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

Abstract

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