A critical assessment of fatigue crack nucleation and growth models for Ni- and Ni,Fe-based superalloys

Modelling of high temperature fatigue crack growth in Inconel 718 under the interaction of fast cyclic loading and hold times at maximum load has been conducted. A model, based on the concept of a damaged zone in front of the crack tip has been applied for three different temperatures, 550, 600 and 650• C, with good agreement for both calibration and validation tests. A statistical evaluation of 22 tests in total was also conducted, which shows that the developed model gives a reasonable scatter factor at a probability of failure of 0.1 %.

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“…[24][25][26][27]; and more recently [28,29]. For some reviews of the area, the reader is referred to, e.g., [30][31][32].…”

mentioning

confidence: 99%

A load history dependent model for fatigue crack propagation in Inconel 718 under hold time conditions

Lundström

Simonsson

Gustafsson

et al. 2014

Engineering Fracture Mechanics

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“…The model by Evans and Saxena [44,48], also discussed in [46], and given by Eq. (8), consists of a number of parameters which will account for most mechanisms believed to affect dwell time damage.…”

Section: Model By Evans and Saxenamentioning

confidence: 99%

“…The model by Saxena [35] (see also [45,46]), has been developed with respect to three crack growth regimes: (1) fully cycle dependent region, (2) intermediate region where both cyclic loads and dwell times affect the total crack growth rate, and finally (3), the fully time dependent region, i.e. the crack growth is only affected by time dependent cracking.…”

Section: Model By Saxenamentioning

confidence: 99%

High Temperature Fatigue Crack Growth in a Ni-based Superalloy : Modelling Including the Interaction of Dwell Times

Storgärds¹

2015

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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

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“…The model by Evans and Saxena [37,39], also discussed in [41], and given by Eq. (9), consists of a number of parameters which will account for most mechanisms believed to affect for hold time damage.…”

Section: Model By Evans and Saxenamentioning

confidence: 99%

“…The model by Saxena [30] (see also [40,41]), has been developed with respect to three crack growth regimes: (1) fully cycle dependent region, (2) intermediate region where both cyclic loads and hold times affect the total crack growth rate, and finally (3), which is the fully time dependent region, i.e. the crack growth is only affected by time dependent cracking.…”

Section: Model By Saxenamentioning

confidence: 99%

Modelling of fatigue crack propagation in Inconel 718 under hold time conditions

Lundström¹

2014

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Cover: Kb-specimen with indicated crack length and damaged zone. The test specimen is subjected to a flight spectrum which is accurately predicted by letting the crack growth rate be dependent on the damaged zone D, which is built up during hold times and consumed during load reversals.Printed by: LiU-Tryck, Linköping, Sweden, 2014 ISBN: 978-91-7519-403-5 ISSN: 0280-7971 Distributed by: Linköping University Department of Management and Engineering SE-581 83, Linköping, Sweden c 2014 Erik Lundström This document was prepared with L A T E X, February 16, 2014 No part of this publication may be reproduced, stored in a retrieval system, or be transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without prior permission of the author. PrefaceThe work presented in this thesis has been carried out at the Division of Solid Mechanics, Linköping University within the project High temperature fatigue crack propagation in nickel-based superalloys, which is a part of the research programme TURBO POWER. The programme is a joint collaboration between the Swedish Energy Agency, Siemens Industrial Turbomachinery AB and GKN Aerospace Engine Systems, from which support and founding are gratefully acknowledged. AbstractIn 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 five appended papers, which describe the work completed so far in the project. v

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A critical assessment of fatigue crack nucleation and growth models for Ni- and Ni,Fe-based superalloys

Cited by 42 publications

References 113 publications

A load history dependent model for fatigue crack propagation in Inconel 718 under hold time conditions

A load history dependent model for fatigue crack propagation in Inconel 718 under hold time conditions

High Temperature Fatigue Crack Growth in a Ni-based Superalloy : Modelling Including the Interaction of Dwell Times

Modelling of fatigue crack propagation in Inconel 718 under hold time conditions

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