Uniform tensile elongation obtained from experiment and its estimation using dislocation dynamics parameters

Uniform tensile elongation was estimated based on Hartʹs criterion of m+γ≥1 for plastic stability where m is the strain rate sensitivity and γ the strain hardening parameter. These m and γ are certainly stress- and strain-dependent in nature since they are defined as (∂ ln σ/∂ ln ε̇) and (∂ ln σ/∂ε), respectively, not unique material parameters even in a given deformation condition. In the present paper, they were descriptively correlated with the deformation parameters based on dislocation dynamics; their values could be obtained from computer simulation of the true stress–true strain curves. The uniform strains prior to the local necking were estimated from the simulated deformation parameters for a mechanically milled Al–1.1at%Mg–1.2at%Cu alloy deformed in tension at various constant true strain rates (1×10−3 to 5×100 s−1) and temperatures (523–823 K), and compared with those visually observed using a high speed camera. A reasonable agreement was found between the estimated and observed values, indicating the validity of the dislocation dynamics approach on the basis of a concept of plastic stability proposed by Hart for the estimation of uniform elongation.