Creep constitutive model considerations for high-temperature finite element numerical simulations

Abstract

Finite element modelling is increasingly used as an integral part of creep analyses for the integrity assessment of high-temperature structures. An important consideration in such finite element simulations is the constitutive model used to represent the creep strain response of the component material as a function of temperature, stress and time. There are a variety of creep models which can be chosen by the analyst for implementation in finite element codes. In this study, five different creep models have been fitted to a set of experimental uniaxial creep curves for a 1%CrMoV turbine rotor steel at 550 °C. Subsequently, the derived constitutive equations have been implemented in finite element model representations of a series of fracture mechanics compact tension specimens manufactured from the same heat of the steel and loaded at the same temperature. The outcome clearly demonstrates the potential sensitivity of high-temperature numerical analyses of structures to the type of creep model adopted, and to the scope of the experimental data from which the model is derived. This is shown by comparing the load point displacement records from a number of compact tension specimen creep crack incubation tests with the results of finite element simulations employing the different creep deformation models. FE calculated steady-state creep stress/strain distributions ahead of the notches of compact tension specimens can also exhibit a strong sensitivity to the type of creep model adopted. Prior benchmarking the effectiveness of finite element simulation procedures for critical high-temperature components with the selected material creep model equation is therefore strongly recommended.