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

Uniform tensile elongation was estimated based on Hart's criterion of m + y greater than or equal to 1 for plastic stability where nz is the strain ra te sensitivity and gamma the strain hardening parameter. These m and gamma are certainly stress- and strain-dependent in nature since they are defined as (partial derivative In sigma/partial derivative In (epsilon) over dot) and (delta In sigma/partial derivative epsilon), respectively, not unique m aterial parameters even in a given deformation condition. In the present pa per, they were descriptively correlated with the deformation parameters bas ed on dislocation dynamics; their values could be obtained from computer si mulation of the true stress-true strain curves. The uniform strains prior t o the local necking were estimated from the simulated deformation parameter s for a mechanically milled Al-1.1at%Mg-1.2at%Cu alloy deformed in tension at various constant fore strain rates (1 x 10(-3) to 5 x 10(0) s(-1)) and t emperatures (523-823 K), and compared with those visually observed using a high speed camera. A reasonable agreement was found between the estimated a nd observed values, indicating the validity of the dislocation dynamics app roach on the basis of a concept of plastic stability proposed by Hart for t he estimation of uniform elongation. (C) 2001 Elsevier Science B.V. All rig hts reserved.