A general hereditary multimechanism-based deformation model with application to the viscoelastoplastic response of titanium alloys

The formulation of a general model for the hereditary behavior of materials, in the viscoelastic and viscoplastic regimes, is presented. In this, we utilize the complete-potential structure as a general framework, together with the notion of strain- and stress- partitioning in terms of separate contributions of several submechanisms (viscoelastic and viscoplastic) to the thermodynamic functions (stored energy and dissipation). Detailed numerical treatments are given for both (i) the implicit integration algorithm for the governing flow and evolutionary rate equations of the model, and (ii) the automated parameter-estimation methodology (using the software code COMPARE) for characterization. For illustration, a specific form of the model presented is characterized for the TIMETAL 21S material using a very comprehensive test matrix, including creep, relaxation, constant strain-rate tension tests, etc. Discussion of these correlations tests, together with comparisons to several other experimental results, are given to assess the performance and predictive capabilities of the present model as well as the effectiveness and practical utility of the algorithms proposed.