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Ultra Thick Laminates for Compact Load Introduction Fittings
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Composites are increasingly often used for thick and compact structures with the clear aim to reduce the overall weight and cost of an aircraft. But classic applications of composites are thinner structures with limited out of plane loads. Analysis and test methods are therefore commonly developed and used for thinner structures and neglect the special challenges involved with thicker laminates. In addition composites are increasingly becoming interesting for fittings and joints since the surrounding structures are either built or being developed in composites a well. Using metallic fitting and joints can cause additional thermal stresses and /or corrosion due to the material mix of composites and metals. Due to the enlarged field of application for composites, there is an increasing demand for suitable analysis, test and manufacturing methods. Compact and highly loaded composite structures are prone to be subjected to high and multidirectional loads. This causes an atypical load situation for composites, which usually are subjected to plane loads to best exploit the strength of the fibers. Due to the orthotropic nature of the material a large amount of design variables are introduced. The design of any composite part is highly manufacturing driven, meaning that the final shape is determined by manufacturing capabilities. Thick composites provide a cost effective alternative and can generate a distinct weight benefit over standard metallic components and hence will a play a significant role in future aircraft developments. Analysis, testing and manufacturing methods have to be developed and adapted for that purpose. A reliable analysis is only possible if accurate 3D material properties are available. Analysis capabilities have to be assessed using empirical test data in order to judge the applicability. The presented work has its emphasis on the analysis and testing of structural components manufactured in thick composites. The generated data from a comprehensive manufacturing and test program is also used as basis for a cost and weight study under the assumption of a highly automized serial production. The results further underline the potential of thick composites.  In a first approach, standard 2D finite element methods are used for a topology investigation. In order to fully capture the behavior of the material 3D methods are quickly implemented. An extensive test program with full scale samples and coupons is used to improve and evolve the analysis. An open mold manufacturing cycle minimizes tooling costs and provides optimum flexibility for frequent design changes. A strong link between the analysis, the manufacturing and the design is maintained throughout the developments in order to generate a material suitable design solution. Although the ultimate goal is to manufacture a specific component, the topics are approached as generic as possible in order to provide a basis for future studies with similar boundary conditions. Despite the fact that the material creates countless design variables, an affordable approach for the analysis of thick composite structures is provided using standard 3D composite brick elements. The initial problem of missing reliable 3D material properties is counteracted with tests of full scale sub- components and modified short beam shear tests. A new cure cycle for thick laminates is presented and analyzed to assess process induced stresses and deformations. A large landing gear fitting component is designed and manufactured and can be regarded as an excellent demonstrator of ultra thick composites. With a maximum wall thickness of 90mm, the component provides a weight reduction of 18% and a cost benefit of approximately 20% compared to the metallic counterpart. The potential of composites applied to a compact and highly loaded fitting is demonstrated and suitable analysis methods are established. A need for future tests to provide reliable and generic 3D material properties is identified. To provide a weight and cost benefit it is crucial to find a design topology suitable for composites.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology , 2011. , viii, 28 p.
Series
Trita-AVE, ISSN 1651-7660 ; 2011:77
National Category
Aerospace Engineering
Identifiers
URN: urn:nbn:se:kth:diva-46730ISBN: 978-91-7501-156-1 (print)OAI: oai:DiVA.org:kth-46730DiVA: diva2:454092
Public defence
2011-11-25, F3, Lindstedsvägen 26, KTH, Stockholm, 13:15 (English)
Opponent
Supervisors
Projects
ALCAS
Funder
TrenOp, Transport Research Environment with Novel Perspectives
Note
QC 20111114Available from: 2011-11-14 Created: 2011-11-04 Last updated: 2012-06-12Bibliographically approved
List of papers
1. Testing and analysis of ultra thick composites
Open this publication in new window or tab >>Testing and analysis of ultra thick composites
2010 (English)In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 41, no 4, 326-336 p.Article in journal (Refereed) Published
Abstract [en]

For the development of a composite main landing gear fitting in carbon fiber reinforced plastics the behavior and performance of Ultra Thick Laminate components is investigated. Material thicknesses exceeds 60 mm. For the purpose of validation a test program is arranged using T-cross sections subjected to multiple load cases. The components are manufactured entirely with non crimped fabrics (NCF) using an adapted open mould manufacturing process. In addition to these T-Sections large full scale subcomponents of the entire fitting are manufactured and tested. As main topic of this paper standard FE methods are investigated and validated for thick structures using the generated test results. Due to the presence of transverse shear and normal stresses a 3D modeling approach is chosen. Transverse shear and normal stresses are indentified as main failure cause and failure is mainly initiated in the curved regions. Solid composite brick elements offer an efficient way to model thick structures. These are incapable of calculating accurate shear stresses on a ply level; usable results are however achieved by discretisation of the component with multiple elements over thickness. In addition stress gradients in the failure region are small; stress variations on a ply level are minimal. Out of plane material properties are not available and initial assumptions are made. Material correction factors (degradation) are introduced and discussed.

Place, publisher, year, edition, pages
Elsevier, 2010
Keyword
Carbon carbon composites, Finite element analysis (FEA), Ultra thick laminates
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-27551 (URN)10.1016/j.compositesb.2009.12.004 (DOI)000278253800008 ()2-s2.0-77951298968 (Scopus ID)
Note

QC 20101216

Available from: 2010-12-16 Created: 2010-12-13 Last updated: 2017-12-11Bibliographically approved
2. Three-dimensional stress and progressive failure analysis of ultra thick laminates and experimental validation
Open this publication in new window or tab >>Three-dimensional stress and progressive failure analysis of ultra thick laminates and experimental validation
Show others...
2011 (English)In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 93, no 5, 1394-1403 p.Article in journal (Refereed) Published
Abstract [en]

Test methods and analysis capabilities for fibre reinforced composites are generally limited to thin laminates. However, extending the range of application of composite materials to thick laminates is essential for a multitude of possible composite structures. This paper presents an adapted three-point bending test for a new quasi isotropic stacking sequence for non crimped fabrics for the application in ultra thick laminates (UTL). In addition, numerical simulation capabilities for thick laminates using a multiscale analysis are shown. The three-point bending test setup is developed to examine the failure behaviour of 30-60 mm thick coupons. The presented numerical analysis features a ply based mesh, stacked continuum elements as well as a multiscale approach with meso scale unit cells in order to refine initial assumptions for 3D material properties. Initial stress calculations are performed on macro level using material properties from 2D tests. Extending the analysis by a multiscale approach, material properties are generated on meso level using unit cells models. Progressive failure is subsequently modelled on macro level, using the previously obtained material properties and the Juhasz failure criterion. The failure load is compared to experimental findings.

Place, publisher, year, edition, pages
Elsevier, 2011
Keyword
Ultra thick laminates, Multiscale analysis, Composites, Progressive failure
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-47446 (URN)10.1016/j.compstruct.2010.11.009 (DOI)000287110700008 ()2-s2.0-79955479912 (Scopus ID)
Note

QC 20111109

Available from: 2011-11-09 Created: 2011-11-09 Last updated: 2017-12-08Bibliographically approved
3. Simulation of Process Induced Deformations in Ultra-thick Laminates Manufactured with Vacuum Assisted Process
Open this publication in new window or tab >>Simulation of Process Induced Deformations in Ultra-thick Laminates Manufactured with Vacuum Assisted Process
(English)Manuscript (preprint) (Other academic)
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-47648 (URN)
Note
QS 2011Available from: 2011-11-11 Created: 2011-11-11 Last updated: 2011-11-14Bibliographically approved
4. Analysis and Manufacturing of Ultra Thick Laminates for Future Aircraft Applications
Open this publication in new window or tab >>Analysis and Manufacturing of Ultra Thick Laminates for Future Aircraft Applications
2008 (English)In: ECCM-13, 2008, 2008Conference paper, Published paper (Other academic)
Abstract [en]

Compact and highly loaded composite components experience extensive transverse shear stress concentrations in areas of load introduction and curved sections. Standard 3D multilayered composite brick elements are employed to analyze UTL. For the purpose of validation several full-scale test components with T-cross section have been manufactured with thicknesses ranging from 60-90mm. In a first approach single non interactive failure criteria have been used due to the uncertainty of out of plane material properties. Despite the fact that the used element type provides a simple mean of modeling and analyzing UTL, it is found that the element formulation strictly limits the accuracy of transverse shear stress prediction. The quadratic or even linear approximation of in plane displacements does not account for the irregular distribution in thickness direction [1]. Global deformations of the geometry can however be calculated with good results. Most failure modes experienced, are found to be dominated by transverse shear or out of plane peeling stresses. Particularly in the region of load introduction. For the analysis of the final landing gear fitting material restricted correction factors are introduced. In addition to the T-Sections, large so called ‘Double Corners’ are tested in both in plane and out of plane direction to develop effective countermeasures for premature failure modes, such as throat washers and load distribution plates. The utilized modified VAP cycle has significant benefits compared to closed mould processes, such as reduced tooling costs and high flexibility. For curved UTL sections spring back effects and preform compression rates are considered to improve laminate quality.

Keyword
Ultra thick laminates, open mould manufacturing, vacuum assisted process, multilayered composite brick element
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-47651 (URN)
Conference
European Conference on Composite Materials ECCM-13, Stockholm, Sweden, 2008
Note

QC 20111111

Available from: 2011-11-11 Created: 2011-11-11 Last updated: 2015-08-28Bibliographically approved
5. Cost and Weight Analysis of Ultra Thick Laminates for a Compact Landing Gear Fitting
Open this publication in new window or tab >>Cost and Weight Analysis of Ultra Thick Laminates for a Compact Landing Gear Fitting
2011 (English)In: SICOMP 2011, 2011Conference paper, Published paper (Other academic)
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-47652 (URN)
Note
QC 20111111Available from: 2011-11-11 Created: 2011-11-11 Last updated: 2011-11-14Bibliographically approved

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