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Fatigue Performance of Additive Manufactured Ti6Al4V in Aerospace Applications
Linköping University, Department of Management and Engineering. Linköping University, Faculty of Science & Engineering.
2017 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Additive Manufacturing (AM) for metals includes is a group of production methodst hat use a layer-by-layer approach to directly manufacture final parts. In recent years, the production rate and material quality of additive manufactured materials have improved rapidly which has gained increased interest from the industry to use AM not only for prototyping, but for serial production. AM offers a greater design freedom, compared to conventional production methods, which allows for parts with new innovative design. This is very attractive to the aerospace industry, in which parts could be designed to have reduced weight and improved performance contributing to reduced fuel consumption, increased payload and extended flight range. There are, however, challenges yet to solve before the potential of AM could be fully utilized in aerospace applications. One of the major challenges is how to deal with the poor fatigue behaviour of AM material with rough as-built surface.

The aim of this thesis is to increase the knowledge of how AM can be used for high performance industrial parts by investigating the fatigue behaviour of the titanium alloy Ti6Al4V produced with different AM processes. Foremost, the intention is to improve the understanding of how rough as-built AM surfaces in combination with AM built geometrical notches affects the fatigue properties.This was done by performing constant amplitude fatigue testing to compare different combinations of AM material produced by Electron Beam Melting(EBM) and Laser Sintering (LS) with machined or rough as-built surfaces with or without geometrical notches and Hot Isostatic Pressing (HIP) treatment. Furthermore, the material response can be different between constant amplitude and variable amplitude fatigue loading due to effects of overloads and local plastic deformations. The results from constant amplitude testing were used to predict the fatigue life for variable amplitude loading by cumulative damage approach and these predictions were then verified by experimental variable amplitude testing.

The constant amplitude fatigue strength of material with rough as-built surfaces was found to be 65-75 % lower, compared to conventional wrought bar, in which HIP treatments had neglectable influence on the fatigue strength. Furthermore, the fatigue life predictions with cumulative damage calculations showed good agreement with the experimental results which indicates that a cumulative damage approach can be used, at least for a tensile dominated load sequences, to predict the fatigue behaviour of additive manufactured Ti6Al4V.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2017. , 50 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1775
National Category
Other Materials Engineering Manufacturing, Surface and Joining Technology Applied Mechanics Composite Science and Engineering Tribology
Identifiers
URN: urn:nbn:se:liu:diva-137233DOI: 10.3384/lic.diva-137233ISBN: 9789176855386 (print)OAI: oai:DiVA.org:liu-137233DiVA: diva2:1094203
Presentation
2017-06-02, ACAS, A-huset, Campus Valla, Linköping, 10:15 (Swedish)
Opponent
Supervisors
Available from: 2017-05-09 Created: 2017-05-09 Last updated: 2017-05-11Bibliographically approved
List of papers
1. Fatigue Behaviour of Notched Additive Manufactured Ti6Al4V with As-built Surfaces
Open this publication in new window or tab >>Fatigue Behaviour of Notched Additive Manufactured Ti6Al4V with As-built Surfaces
2017 (English)In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, no 101, 51-60 p.Article in journal (Refereed) Published
Abstract [en]

Additive manufacturing (AM) allows the manufacturer to produce parts with complex geometries that are difficult to produce with conventional production methods. Generally, AM is considered to have great potential for the aerospace industry by contributing to reduced weight and lower costs. There are a number of challenges to be solved before AM can be fully utilized in the aerospace industry, and the understanding of fatigue behaviour is one of the major challenges. Although the fatigue properties of flat additive manufactured specimens with rough as-built surfaces already have been widely studied, in practice, few aerospace components have a simple flat geometry with no corners or radii that would act as stress concentrations. Therefore, the combined effect on fatigue life of a rough as-built surface and a geometrical notch needs to be established. In this study, the fatigue properties of both laser sintered and electron beam melted Ti6Al4V have been investigated and a combined effect of a rough as-built surface and a geometrical notch has been determined. In addition, hot isostatic pressing was found to have no impact on fatigue life for rough as-built surfaces. These findings can be directly applied to predict fatigue behaviour of an AM industrial component.

Place, publisher, year, edition, pages
Elsevier, 2017
Keyword
Additive manufacturing, Fatigue, Ti6Al4V, Stress concentration, Fatigue notch factor
National Category
Materials Engineering
Identifiers
urn:nbn:se:liu:diva-137163 (URN)10.1016/j.ijfatigue.2017.04.009 (DOI)000403635300007 ()
Note

Funding agences: Saab AB; Swedish Foundation for Strategic Research; European commission, through the Clean Sky 2 programme

Available from: 2017-05-08 Created: 2017-05-08 Last updated: 2017-07-07Bibliographically approved

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