Eurofer97 Creep-Fatigue assessment tool for ANSYS APDL and workbench

Abstract

For the design of future fusion reactors the ferritic-martensitic steel Eurofer97 is the main candidate for in-vessel structural application to be able to withstand harsh environment like irradiation and cyclic loading under elevated temperatures. In case of high temperatures, not only fatigue but also creep damage becomes significant and has to be considered. In the past a so called Creep-Fatigue Assessment (CFA) tool has been developed for Finite Element software ANSYS APDL as post-processor within the frame of Engineering Data & Design Integration (EDDI) in EUROfusion. This tool was initially based on the elastic Creep-Fatigue rules of ASME Boiler Pressure Vessel Code (BPVC) Section III Division 1 Subsection NH Appendix T.Nowadays the tool is able to automatically identify the critical region regarding Creep-Fatigue damage in ANSYS APDL and Workbench using local stress, maximum elastic strain range and temperature from elastic thermo-mechanical Finite Element analysis. The use of stress linearization in elastic analysis allows the calculation of a modified equivalent strain range including inelastic effects to finally determine the allowable number of cycles, creep and fatigue damage fraction. For Creep-Fatigue Assessment (CFA) post-processing design fatigue curves, creep stress versus time to rupture curves, monotonic and isochronous stress versus strain curves have been used in the combination with Creep-Fatigue damage interaction diagram to describe the Creep-Fatigue behavior of Eurofer97.As it is well known that Eurofer97 shows cyclic softening, a modified Creep-Fatigue rule has been implemented in CFA tool to improve the underestimation of creep damage. This modified rule uses for calculation of creep damage the stress versus strain and design creep curves of cyclic softened material for some fraction of lifetime and an improved Creep-Fatigue damage interaction diagram of Eurofer97.In cases where the elastic analysis of ASME BPVC is too conservative, inelastic analysis can be used to calculate total strain directly instead of the prediction used in the elastic analysis. This inelastic approach for Creep-Fatigue Assessment is less complicated compared to the elastic route because only few steps according to ASME BPVC are necessary. Nevertheless more efforts for Finite Element simulation including inelastic material behavior are required.In Summary, this CFA tool can be used for fast Creep-Fatigue evaluation. It simply allows the fast identification of Creep-Fatigue damage for a structural component which is made of Eurofer97.