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High temperature fatigue crack propagation behaviour of Inconel 718
Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
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: urn:nbn:se:liu:diva-85934ISBN: 978-91-7519-750-0 (print)OAI: oai:DiVA.org:liu-85934DiVA: diva2:573867
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
List of papers
1. Fatigue crack growth behaviour of Inconel 718 with high temperature hold times
Open this publication in new window or tab >>Fatigue crack growth behaviour of Inconel 718 with high temperature hold times
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2010 (English)In: Procedia Engineering, ISSN 1877-7058, E-ISSN 1877-7058, Vol. 2, no 1, 1095-1104 p.Article in journal (Refereed) Published
Abstract [en]

In this work, fatigue crack growth measurements have been made on center-cracked tension specimens of Inconel 718, where the focus has been to observe the effect of high temperature hold times on the fatigue crack growth behaviour of the material. The material testing has been done at three different temperatures, namely 450 degrees C, 550 degrees C and 650 degrees C. All testing were done in an isothermal LCF context with a standard test method for measuring the fatigue crack growth rates.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2010
Keyword
nickel-base superalloys; fatigue crack propagation; Inconel 718
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-58352 (URN)10.1016/j.proeng.2010.03.118 (DOI)000278762900116 ()
Available from: 2010-08-13 Created: 2010-08-11 Last updated: 2017-12-12Bibliographically approved
2. Modeling of the Constitutive Behavior of Inconel 718 at Intermediate Temperatures
Open this publication in new window or tab >>Modeling of the Constitutive Behavior of Inconel 718 at Intermediate Temperatures
2011 (English)In: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 133, 094501-1-094501-4 p.Article in journal (Refereed) Published
Abstract [en]

Turbine disks are of large importance to turbine designers as theyare exposed to hot environment and subjected to high loads. Inorder to analyze such components with respect to fatigue crackinitiation, the work generally starts with a rigorous analysis of thefirst few cycles, during which an important stress redistributionwill always take place in an inelastic structure. In this work, thenonlinear kinematic hardening law by Ohno and Wang (1998,“Constitutive Modeling of Cyclic Plasticity With Emphasis onRatchetting,” Int. J. Mech. Sci., 40, pp. 251–261) has been used incombination with an isotropic softening law for describing theinitial stress-strain distribution for strain controlled uniaxial testsof the material Inconel 718. Focus has been placed on finding asimple model with few material parameters and to describe theinitial softening and the comparatively small mean stress relaxationobserved during the material testing. The simulation resultsobtained by using the model fit the experimental resultswell.

Place, publisher, year, edition, pages
ASME, 2011
National Category
Applied Mechanics
Identifiers
urn:nbn:se:liu:diva-68035 (URN)10.1115/1.4002913 (DOI)000290494800020 ()
Available from: 2011-05-06 Created: 2011-05-06 Last updated: 2017-12-11
3. Influence of high temperature hold times on the fatigue crack propagation in Inconel 718
Open this publication in new window or tab >>Influence of high temperature hold times on the fatigue crack propagation in Inconel 718
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2011 (English)In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 33, no 11, 1461-1469 p.Article in journal (Refereed) Published
Abstract [en]

High temperature fatigue crack growth in Inconel 718 has been studied at the temperatures 450 degrees C, 500 degrees C, 550 degrees C and 650 degrees C. The tests were conducted both without hold times and with hold times of different lengths and with a mix of both. Focus has been on quantifying the effect the hold time has upon the crack growth rate and how much it damages the material. Furthermore, it has been investigated how this damage influences the actual cracking behavior, i.e. where in the loading cycle the damage contributes most to the crack growth. This damage is related to the concept of a damaged zone in front of the crack tip. The size of the damaged zone has been derived from the tests and a microscopy study to confirm the findings has also been carried out. It is found that the concept of a damaged zone can be a successful explanatory model for the observed crack growth behavior under high temperature hold time.

Place, publisher, year, edition, pages
Elsevier, 2011
Keyword
Nickel-base superalloys, Fatigue crack propagation, Inconel 718, Hold times, Grain boundary embrittlement
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-70317 (URN)10.1016/j.ijfatigue.2011.05.011 (DOI)000293991000006 ()
Note
Funding Agencies|Swedish Energy Agency||Siemens Industrial Turbomachinery AB||Volvo Aero Corporation||Royal Institute of Technology||Available from: 2011-09-02 Created: 2011-09-02 Last updated: 2017-12-08
4. Hold-time effect on the thermo-mechanical fatigue crack growth behaviour of Inconel 718
Open this publication in new window or tab >>Hold-time effect on the thermo-mechanical fatigue crack growth behaviour of Inconel 718
2011 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 528, no 29-30, 8660-8670 p.Article in journal (Refereed) Published
Abstract [en]

In-phase TMF crack growth testing with different lengths of the hold time at the maximum temperature of 550 °C has been conducted on Inconel 718 specimens. Focus has been on establishing a method for TMF crack growth testing and investigating the effect of high temperature hold times on the TMF crack growth of the material. The tests are compared to isothermal crack propagation tests and show good correlation. It is concluded that the controlling effect of the crack growth is an embrittlement of the material. This embrittlement is related to the concept of a damaged zone active in front of the crack tip. The size of this damaged zone will control the crack propagation rate and therefore it does not matter if the load is cycled under isothermal or TMF conditions.

Place, publisher, year, edition, pages
Elsevier, 2011
Keyword
TMF, crack growth
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:liu:diva-71304 (URN)10.1016/j.msea.2011.08.027 (DOI)000296676800046 ()
Note
Funding agencies|Swedish Energy Agency||Siemens Industrial Turbomachinery AB||Volvo Aero Corporation||Royal Institute of Technology||Available from: 2011-10-11 Created: 2011-10-11 Last updated: 2017-12-08
5. Fatigue Crack Growth behaviour of Inconel 718 - the Concept of a Damaged Zone Caused by High Temperature Hold Times
Open this publication in new window or tab >>Fatigue Crack Growth behaviour of Inconel 718 - the Concept of a Damaged Zone Caused by High Temperature Hold Times
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2011 (English)In: Procedia Engineering, ISSN 1877-7058, E-ISSN 1877-7058, Vol. 10, 2821-2826 p.Article in journal (Refereed) Published
Abstract [en]

Fatigue crack growth testing of Inconel 718 has been carried out at the temperatures 550 °C and 650 °C. The tests were conducted using a mix of hold times and pure cyclic loading, referred to as block tests. From the test results, the existence of an embrittled volume or damaged zone in the vicinity of the crack tip has been revealed. It has been found that the evolution of this damaged zone can be sufficiently well described using a power law function with an exponent n = 0.25.

Place, publisher, year, edition, pages
Elsevier, 2011
Keyword
nickel base superalloys, fatigue crack propagation, Inconel 718, hold times, grain boundary embrittlement
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-70552 (URN)10.1016/j.proeng.2011.04.469 (DOI)
Available from: 2011-09-12 Created: 2011-09-12 Last updated: 2017-12-08
6. High temperature fatigue crack growth behaviour of Inconel 718 under hold time and overload conditions
Open this publication in new window or tab >>High temperature fatigue crack growth behaviour of Inconel 718 under hold time and overload conditions
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
Keyword
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:nbn:se:liu:diva-85931 (URN)10.1016/j.ijfatigue.2012.10.018 (DOI)000315617500020 ()
Available from: 2013-03-13 Created: 2012-12-03 Last updated: 2017-12-07Bibliographically approved
7. Modelling of high temperature fatigue crack growth in Inconel 718 under hold time conditions
Open this publication in new window or tab >>Modelling of high temperature fatigue crack growth in Inconel 718 under hold time conditions
2013 (English)In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 52, 124-130 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. The main load cycle for such components is typically defined by the start-up and shut-down of the engine. It generally includes hold times at high temperatures, which have been found to have a potential for greatly increasing the fatigue crack growth rate with respect to the number of load cycles. However, these effects may be totally or partly cancelled by other load features, such as overloads or blocks of continuous cyclic loading, and the actual crack propagation rate will therefore depend on the totality of features encompassed by the load cycle. It has previously been shown that the increased crack growth rate found in hold time experiments can be associated with a damage evolution, where the latter is not only responsible for the rapid intergranular crack propagation during the actual hold times, but also for the increased crack growth during the load reversals. In this paper, modelling of the hold time fatigue crack growth behaviour of Inconel 718 has been carried out, using the concept of a damaged zone as the basis for the treatment. With this conceptually simple and partly novel approach, it is shown that good agreement with experimental results can be found.

Place, publisher, year, edition, pages
Elsevier, 2013
Keyword
Nickel-base superalloys, fatigue crack propagation, Inconel 718, hold times, grain boundary embrittlement, crack propagation modelling
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-85933 (URN)10.1016/j.ijfatigue.2013.03.004 (DOI)000318831300013 ()
Available from: 2012-12-03 Created: 2012-12-03 Last updated: 2017-12-07Bibliographically approved

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