Surrogate Modeling of Viscoplasticity in Steels: Application to Thermal, Irradiation Creep and Transient Loading in HT-9 Cladding

The use of structural metals in extreme environments relies both on the characterization of the mechanical response and microstructure changes in service and on modeling predictions. Data scarcity creates a need for predictive constitutive models that can be used in regimes outside calibration domains. While crystal plasticity models can be applied to non-monotonic loads and complex environments, their computational cost typically prohibits use at the level of an engineering structure. As an alternative, the present study introduces a surrogate constitutive model derived from crystal-plasticity predictions of the mechanical response of HT9 subjected to irradiation, stresses and temperatures. The surrogate law is then tested in the cases of uniaxial straining, stress cycling, thermal cycling and thermal ramping. Finally, using this constitutive relationship, finite element simulations of a pressurized tube subjected to a stress and thermal transients are performed and analyzed.