A critical review of the mechanics of polycrystalline ice

We review the developments on the constitutive theories of polar ice both from a viewpoint of mechanics as well as materials science, as it was studied during the last approximately 50 years. First proposals were based on the postulation of ice as a very viscous, non-Newtonian and heat conducting uid. Today's understanding of polar ice sees it as a creeping polycrystal with induced anisotropy and a nontrivial grain-size distribution, both evolving in time. Phenomena related to recrystallization, namely grain rotation, grain-size redistribution by normal and abnormal grain growth, nucleation, polygonization and grain boundary migration have also to be accounted for to obtain a stress constitutive law that may reliably predict ice flow in large ice masses. The main topics on which we focus our efforts are the role of anisotropy and its evolution. We review the models that take the microscopic as well as the macroscopic point of view. Numerical models are also considered. A novel graphical method is proposed for the comprehension of the rules that drive the rotation of the crystallites in a polycrystal, not only for the simple cases of compression and extension but also for the simple shear mode of deformation. Particular emphasis is given to the constitutive theories related to recrystallization phenomena, for which the paper can be considered an introductory overview. The research methods on which all proposed laws are based borrow concepts from the mechanics of solids and materials science but belong also to the class of anisotropic fluids.