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High temperature fatigue crack growth behaviour of Inconel 718 under hold time and overload conditions
Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
2013 (English)In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 48, 178-186 p.Article in journal (Refereed) Published
Abstract [en]

Inconel 718 is a frequently used material for gas turbine applications at temperatures up to 650°C. For such components, the main load cycle is typically defined by the start-up and shut-down of the engine. In this main loading cycle, hold times at high temperature are commonly present in critical components. These high temperature hold times may greatly increase the fatigue crack growth rate with respect to the number of cycles unless other beneficial factors such as for example initial overloads are present. The latter can be caused by abnormal service conditions but can also occur on a more regular basis and are then typically observed in components with strong thermal transients during engine start-up. In this paper, focus has been placed on the effect of overloads on the hold time fatigue crack growth behaviour and its subsequent description. More specifically, crack propagation in Inconel 718 has been studied at the temperatures 550°C and 650°C with and without an overload at the start of the cycle. The effect of initial overloads was found to be substantial. A simple model for describing the effect of these loading conditions has also been developed based on the concept of the damaged zone, present around the crack tip. Irregular crack fronts and unbroken ligaments left on the fracture surfaces seen in complementary microscopy studies seem to support this approach. Furthermore, the stress state in front of a crack tip in a 2D model was investigated both with and without an initial overload. The results were related to the observed crack growth retardation behaviour found in the material testing.

Place, publisher, year, edition, pages
Elsevier , 2013. Vol. 48, 178-186 p.
Keyword [en]
Nickel-base superalloys, fatigue crack propagation, Inconel 718, hold times, grain boundary embrittlement, crack propagation modelling, Finite Element modelling
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-85931DOI: 10.1016/j.ijfatigue.2012.10.018ISI: 000315617500020OAI: oai:DiVA.org:liu-85931DiVA: diva2:573854
Available from: 2013-03-13 Created: 2012-12-03 Last updated: 2017-12-07Bibliographically approved
In thesis
1. High temperature fatigue crack propagation behaviour of Inconel 718
Open this publication in new window or tab >>High temperature fatigue crack propagation behaviour of Inconel 718
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The overall objective of this work has been to develop and evaluate tools for designing against fatigue in gas turbine applications, with special focus on the nickel-based superalloy Inconel 718. The fatigue crack propagation behaviour under high temperature hold times has been studied. Firstly, the main fatigue crack propagation phenomena have been investigated with the aim of setting up a basis for fatigue crack propagation modelling. Secondly, modelling of the observed behaviour has been performed. Finally, the constitutive behaviour of the material has been studied, where focus has been placed on trying to describe the mean stress relaxation and initial softening of the material under intermediate temperatures.

This thesis is divided into two parts. The first part describes the general framework, including basic observed fatigue crack propagation behaviour of the material when subjected to hold times at high temperature as well as a background for the constitutive modelling of mean stress relaxation. This framework is then used in the second part, which consists of the seven included papers.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2013. 37 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1487
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-85934 (URN)978-91-7519-750-0 (ISBN)
Public defence
2013-02-01, C3, Hus C, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2012-12-03 Created: 2012-12-03 Last updated: 2012-12-10Bibliographically approved
2. Modelling of fatigue crack propagation in Inconel 718 under hold time conditions
Open this publication in new window or tab >>Modelling of fatigue crack propagation in Inconel 718 under hold time conditions
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis an investigation and modelling of the fatigue crack propagation in the nickel based superalloy Inconel 718, with a special emphasis on the effect of hold times, is presented. The modelling work has been concentrated on describing the hold time fatigue crack propagation by using the concept of a damaged zone in front of the crack tip, which is believed to have a lowered resistance against crack propagation.

The modelling framework is built on physically motivated parameters, which are all easy to calibrate through one specially designed test type. Later evaluation through many experimental tests has also shown that the model is capable, within reasonable scatter level to predict, the hold time fatigue crack propagation for many different temperatures and loading conditions. Further evaluation of a complex flight spectrum, with the incorporation of crack closure within the model, was also predicted with a satisfying result.

This thesis is divided into two parts. First, a background and a somewhat deeper discussion of the modelling of fatigue crack growth under hold time conditions is presented. The second part consists of ve appended papers, which describe the work completed so far in the project.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. 48 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1645
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-104814 (URN)10.3384/lic.diva-104814 (DOI)978-91-7519-403-5 (ISBN)
Presentation
2014-03-21, A34, Hus A, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2014-02-27 Created: 2014-02-27 Last updated: 2014-03-14Bibliographically approved
3. High Temperature Fatigue Crack Growth in a Ni-based Superalloy: Modelling Including the Interaction of Dwell Times
Open this publication in new window or tab >>High Temperature Fatigue Crack Growth in a Ni-based Superalloy: Modelling Including the Interaction of Dwell Times
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Safe life of gas turbines is always of major concern for manufacturers in order to ensure passenger safety and stable continuous power output. An increasing amount of resources have been put into research and development to assure that all safety aspects are covered in the design of new turbines and to ensure that enough frequent service intervals are scheduled to avoid complications. Many of these issues require good knowledge of material properties and of how to use these in the design process. Some of these relate to fatigue which is of major concern in all parts of a development programme. However, while some fatigue problems have been extensively studied, some have not. One example is crack growth with influence of dwell times at elevated temperature in combination with cyclic loading. Such loading conditions have been shown to give a different cracking behaviour compared to rapid cyclic loading, increasing the growth rate significantly with respect to the number of load cycles. Improved models for predicting this behaviour is therefore of major interest for gas turbine manufacturers, and could substantially increase the reliability. As a result, more research is needed in order  solve these problems.

The work presented in this dissertation has focused on how to predict life under the above-mentioned circumstances. The materials used in high temperature gas turbine applications are often nickel-based superalloys, and in this work the most common one, Inconel 718, has been studied. Mechanical experiments have been performed under operation like conditions in order to receive material data for the subsequent modelling work. The modelling approach was chosen such that the underlying physics of the dwell time cracking have been incorporated on a phenomenological basis, creating a model which can be physically motivated as well as used for industrial applications. The main feature of the modelling work has been to track material damage which is received from dwell times, how this interacts with cyclic loading and how it affects the crack growth rate, thus creating a load history dependent model.

The outcome of this work has resulted in a model which is both easy to use and which has shown to give good correlation to available experimental data. Key components such as calibration for cheap and easy parameter determination, validation on complex engine spectra loadings, three dimensional crack growth, overload influences, material scatter, thermo-mechanical fatigue crack growth and the impact of high cycle fatigue loadings, are all covered in the presented work, both as experimental findings and as continuous development of the modelling concept.

The dissertation consists of two parts. In the first an introduction with the theory and background to crack growth with dwell times is given, while the second part consists of 10 papers.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2015. 51 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1681
National Category
Mechanical Engineering Applied Mechanics Materials Engineering
Identifiers
urn:nbn:se:liu:diva-121012 (URN)10.3384/diss.diva-121012 (DOI)978-91-7519-034-1 (ISBN)
Public defence
2015-09-11, C3, Hus C, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2015-09-02 Created: 2015-09-02 Last updated: 2015-09-02Bibliographically approved

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Gustafsson, DavidLundström, Erik

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