An improved unified viscoplastic model for strain-rate sensitivity in high temperature fatigue
Barrett, Richard A.
O'Donoghue, P. E.
Leen, Sean B.
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Barrett, RA, O Donoghue, PE, Leen, SB (2013) 'An improved unified viscoplastic model for strain-rate sensitivity in high temperature fatigue'. International Journal Of Fatigue, 48 :192-204.
An improved unified cyclic viscoplastic material model for high temperature fatigue of P91 steel is presented. The primary enhancement over existing models is in relation to strain-rate independence of parameters, for accurate interpolation and extrapolation across a range of strain-rates and stress regimes, as relevant to flexible operation of high temperature power generation plant. The model combines a hyperbolic sine constitutive equation with anisothermal cyclic evolution of isotropic and kinematic hardening variables. The material model is developed from a thermodynamic framework and is implemented in multi-axial form within a user material subroutine. The user material subroutine is calibrated and validated for P91 steel across a range of cyclic (isothermal fatigue and thermo-mechanical fatigue) and non-cyclic high temperature loading conditions. A novel method for the identification of the cyclic viscoplastic material parameters is also presented.