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Fatigue bearing failure of CFRP composite in bolted joints exposed to biaxial variable amplitude loading at elevated temperature
Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering. Saab AB, SE-58188 Linkoping, Sweden.
Saab AB, SE-58188 Linkoping, Sweden.
Swedish Def Research Agency, Sweden.
Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
2016 (English)In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 142, 71-77 p.Article in journal (Refereed) Published
Abstract [en]

Hybrid structures than contain composite-aluminium interfaces tend to develop internal loads at elevated temperatures. In long bolted joints, the thermally induced bolt loads are superimposed onto the mechanically applied load and can induce a biaxial bearing load state. This paper presents an experimental and numerical study of the bearing fatigue failure of carbon-epoxy laminate specimens, exposed to uniaxial and biaxial variable amplitude loading at 90C. A specifically designed experimental rig was used, where both the mechanical and the thermally induced bolt loads were applied by means of mechanical load actuators. A fatigue model based on the kinetic theory of fracture for polymers, which was previously implemented for constant amplitude loading, is expanded to account for the variable amplitude load history. The results suggest that the biaxial loading gives a longer fatigue life than the uniaxial loading for the same maximum peak resultant force. This result can be utilized as a conservative dimensioning strategy by designing biaxially loaded joints in terms of maximum peak resultant bearing load using uniaxial fatigue data.

Place, publisher, year, edition, pages
Elsevier, 2016. Vol. 142, 71-77 p.
Keyword [en]
Carbon-epoxy, Thermally induced load, Fatigue bearing failure, Variable amplitude loading
National Category
Composite Science and Engineering
Identifiers
URN: urn:nbn:se:liu:diva-122420DOI: 10.1016/j.compstruct.2016.01.064ISI: 000372691300008OAI: oai:DiVA.org:liu-122420DiVA: diva2:866311
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Funding agencies:  Swedish Armed Forces; Swedish Defence Materiel Administration; Swedish Governmental Agency for Innovation Systems

Available from: 2015-11-02 Created: 2015-11-02 Last updated: 2016-05-02Bibliographically approved
In thesis
1. Static and Fatigue Failure of Bolted Joints in Hybrid Composite-Aluminium Aircraft Structures
Open this publication in new window or tab >>Static and Fatigue Failure of Bolted Joints in Hybrid Composite-Aluminium Aircraft Structures
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The use of fibre composites in the design of load carrying aircraft structures has been increasing over the last few decades. At the same time, aluminium alloys are still present in many structural parts, which has led to an increase of the number of hybrid composite-aluminium structures. Often, these materials are joined at their interface by bolted connections. Due to their different response to thermal, mechanical and environmental impact, the composite and the aluminium alloy parts are subject to different design and certification practices and are therefore considered separately.The current methodologies used in the aircraft industry lack well-developed methods to account for the effects of the mismatch of material properties at the interface.One such effect is the thermally induced load which arises at elevated temperature due to the different thermal expansion properties of the constituent materials. With a growing number of hybrid structures, these matters need to be addressed. 

The rapid growth of computational power and development of simulation tools in recent years have made it possible to evaluate the material and structural response of hybrid structures without having to entirely rely on complex and expensive testing procedures.However, as the failure process of composite materials is not entirely understood, further research efforts are needed in order to develop reliable material models for the existing simulation tools.

The work presented in this dissertation involves modelling and testing of bolted joints in hybrid composite-aluminium structures.The main focus is directed towards understanding the failure behaviour of the composite material under static and fatigue loading, and how to include this behaviour in large scale models of a typical bolted airframe structure in an efficient way. In addition to that, the influence of thermally induced loads on the strength and fatigue life is evaluated in order to establish a design strategy that can be used in the industrial context.

The dissertation is divided into two parts. In the first one, the background and the theory are presented while the second one consists of five scientific papers.

Place, publisher, year, edition, pages
Linköping University Electronic Press, 2015. 53 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1706
Keyword
Hybrid structures; Composites; Bearing failure; Bolted joints
National Category
Aerospace Engineering
Identifiers
urn:nbn:se:liu:diva-122349 (URN)10.3384/diss.diva-122349 (DOI)978-91-7685-942-1 (print) (ISBN)
Public defence
2015-12-03, C3, Hus C, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2015-11-02 Created: 2015-10-29 Last updated: 2015-11-02Bibliographically approved

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