was almost an order of magnitude higher than that for the sea ice crystals. The pure ice crystals had a steady-state flow stress almost three times as large as the sea ice crystals. The sea ice crystals showed an unexpected deformation mechanism associated with flow of brine pocket material to the crystal boundary. In general the test results indicate that much of the difference in the material properties of polycrystalline pure ice and polycrystalline sea ice may be due to the individual crystal properties rather than just due to intergranular effects.