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Résumé séminaire Tony Rollet

"Hot Spots in Viscoplastic Deformation of Polycrystals"

It is interesting to extract information from simulations of plastic response and 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.  Preliminary results from calculating the response under uniaxial tension on both a synthetic polycrystals and a sample of a nickel alloy 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, distance functions are calculated in order to quantify the relationship between stress localization and microstructural features.  In general, hot spots in stress or dissipation rate occur close to grain boundaries, triple lines and quadruple points.  What is unexpected is that low stress points tend to close microstructural features, which suggests that boundaries can both act as stress risers and can shield. Even in a uniformly oriented polycrystal, the hot spots in effect select the high Taylor factor components.

 

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