Spatiotemporal analysis of Portevin-Le Chatelier deformation bands:: Theory, simulation, and experiment -: art. no. 134109

In many solid solutions plastic deformation becomes unstable at sufficiently high temperature due to dynamic strain aging, i.e., repeated breakaway of dislocations from their solute clouds and recapture by mobile solutes, producing stress serrations in constant strain-rate tests or strain bursts in constant stress-rate tests. The instabilities of this well-known Portevin-Le Chatelier (PLC) effect are closely connected with localization of strain in "PLC deformation bands" with a width of the order of the specimen thickness and sometimes propagating like a soliton along the specimen. In the present work, the nucleation and propagation of PLC deformation bands is studied by means of a multizone laser scanning extensometer, providing information on local strain along the main part of the specimen, in addition to the conventional measurement of stress serrations. This enables one to differentiate clearly between the bands of types A, B, and C, and to explore their ranges of existence at various temperatures, stresses and strain rates as well as transitions between them along the stress-strain curve. The laser extensometer provides independent data on propagation rate, concentrated strain and width of the bands. These experimental data are compared with a theoretical space-time analysis of propagating PLC bands, which explicitly combines a physical description of the kinetics of dynamic strain aging and plastic deformation. This model provides not only analytical predictions for the above band parameters and their dependences on deformation rate and specimen thickness for Type-A PLC bands, but-by considering types B and C as perturbation modes-is also able to explain the observed transitions between the various types of deformation bands. Moreover, the effect of strain hardening on the appearance of PLC strain localization is elucidated. The analytical predictions are validated by numerical simulations of the model and by comparing them to the experimental findings reported here.