GA-based multiple objective optimisation for determining viscoplastic constitutive equations for superplastic alloys

A genetic algorithm (GA)-based multiple objective optimisation technique has been developed and used to determine unified viscoplastic constitutive equations for superplastic alloys. It has been found that the GA-based optimisation technique is very effective in solving this kind of problem. The difficulty of choosing correct starting values for the constants in the traditional optimisation techniques has been completely overcome and the GA technique provides a better chance to converge to the global minimum. It has also been found that the hardening due to grain growth plays a very important role in the superplastic deformation of Ti–6Al–4V at 927°C and simplified viscoplastic constitutive equations for the alloy have been determined to accurately model the superplastic flow of the material.