Regensburg 2007 – wissenschaftliches Programm

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DY: Fachverband Dynamik und Statistische Physik

DY 7: Statistical physics far from thermal equilibrium

DY 7.6: Vortrag

Montag, 26. März 2007, 15:45–16:00, H5

How microscopic fluctuations give rise to viscoplastic behavior in anisotropic solids — •Markus Hütter and Theo Tervoort — Institute for Polymers, Department of Materials, ETH Zurich, 8093 Zurich, Switzerland.

Temporal coarse-graining in the context of nonequilibrium thermodynamics is used to examine the interrelation between microscopic fluctuations and the viscoplastic behavior in anisotropic solids on the macroscopic scale. As a guideline to complete this task, the general equation for the nonequilibrium reversible-irreversible coupling (GENERIC) framework is used. The state of deformation in elasto-viscoplasticity can be described in terms of the elastic part of the deformation gradient as an internal variable, with its relaxation described by a so-called plastic strain rate tensor. To arrive at a closed set of evolution equations, a constitutive relation for the plastic strain rate tensor is needed. While this is often done phenomenologically on purely macroscopic grounds, we here illustrate a procedure to relate the plastic strain rate tensor to the rapid microscopic fluctuations of the deformation gradient. It is shown how common ansatzes for the plastic strain rate tensor for anisotropic amorphous solids and crystalline solids are obtained by temporal coarse-graining. A major benefit of such a procedure consists in guiding microscopic simulations. In particular, they must be used primarily for the determination of the kinetic coefficients, rather than for extracting the tensorial structure of the plastic strain rate tensor.