Material characterization of Inconel 718 from free bulging test at high temperature

Macroscopic superplastic behavior of metallic or non metallic materials is usually represented by the strain-rate sensitivity, and it can be determined by tensile tests in uniaxial stress state and bulging tests in multi axial stress state, which is the actual hot forming process. And macroscopic behavior of Non-SPF grade materials could be described in a similar way as that of superplastic materials, including strain hardening, cavity and so on. In this study, the material characterization of non-SPF grade Inconel 718 has been carried out to determine the material parameters for flow stress throughout free bulging test under constant temperature. The measured height of bulged plate during the test was used for estimation of strain-rate sensitivity, strain-hardening index and cavity volume fraction with the help of numerical analysis. The bulged height obtained from the simulation showed good agreement with the experimental findings. The effects of strain-hardening and cavity volume fraction factor for flow stress were also compared.