Assessment of modelling methodologies for prediction of high-temperature creep-fatigue behaviour of Alloy 617. (November 2020)

• Record Type: Journal Article
• Authors: Douzian, G.; Muránsky, O.; Kruzic, J.J.; Wright, R.N.; Payten, W.
• Is Part Of: International journal of pressure vessels and piping. Volume 187(2020)
• Publication Date: 2020-11
• Subjects: Creep-fatigue -- Creep -- Fatigue -- High-temperature -- Alloy 617; Pressure vessels -- Periodicals; Pipe -- Periodicals; Récipients sous pression -- Périodiques; Tuyaux -- Périodiques; Pipe; Pressure vessels; Periodicals; 681.76041
• DOI: 10.1016/j.ijpvp.2020.104150
• Languages: English
• ISSNs: 0308-0161

Abstract

Abstract: This study aims to assess the accuracy of various modelling methodologies in predicting creep-fatigue damage ( d c f ) and cycles-to-crack-initiation ( N i ) of Alloy 617 at 850 °C and 950 °C. In the decoupled methodologies, four creep damage models were employed: (i) the time fraction (TF), (ii) ductility exhaustion (DE), (iii) stress-modified ductility exhaustion (SMDE), and (iv) strain-energy density (SED), to capture the creep damage ( d c ) contribution to the overall creep-fatigue damage ( d c f ), while fatigue damage ( d f ) contribution was always calculated using the simple "average" approach. Furthermore, we employed Holmström's integrated ϕ model, which combines the d c f into a single parameter without a need of separate assessment of creep damage ( d c ) and fatigue damage ( d f ). The results show that there is no significant difference between the integrated ϕ model and decoupled creep-fatigue methodologies when the creep damage models are calibrated to creep-fatigue (CF) data. However, it is shown that the accuracy of the creep-fatigue damage ( d c f ) predictions using the decoupled approach gets significantly worse when the creep damage models are calibrated against independent creep-rupture (CR) data. It is further shown that when using DE, SMDE, SED creep damage models, the d c f predictions are arranged by strain range, suggesting that these models are better at capturing strain range variations rather than temperature changes. Based on the obtained results it is recommended that any of the employed creep damage models are all suitable for coupling with the "average" fatigue damage model when capturing the creep-fatigue behaviour of Alloy 617, as long as the employed creep damage model is calibrated directly to the experimental creep-fatigue (CF) data. Highlights: Creep-fatigue of Alloy 617 at 850 °C and 950 °C was predicted using various models. Calibration of models' parameters to the creep-fatigue experimental data improves the accuracy. Tested models perform to a similar level of accuracy when calibrated to creep-fatigue data.