Identification of inelastic material parameters for modified 9Cr–1Mo steel applicable to the plastic and viscoplastic constitutive equations

In this paper, the material parameters of plastic and viscoplastic constitutive equations for modified 9Cr–1Mo steel are developed for various isothermal conditions to support inelastic analysis for a sodium-cooled fast reactor. To do this, the material parameters related with the elastoplastic behaviour are identified with uniaxial cyclic test data by performing computer simulations, which use the combined Chaboche model including the kinematic hardening rule and the isotropic softening rule. The viscous parameters are identified from uniaxial stress relaxation test data through computer simulations with the pre-determined elastoplastic material parameters. Sensitivity studies are performed for the material parameters to investigate cyclic inelastic behaviour and stress relaxation during a hold time. From the comparison between the tests and the simulations, it is expected that the identified material parameters of the plastic and viscoplastic constitutive equations can accurately express the material characteristics of modified 9Cr–1Mo steel sufficiently well to be used for inelastic analysis.