Validation of a Constitutive Material Model with Anisothermal Uniaxial and Biaxial Experiments*

Abstract

Abstract The dynamic behaviour of steam turbine components is currently a key issue in terms of the discontinuity in the power supply from regenerative energy systems like wind-mills. These systems call for a combined and flexible use of conventional steam power plants. The influence on fatigue behaviour with superimposed creep on lifetime of large plant components is still unknown. Fatigue loading of such components is induced by temperature transients during start-up and shut-down processes. This requires an anisothermal inspection of the thermo-mechanical fatigue (TMF) loading at design. Hence, a viscoplastic constitutive material model of the Chaboche type was adapted to a 10% Cr forged steel. As a verification of the constitutive material model, uniaxial TMF experiments were performed. These experiments were derived from a temperature cycle on the surface of a turbine rotor during a hot start. The mechanical loading depends on the start temperature and the temperature rate of the start up, and the induced loading of the surface is biaxial. Therefore, a biaxial experiment with variable amplitude loading was also used for the purpose of material model verification. In order to recalculate deformation and to predict lifetime, the constitutive material model was implemented in a FEM calculation. In the present contribution it is shown that the constitutive material model of type Chaboche introduced can be applied to the recalculation of the deformation with an implicit evolution of damage under service-type conditions. Further efforts are necessary to investigate innovative parameter identification procedures and routines for the extrapolation of the inner variables of the constitutive material model under cyclic loading.