Mechanism-based constitutive equations for superplastic forming of TA15 with equiaxed fine grain structure

In this study, a set of mechanism-based viscoplastic constitutive equations has been established to predict the viscoplastic flow of TA15 alloy sheets in superplastic forming (SPF) processes. Internal variables are introduced in these constitutive equations to represent individual physical features of the material with equiaxed fine grain structure, such as dislocation density, isotropic hardening, recrystallization and dynamic recovery. 13 material constants in the constitutive equations have been determined from experimental data at a range of temperatures and strain rates. A gradient based optimisation method was applied for the calibration of the equations. Good agreement between the computational and experimental results has been obtained. These newly determined constitutive equations can be used for product and process design through superplastic forming processes.