The Role of the Third Deviatoric Stress Invariant in the Creep of Ice

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Analysis of ice deformation data from laboratories and from field measurements on glaciers, coupled with preliminary biaxial creep experiments, suggest that stress configuration (stresses acting in directions other that the direction in which the strain rate is measured) may effect the deformation rate of ice much more than that suggested by Glenn's Flow Law. This study will involve prepared ice in simple shear and in simple shear with simultaneous compression in a cold laboratory at the University of Wisconsin- River Falls. These experiments will test the accuracy of Glen's Flow Law, which assumes independence from the third invariant in describing deformation of ice under biaxial stresses. Results should allow, if necessary, modification of the flow law to a more general form based on both the second and third variants. A second part of this study will involve conducting combined stress tests on glacier ice samples exhibiting a broad range of crystal fabrics and grain sizes to investigate the form of the flow law for anisotropic ice.