A physically based constitutive model for a V-4Cr-4Ti alloy

A constitutive model for low-to-intermediate temperatures, strains, and str ain rates is developed for the program heat of V-4Cr-4Ti. The basic form of the model is derived from more general dislocation-based models of yield s tress and strain hardening. The physically based forms are fit to a databas e derived from tensile tests carried out over a wide range of temperatures and strain rates. Yield and post-yield strain-hardening contributions to th e flow stress are additive. The yield stress has both thermally activated a nd athermal components. The former is described by a two-mechanism activate d dislocation slip model, with contributions that appear to arise from both lattice friction (at lower temperatures) and dislocation pinning by inters titial impurities (at higher temperatures). The yield stress data can be co rrelated using a strain rate-compensated temperature. The model uses a temp erature-weighted average of the two mechanisms. Post-yield strain hardening was found to be approximately athermal. Strain hardening is fit to a two-c omponent modified Voce-type saturating flow stress model. The constitutive model is also used to determine the flow stability limits as estimates of u niform tensile strains. The relatively compact, but mechanism-based, semi-e mpirical model has a number of both fundamental and practical advantages th at are briefly outlined. (C) 2000 Elsevier Science B.V. All rights reserved .