The effects of Ca++ on the strength of polycrystalline ice

摘要

Recent studies have suggested a physical link between Ca++ ions and an increase in the ductility or 'softening' of polycrystalline ice. In order to investigate the potential effects of Ca++ on deformation, we created sets of both undoped and CaSO4-doped specimens of polycrystalline ice for testing in uniaxial tension or compression. Deformation tests in tension were carried out under a constant load at an initial stress of 0.75 MPa and a temperature of -6 degrees C. Compression tests were carried out at -10 and -20 degrees C at constant strain rates of 1 x 10(-4) s(-1), 1 x 10(-5) s(-1) and 1 x 10(-6) s(-1) and taken to 5% strain. Our results show that CaSO4 increases the strength of polycrystalline ice at higher strain rates and lower temperatures, an effect that decreases with decreasing strain rate and higher temperatures. A microstructural analysis of the post-test compression specimens reveals mean grain diameters much larger in the CaSO4-doped specimens tested at the lowest applied strain rate of 1 x 10(-6) s(-1). Precipitates were found to have formed along grain boundaries in some doped specimens and evidence of intergranular fracture was observed in all specimens tested at 1 x 10(-4) and 1 x 10(-5) s(-1). In tension-tested specimens, there was no difference in the mean grain diameter between doped and undoped specimens at 25% strain.