Fatigue life enhancement of aircraft structures through bonded crack retarders (BCR)

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dc.contributor.advisorIrving, Phil E.
dc.contributor.advisorZhang, X.
dc.contributor.authorDoucet, Jeremy
dc.date.accessioned2017-01-16T11:58:03Z
dc.date.available2017-01-16T11:58:03Z
dc.date.issued2015-09
dc.description.abstractThe trend in aircraft design is to produce greener airplanes through lighter structures and/or structures with extended life and reduced maintenance. Bonded crack retarders (BCR) are one of the solutions towards that objective. BCR are reinforcing straps bonded to the structure in order to improve the fatigue and damage tolerance properties of the assembly. The aim of this study was to demonstrate that the BCR hybrid technology – beneficial for upper wing cover – could also be applied to lower wing covers. The project also focused on evaluating BCR most important parameters. The fatigue life improvement obtained from BCR was evaluated through a series of coupons and skin-stringer assemblies tested under constant and variable amplitude loading. While the coupon tests demonstrated a life improvement of only 17% under constant amplitude loading, the variable amplitude load tests performed on the skin-stringer assembly demonstrated increased fatigue lives with a factor of 5 and reduced crack growth rates with a factor of 5 to 6. A finite element calculation tool was developed in order to conduct a parametric analysis of BCR geometry through the evaluation of the substrate stress intensity factor in the case of fatigue loading. The main difficulty was to include the interacting mechanism of the substrate lead crack and the disbond of the adhesive layer. The novelty of the approach was to incorporate the fatigue delamination calculation in order to evaluate the fatigue disbond propagation with crack growth. This was embedded in a 3D finite element design tool ReSLIC (Reinforced Structures Life Improvement Calculation). A necessary step to the development of ReSLIC was the analysis of fatigue properties of the adhesive system in order to provide input data for fatigue delamination calculations. To that end, a series of fatigue tests were performed in pure Mode I, pure Mode II and mixed mode with ratios of 25%, 50% and 75% of mode II ... [cont.].en_UK
dc.identifier.urihttp://dspace.lib.cranfield.ac.uk/handle/1826/11279
dc.language.isoenen_UK
dc.publisherCranfield Universityen_UK
dc.rights© Cranfield University, 2015. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright holder.en_UK
dc.subjectLife enhancementen_UK
dc.subjectbonded crack retarderen_UK
dc.subjectbonded strapen_UK
dc.subjectintegral metallic structureen_UK
dc.subjectFEAen_UK
dc.subjectfatigue delaminationen_UK
dc.subjectmixed mode delaminationen_UK
dc.titleFatigue life enhancement of aircraft structures through bonded crack retarders (BCR)en_UK
dc.typeThesis or dissertationen_UK
dc.type.qualificationlevelDoctoralen_UK
dc.type.qualificationnamePhDen_UK

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