On the PLC effect in strain-rate and stress-rate controlled tests-studies by laser scanning extensometry

Applying laser scanning extensometry the development and propagation of Portevin-LeChatelier (PLC) deformation bands is recorded by measuring local strains in up to 22 neighboring 2 mm sections along the specimen length. The quantities characterizing deformation band shape and propagation, i.e. width and concentrated strain in the band, propagation mode (continuous or jerky) and propagation rate, are determined and compared for two tensile testing modes, i.e. constant imposed strain-rate and constant imposed stress-rate. For example the jerky propagation behavior of type B PLC deformation bands observed in strain-rate controlled tests disappears for stress-rate control, where bands move very rapidly over only short distances of the specimen length. The results are compared with predictions of a recent model combining dynamic strain ageing kinetics of dislocations with dislocation dynamics of plastic deformation including work hardening. Common features and differences for the two materials, i.e. short-range ordered Cu-15 at.% Al and Al-3.5 at.% Mg with small precipitates, are discussed in terms of their microstructures. (C) 2004 Elsevier B.V. All rights reserved.