Hot Spots in Viscoplastic Deformation of Polycrystals

Anthony Rollett
Carnegie-Mellon University

Deformation of polycrystalline materials, whether elastic or plastic, is akin to deformation of a composite in which each grain has different properties by virtue of its anisotropic response to loading. It is interesting to extract information from simulations of both thermoelastic and viscoplastic response for various types of deformation, and to relate the peaks in stress, for example, to the microstructural features. Do the “hot spots” concentrate at or near grain boundaries, for example? Given a 3D representation of a polycrystalline material, various methods are available to calculate its properties. An alternative to the standard finite element method is to model the mechanical properties on the image itself using a spectral method based on Fast Fourier transforms (FFT ). Preliminary results from calculating the response under stress free boundary conditions for synthetic polycrystals and a sample of a tin thin film are given. Stress concentrations and their relationship to grain boundaries are of particular interest, for example, since they can determine the location of rapid damage accumulation. Accordingly, (Euclidean) distance functions are calculated in order to quantify the relationship between stress localization and microstructural features. In general, hot spots in stress or elastic energy density occur close to grain boundaries, triple lines and quadruple points . We focus on results from simulations of viscoplastic deformation to large strains with comparisons to experimental results from EBSD and High Energy Diffraction Microscopy (HEDM) .

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