Q: Dislocations structures - how far from equilibrium? A: Very close indeed

The combination of Newton's third law, action equals reaction, and of the s econd law of thermodynamics, leads to the LES (Low-Energy Structures) hypot hesis, saying that among all potentially accessible structures, plastic def ormation will generate the one with the lowest free energy. For the particu lar case of dislocation-mediated plastic deformation, this means that, limi ted only by dislocation mobility, availability of slip systems and insignif icant entropy, dislocation structures always approach the lowest possible m echanical energy of the present dislocation population. This insight is a m ost valuable aid in understanding the plastic properties of technological m etals. Among the many aspects of plastic behavior that have been successful ly treated by this means are the evolution of the major dislocation structu re types (Taylor lattices and cell structures), characterizing 'planar-glid e' and 'wavy-glide' metals, respectively, and the resulting differences in workhardening behavior. Further explained are the shape and temperature dep endence of the wavy-glide workhardening curve, the strain rate dependence o f flow stress, thermal recovery of wavy- and planar-glide materials, the tw o observed types of worksoftening, and the shape of the hysteresis curve in constant amplitude fatigue. Lastly, deformation banding does not depend on dislocation behavior and is governed by the LES hypothesis in metals as we ll as in polymers, and presumably also on a geological scale. (C) 2001 Else vier Science B.V. All rights reserved.