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Finite element modeling of mechanically fastened composite-aluminum joints in aircraft structures
Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
Saab AB, Linköping, Sweden.
2014 (English)In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 109, 198-210 p.Article in journal (Refereed) Published
Abstract [en]

A three-dimensional, solid finite element model of a composite-aluminum single-lap bolted joint with a countersunk titanium fastener is developed. The model includes progressive damage behavior of the composite and a plasticity model for the metals. The response to static loading is compared to experimental results from the literature. It is shown that the model predicts the initiation and the development of the damage well, up to failure load. The model is used to evaluate the local force-displacement responses of a number of single-lap joints installed in a hybrid composite-aluminum wing-like structure. A structural model is made where the fasteners are represented by two-node connector elements which are assigned the force-displacement characteristics determined by local models. The behavior of the wing box is simulated for bending and twisting loads applied together with an increased temperature and the distribution of fastener forces and the progressive fastener failure is studied. It is shown that the fastener forces caused by the temperature difference are of significant magnitude and should be taken into account in the design of hybrid aircraft structures. It is concluded that, the account of the non-linear response of the joints results in a less conservative load distribution at ultimate failure load.

Place, publisher, year, edition, pages
Elsevier, 2014. Vol. 109, 198-210 p.
Keyword [en]
Bolted joints, Composite-aluminum, Finite element modeling, Hybrid wing structures
National Category
Aerospace Engineering
Identifiers
URN: urn:nbn:se:liu:diva-91893DOI: 10.1016/j.compstruct.2013.10.056ISI: 000331671700020OAI: oai:DiVA.org:liu-91893DiVA: diva2:619501
Available from: 2013-05-03 Created: 2013-05-03 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Strength analysis and modeling of hybrid composite-aluminum aircraft structures
Open this publication in new window or tab >>Strength analysis and modeling of hybrid composite-aluminum aircraft structures
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The current trend in aircraft design is to increase the proportion of fiber composites in the structures. Since many primary parts also are constructed using metals, the number of hybrid metal-composite structures is increasing. Such structures have traditionally often been avoided as an option because of the lack of methodology to handle the mismatch between the material properties. Composite and metal properties differ with respect to: thermal expansion, failure mechanisms, plasticity, sensitivity to load type, fatigue accumulation and scatter, impact resistance and residual strength, anisotropy, environmental sensitivity, density etc. Based on these differences, the materials are subject to different design and certification requirements. The issues that arise in certification of hybrid structures are: thermally induced loads, multiplicity of failure modes, damage tolerance, buckling and permanent deformations, material property scatter, significant load states etc. From the design point of view, it is a challenge to construct a weight optimal hybrid structure with the right material in the right place. With a growing number of hybrid structures, these problems need to be addressed. The purpose of the current research is to assess the strength, durability and thermo-mechanical behavior of a hybrid composite-aluminum wing structure by testing and analysis. The work performed in this thesis focuses on the analysis part of the research and is divided into two parts. In the first part, the theoretical framework and the background are outlined.Significant material properties, aircraft certification aspects and the modeling framework are discussed.In the second part, two papers are appended. In the first paper, the interaction of composite and aluminum, and their requirements profiles,is examined in conceptual studies of the wing structure. The influence of the hybrid structure constitution and requirement profiles on the mass, strength, fatigue durability, stability and thermo-mechanical behavior is considered. Based on the conceptual studies, a hybrid concept to be used in the subsequent structural testing is chosen. The second paper focuses on the virtual testing of the wing structure. In particular, the local behavior of hybrid fastener joints is modeled in detail usingthe finite element method, and the result is then incorporated into a global model using line elements. Damage accumulation and failure behavior of the composite material are given special attention. Computations of progressive fastener failure in the experimental setup are performed. The analysis results indicate the critical features of the hybrid wing structure from static, fatigue, damage tolerance and thermo-mechanical points of view.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2013. 54 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1590
National Category
Aerospace Engineering
Identifiers
urn:nbn:se:liu:diva-91894 (URN)LIU–TEK–LIC–2013:24 (Local ID)978-91-7519-628-2 (ISBN)LIU–TEK–LIC–2013:24 (Archive number)LIU–TEK–LIC–2013:24 (OAI)
Presentation
2013-05-24, Hus A, plan 3, föreläsningssal A35, Campus Valla, Linköping University, Linköping, 10:15 (Swedish)
Opponent
Supervisors
Available from: 2013-05-08 Created: 2013-05-03 Last updated: 2013-05-08Bibliographically approved
2. 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 (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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