The role of phase transformations as a softening mechanism in saline ice

To gain insight into the behavior of saline ice relative to non-saline ice, single crystals of saline and non-saline ice were loaded in compression. Responses from these experiments indicate that single crystals of saline ice are significantly more compliant during the initial load response. Analyses presented in this dissertation indicate that phase transformations in brine cells have the potential to play a significant role in increasing the compliance of saline ice during the initial load response.; Cooling of a sealed brine cell, leading to the precipitation of ice, provides a mechanism for the accumulation of "large" localized stresses. Based on mathematical models, this mechanism has the potential to be a significant source for the nucleation or multiplication of dislocations, and can conceivably make a significant contribution to the greater compliance (softness) of saline ice relative to non-saline ice. These results are consistent with the observation that laboratory grown saline crystals sometimes display extensive differences in mechanical behavior that appears to be due to variations in the growth and storage conditions experienced by the crystals.; The brine cell model presented in this dissertation indicates that there is a transition in deformation modes for brine cell cooling rates on the order of 0.1 {dollar}spcirc{dollar}C hr{dollar}sp{lcub}-l{rcub}.{dollar} At lower rates, local deformation is dislocation dominated; at higher rates, it is fracture dominated. Whether the pressure build-up in a cooling brine cell is relieved by inelastic deformation or cracking, the change in the internal structure is likely to play a role in the macroscopic behavior of saline ice. In particular, with the proper temperature history, the phase transformation mechanism can significantly increase the density of dislocations, and can therefore make a significant contribution to the macroscopic compliance of saline ice.