Regensburg 2010 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 38: Mechanical Properties III

MM 38.1: Talk

Wednesday, March 24, 2010, 16:30–16:45, H16

Statistical Dislocation Dynamics: Some Comments — •Markus Hütter — Polymer Physics, Department of Materials, ETH Zurich, CH-8093 Zurich, Switzerland

A statistical description of dislocation dynamics is examined from the perspective of nonequilibrium thermodynamics. Particularly, the evolution of the densities of different dislocation types is embedded into a macroscopic model for elasto-viscoplasticity. By this procedure, we discuss in detail the following points.

First, the motion of mobile dislocations is studied in order to formulate a constitutive relation for the plastic strain rate tensor in macroscopic viscoplasticity, also known as the plastic distortion rate tensor. We find a rigid connection between the Peach-Koehler force and the plastic strain rate tensor in terms of a tensorial Orowan equation. The thermodynamic driving force for dislocation motion, and for plastic flow, is identified. Specifically, a clear distinction is made between dislocation interactions and forces on dislocations due to macroscopic stress fields.

Second, we examine some frequently used reaction-type equations for mobile and immobile dislocations to model the ubiquitous strain-hardening. We demonstrate that a certain class of such models is in conflict with thermodynamic principles. The origin of this conflict is identified. Particularly, the absence of the reversal processes for any of the reactions is problematic and sharply contrasts to usual chemical reactions. Possible solutions for restoring the thermodynamic admissibility are discussed.