Author(s): S. Shyam Sunder; S. Nanthikesan
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Abstract: The interaction between creep deformations and a stationary or growing crack is a fundamental problem in ice mechanics. Knowledge concerning the physical mechanisms governing this interaction is necessary: (1) to establish the conditions under which linear elastic fracture mechanics can be applied in problems ranging from ice-structure interaction to fracture toughness testing; and (2) to predict the ductile-to-brittle transition in the mechanical behavior of ice and, especially, the stability and growth of cracks subjected to crack-tip blunting by creep deformations. This requires a quantitative estimate of the creep zone surrounding a crack-tip, i. e., the zone within which creep strains are greater than the elastic strains. The prediction of the creep zone in previous ice mechanics studies is based on the theory developed by Riedel and Rice (1980) for tensile cracks in creeping solids. This theory is valid for a stationary crack embedded in an isotropic material obeying an elastic, power-law creep model of deformation and for a suddenly applied unifonn far-field tension load that is held constant with time. The deformation of ice at strain-rates ahead of a crack (i. e., 10-6 to 10-2 s-1) is dominated, however, by transient (not steady power-law) creep and the loading, in general, is not instantaneous and constant. This paper presents preliminary results from a comprehensive study which seeks to understand the role of transient creep and related physical mechanisms in predicting the size, shape and time evolution of the inelastic fracture process zone surrounding a crack-tip in polycrystalline ice. The physically-based constitutive theory of Shyam Sunder and Wu 0989a, b) for the multiaxial creep deformation of ice is used in conjunction with a finite element analysis to model the creep-crack interaction problem. The predictions of the numerical model are compared with the analytical solution of Riedel and Rice (1980).
Year: 1992