Experimental characterisation and computational modelling of cyclic viscoplastic behaviour of turbine steel

Hughes, J.; Rae, Y.; Benaarbia, A.; Hughes, Jeremy; Sun, W.

Abstract

Fully reversed strain controlled low cycle fatigue and creep-fatigue interaction tests have been performed at ±0.7% strain amplitude and at three different temperatures (400 °C, 500 °C and 600 °C) to investigate the cyclic behaviour of a FV566 martensitic turbine steel. From a material point of view, the hysteresis mechanical responses have demonstrated cyclic hardening at the running-in stage and subsequent, hysteresis cyclic softening during the rest of the material life. The relaxation and energy behaviours have shown a rapid decrease at the very beginning of loading followed by quasi-stabilisation throughout the test. A unified, temperature- and rate dependent viscoplastic model was then developed and implemented into the Abaqus finite element (FE) code through a user defined subroutine (UMAT). The material parameters in the model were determined via an optimisation procedure based on a genetic solver. The multi-axial form of the constitutive model developed was demonstrated by analysing the thermo-mechanical responses of an industrial gas turbine rotor subjected to inservice conditions. A sub-modelling technique was used to optimise the FEA. A 2D global model of the rotor with a 3D sub-model of the second stage of the low pressure turbine were then analysed in turn. The complex transient stress and accumulated plastic strain fields were investigated under realistic thermo-mechanical fatigue loading (start-up and shut-down power plant loads). The sub-model was then used for local analysis leading to identification of potential crack initiation sites for the presented types of blade roots.

Citation

Hughes, J., Rae, Y., Benaarbia, A., Hughes, J., & Sun, W. (2019). Experimental characterisation and computational modelling of cyclic viscoplastic behaviour of turbine steel. International Journal of Fatigue, 124, 581-594. https://doi.org/10.1016/j.ijfatigue.2019.01.022

• Journal Article Type: Article
• Acceptance Date: Jan 29, 2019
• Online Publication Date: Feb 5, 2019
• Publication Date: 2019-07
• Deposit Date: Mar 12, 2019
• Publicly Available Date: Feb 6, 2020
• Journal: International Journal of Fatigue
• Print ISSN: 0142-1123
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 124
• Pages: 581-594
• DOI: https://doi.org/10.1016/j.ijfatigue.2019.01.022
• Keywords: Unified Viscoplasticity; Hysteresis Behaviour; High-Temperature Steel; Turbine Rotor; Finite Element Modelling
• Public URL: https://nottingham-repository.worktribe.com/output/1503685
• Publisher URL: https://www.sciencedirect.com/science/article/pii/S0142112319300313
• Additional Information: This article is maintained by: Elsevier; Article Title: Experimental characterisation and computational modelling of cyclic viscoplastic behaviour of turbine steel; Journal Title: International Journal of Fatigue; CrossRef DOI link to publisher maintained version: https://doi.org/10.1016/j.ijfatigue.2019.01.022; Content Type: article; Copyright: © 2019 Elsevier Ltd. All rights reserved.