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A modified compliance method for fatigue crack propagation applied on a single edge notch specimen
Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering. Siemens Ind Turbomachinery AB, Sweden.
Siemens Ind Turbomachinery AB, Sweden.
Siemens Ind Turbomachinery AB, Sweden.
Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
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2016 (English)In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 92, p. 61-70Article in journal (Refereed) Published
Abstract [en]

Crack length measurements with high accuracy are often difficult to achieve during fatigue crack propagation testing under non-isothermal conditions. In this work a modified approach to the compliance method defined in e.g. ASTM E647 is described, which is better suited for high loads, varying temperatures and for taking the scatter in Youngs modulus into account. A numerical finite element study is performed for a single edge notch specimen, to investigate the influence of initiation locations on the accuracy of the method. The change in cracked area versus change in stiffness for three different cases are numerically shown to collapse to one curve, i.e. the result is not significantly affected by how the crack is initiated. The numerical study is compared to results from two experiments using different materials, with heat tinting during the tests for extracting snapshots of the crack fronts. A good agreement between the experiments and the numerical study is shown. A new compliance curve and a new geometry function for the stress intensity factor is proposed for the single edge notch specimen. (C) 2016 Elsevier Ltd. All rights reserved.

Place, publisher, year, edition, pages
London: ELSEVIER SCI LTD , 2016. Vol. 92, p. 61-70
Keywords [en]
Fatigue testing; Nickel-based superalloy; Thermo-mechanical fatigue; Compliance method; Crack length
National Category
Applied Mechanics
Identifiers
URN: urn:nbn:se:liu:diva-132041DOI: 10.1016/j.ijfatigue.2016.06.023ISI: 000383930200007OAI: oai:DiVA.org:liu-132041DiVA, id: diva2:1038580
Note

Funding Agencies|Siemens Industrial Turbomachinery AB, Finspang, Sweden

Available from: 2016-10-19 Created: 2016-10-17 Last updated: 2024-04-12Bibliographically approved
In thesis
1. A ΔJ approach for nonlinear fatigue crack propagation: Experimental and numerical investigation of a ductile superalloy
Open this publication in new window or tab >>A ΔJ approach for nonlinear fatigue crack propagation: Experimental and numerical investigation of a ductile superalloy
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This dissertation is a product of an academic-industrial collaboration between the Division of Solid Mechanics at Linköping University and Siemens Energy AB. The focus is on enhancing the design optimisation procedures for high-temperature components in industrial gas turbines (IGT). The research is centred around the behaviour of the nickelbased high-temperature superalloy Haynes 230 under service-like conditions with predominant thermal loads. The aim is to improve fatigue crack propagation life predictions for nonlinear conditions.

The research findings validate the thermal ageing fatigue effects on Haynes 230 as seen in existing literature, especially on constitutive properties and crack initiation. Additionally, it was observed that thermal ageing has a minor effect on the crack growth rate up to 600 °C, which can be managed by updating the crack driving force with thermally aged properties.

The project mainly focused on nonlinear crack propagation at isothermal and thermomechanical fatigue conditions. A new method for crack length description, using a modified compliance method, is introduced. This method simplifies and enhances the accuracy of crack length measurements and has become an established method for evaluating the single edge notch specimen used in the project under thermo-mechanical fatigue conditions.

The nonlinear fatigue parameter ΔJ was incorporated into both Finite element method (FEM) computations and test evaluations, revealing linear trends with crack growth rates in loglog. The research highlights the crucial role of crack opening in establishing a correlation between ΔJ and crack growth rate. It was also concluded that the linear fatigue fracture parameter ΔK tends to underestimate the crack growth behaviour, resulting in non-conservative outcomes if the elasto-plastic stresses from the tests are considered.

Lastly, a constitutive description of Haynes 230, based on the Ohno-Wang theory, under negligible viscoplastic effects, and an extension of the cycle jumping procedure that takes into account the significant hardening between the initial and midlife stages of the material, is presented. By this the notched geometry in 3D could be simulated with satisfying accuracy.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2024. p. 66
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 2381
Keywords
ΔJ, Cyclic J-integral, Fatigue testing, Nickel-based superalloy, Thermo-mechanical fatigue, Elasto-plastic fracture mechanics
National Category
Applied Mechanics
Identifiers
urn:nbn:se:liu:diva-202442 (URN)9789180755924 (ISBN)9789180755931 (ISBN)
Public defence
2024-05-17, C3, C Building, Campus Valla, Linköping, 10:15
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Note

Funding agency: Siemens Energy AB

Available from: 2024-04-12 Created: 2024-04-12 Last updated: 2024-04-12Bibliographically approved

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