Seminars & Colloquia Calendar

J.S. Langer

University of California, Santa Barbara

Dislocation Theory: The mysterious disconnect between engineering phenomenology and nonequilibrium statistical physics

It has been known for about a century that the deformability of crystalline solids is determined by the motions of extended line defects known as dislocations. Unfortunately, in the 1950’s, prominent materials theorists incorrectly asserted that the second law of thermodynamics was not relevant to dislocations. As a result, with no foundation in statistical mechanics, dislocation theory has consisted primarily of non-predictive phenomenology, and physicists have mostly lost interest in it.

In this talk, I describe a thermodynamic dislocation theory first published in 2010. It is based on the second law via an effective-temperature analysis. It also assumes that the controlling time scale is given by the thermally activated rate at which entangled dislocations break away from each other. This theory has been found to agree extremely well with a wide range of experimental observations including strain hardening, grain-size effects, shear banding, and – most recently – fracture toughness. Many fundamentally and technologically important phenomena remain to be explored from this physics-based point of view.

The thermodynamic dislocation theory may be illustrative of a wider range of driven systems in which the internal degrees of freedom fall out of thermal equilibrium with each other but behave in ways that are consistent with fundamental statistical principles.