A combined critical plane and critical distance approach for predicting fatigue crack initiation in notched single-crystal superalloy components

Leidermark, Daniel; Moverare, Johan; Simonsson, Kjell; Sjöström, Sören

doi:10.1016/j.ijfatigue.2011.05.009

Cited by 58 publications

(31 citation statements)

References 23 publications

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“…In this study, the TCD was applied by considering not only the linearelastic 21,22 but also the elasto-plastic 32 formalisation of this theory. It is worth recalling here also that Leidermark et al 33 have recently shown that the critical plane method applied along with the critical distance concept can successfully be used to estimate lifetime of notched single-crystal superalloy MD2 subjected, at 500°C, to uniaxial fatigue loading. It is worth recalling here also that Leidermark et al 33 have recently shown that the critical plane method applied along with the critical distance concept can successfully be used to estimate lifetime of notched single-crystal superalloy MD2 subjected, at 500°C, to uniaxial fatigue loading.…”

Section: Introductionmentioning

confidence: 93%

The linear‐elastic Theory of Critical Distances to estimate high‐cycle fatigue strength of notched metallic materials at elevated temperatures

Louks

Susmel

2014

Fatigue Fract Eng Mat Struct

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This paper investigates the accuracy of the linear‐elastic Theory of Critical Distances (TCD) in estimating high‐cycle fatigue strength of notched metallic materials experiencing elevated temperatures during in‐service operations. The TCD postulates that the fatigue damage extent can be estimated by directly post‐processing the entire linear‐elastic stress field acting on the material in the vicinity of the crack initiation locations. The key feature of this theory is that the high‐cycle fatigue assessment is based on a scale length parameter that is assumed to be a material property. The accuracy of this design method was checked against a number of experimental results generated, under axial loading, by testing, at 250 °C, notched specimens of carbon steel C45. To further investigate the reliability of the TCD, its accuracy was also checked via several data taken from the literature, these experimental results being generated by testing notched samples of Inconel 718 at 500 °C as well as notched specimens of directionally solidified superalloy DZ125 at 850 °C. This validation exercise allowed us to prove that the linear‐elastic TCD is successful in estimating high‐cycle fatigue strength of notched metallic materials exposed to elevated temperature, resulting in estimates falling within an error interval of ±20%. Such a high level of accuracy suggests that, in situations of practical interest, reliable high‐cycle fatigue assessment can be performed without the need for taking into account those non‐linearities characterising the mechanical behaviour of metallic materials at high temperature, the used critical distance being still a material property whose value does not depend on the sharpness of the notch being designed.

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Section: Introductionmentioning

confidence: 93%

The linear‐elastic Theory of Critical Distances to estimate high‐cycle fatigue strength of notched metallic materials at elevated temperatures

Louks

Susmel

2014

Fatigue Fract Eng Mat Struct

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“…For crack initiation, the critical distance must vary between these extremes. It has been suggested that this can be accounted for by a cycle dependent critical distance [4,5] = (5) where is the critical distance and and are fitting parameters. However, Equation 5 is somewhat inconvenient to use for life predictions where is unknown.…”

Section: An Equation For the Critical Distancementioning

confidence: 99%

“…Furthermore, a significant part of the total life is still made up by the crack initiation phase and, consequently, the total life is largely influenced by the stresses at the notch (the number of cycles to initiation, on average, constituted ~60 % of the total life in the current fatigue tests). Since the theory of critical distances could be expected to account for the notch influence on the crack initiation life for low cycle fatigue [5], it is believed that it could also be used for explaining differences in the total life.…”

Section: An Equation For the Critical Distancementioning

confidence: 99%

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Evaluation of notch effects in low cycle fatigue of alloy 718 using critical distances

et al. 2018

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Abstract. Gas turbine disks contain many notch-like features acting as stress raisers. The fatigue life based on the notch root stress may be overly conservative as the steep stress gradient in front of the notch may give rise to so-called notch support. In the current work, the theory of critical distances was applied to the prediction of the total fatigue life of low cycle fatigued, notched specimens made from alloy 718. The fatigue tests were performed at 450 °C and 550 °C. It was found that, for lives shorter than 5000-10000 cycles, the notched specimens had longer lives than would have been expected based on the notch root strain. For lives longer than 5000-10000 cycles, there were no notch support. The life prediction for notched specimens could be significantly improved by basing the prediction on the strain chosen some distance from the notch (the critical distance). An expression for calculating the critical distance based on the notch root strain was suggested.

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“…Previous research has shown that the deformation in single-crystal materials is often localized to a number of crystallographic deformation bands and that cracks follow these bands more easily [12]. Thus, the cracks cannot be expected to follow the conventional Mode I Stress Intensity Factor (SIF) dependency (i.e.…”

Section: Zusammenfassungmentioning

confidence: 99%

Aspects of Crack Growth in Single-Crystal Nickel-Base Superalloys

Busse¹

2017

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Linköping, December 2017Cover: Front: Anisotropic stress response of an FE-simulation of an uncracked DCT specimen. Back: Stress response at the crack tip of an FE-simulation of a cracked DCT specimen.Printed by: LiU-Tryck, Linköping, Sweden, 2017 ISBN: 978-91-7685-395-5 ISSN: 0280-7971 Distributed by: Linköping University Division of Solid Mechanics SE-581 83 Linköping, Sweden © 2017 Christian Busse This document was prepared with L A T E X, November 14, 2017 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 Licentiate of Engineering thesis has been generated at the Division of Solid Mechanics at Linköping Universtiy and is part of the research project KME-702. The research has been funded by the Swedish Energy Agency and Siemens Industrial Turbomachinery AB through the Research Consortium of Materials Technology for Thermal Energy Processes, the support of which is greatly acknowledged. The research project concerns the fields of mechanical testing, microstructure investigations and modelling. This variety gave me the opportunity to learn something new in many different fields almost every day.This Furthermore, I would like to thank my friend and fellow PhD student J-L, who helped me with many fruitful discussions and makes the PhD life more joyful.Finally, I would like to thank Nathalie, who, even though we had to part ways, has always supported me and was always there for me. In a way, I am where I am today because of you. I will always be grateful for that and I will never forget you. Thank you! AbstractThis Licentiate of Engineering thesis is a product of the results generated in the research project KME-702, which comprises modelling, microstructure investigations and material testing of cast nickel-base superalloys.The main objective of this work is to model the fatigue crack propagation behaviour in single-crystal nickel-base superalloys. To achieve this, the influence of the crystal orientations on the cracking behaviour is assessed. The results show that the crystal orientation is strongly affecting the material response and must be accounted for. Furthermore, a linear elastic crack driving force parameter suitable for describing crystallographic cracking has been developed. This parameter is based on resolved anisotropic stress intensity factors and is able to predict the correct crystallographic cracking plane after a transition from a Mode I crack. Finally, a method to account for inelastic deformations in a linear elastic fracture mechanics context was investigated. A residual stress field is extracted from an uncracked finite-element model with a perfectly plastic material model and superimposed on the stress field from the cracked model with a linear elastic material model to account for the inelastic deformations during the determination of the crack driving force. The modellin...

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A combined critical plane and critical distance approach for predicting fatigue crack initiation in notched single-crystal superalloy components

Cited by 58 publications

References 23 publications

The linear‐elastic Theory of Critical Distances to estimate high‐cycle fatigue strength of notched metallic materials at elevated temperatures

The linear‐elastic Theory of Critical Distances to estimate high‐cycle fatigue strength of notched metallic materials at elevated temperatures

Evaluation of notch effects in low cycle fatigue of alloy 718 using critical distances

Aspects of Crack Growth in Single-Crystal Nickel-Base Superalloys

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