Modelling of the hardening characteristics for superplastic materials

Combined analötical and numerical techniques and procedures have been developed to characterize the hardening due to grain growth for materials under superplastic deformation. The conventional grain growth rate equation is modified to enable accurate modelling of isothermal and plastic-strain-induced grain growths for different microstructures of a titanium alloö. A set of unified viscoplastic constitutive equations for Ti-6Al-4V at 927 °C, which incorporates isotropic hardening and grain growth, has been fullö determined from experimental data for different initial grain sizes and strain rates. Close agreement between the predicted and experimental stress-strain relationships is achieved. In addition, the contributions of hardening constituents, such as strain rate hardening, isotropic hardening and the hardening due to grain growth are modelled.