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

Rae, Y.; Benaarbia, A.; Hughes, J.; Sun, Wei

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 visco-plastic 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 thermomechanical responses of an industrial gas turbine rotor subjected to in-service 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

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: Jan 29, 2019
• Publicly Available Date: Feb 6, 2020
• 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
• Public URL: https://nottingham-repository.worktribe.com/output/1504148
• Publisher URL: https://www.sciencedirect.com/science/article/pii/S0142112319300313