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An experimental study of mechanisms behind wrinkle development during forming of composite laminates
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.ORCID iD: 0000-0002-6616-2964
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2013 (English)In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 50, 54-64 p.Article in journal (Refereed) Published
Abstract [en]

A general problem when forming quasi-isotropic, multilayer unidirectional (UD) prepreg over a double curved geometry is out-of-plane wrinkling. The presented study aims to show the existence of compression in the laminate in a recess area that is globally under tension during forming. Further it aims to investigate the influence of compression on the out-of-plane wrinkle development.

An experimental study is performed with pre-stacked UD prepreg on a forming tool with varying cross section. Investigated parameters include lay-up sequence, prepreg ply thickness, inter-ply friction and prepreg ply impregnation. Experimental evaluation is performed on the out-of-plane defect height, type, location and number. Further, measurements are performed on the outer-ply deformation in the z-direction and inside the formed component using Micro CT. The study show that compression is to some degree always developed during forming of a recess area but that the lay-up sequence has a dominant effect on the wrinkling development.

Place, publisher, year, edition, pages
Elsevier, 2013. Vol. 50, 54-64 p.
Keyword [en]
A. Carbon fiber, A. Laminates, E. Forming, E. Prepreg
National Category
Vehicle Engineering
Research subject
SRA - Production
Identifiers
URN: urn:nbn:se:kth:diva-116488DOI: 10.1016/j.compositesa.2013.03.013ISI: 000320149000007Scopus ID: 2-s2.0-84876567357OAI: oai:DiVA.org:kth-116488DiVA: diva2:589911
Funder
XPRES - Initiative for excellence in production research
Note

QC 20130719

Available from: 2013-01-21 Created: 2013-01-21 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Towards defect free forming of multi-stacked composite aerospace components using tailored interlayer properties
Open this publication in new window or tab >>Towards defect free forming of multi-stacked composite aerospace components using tailored interlayer properties
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Use of lightweight materials is an important part of reduction of fuel consumption by commercial aircraft. A considerable number of structural aircraft parts are therefore built of thin layers of epoxy pre-impregnated carbon fibres stacked to laminates. Manufacturing these by hand is costly and different methods of automation have therefore been developed. One cost-effective way of manufacturing is Automated Tape Lay-up of flat stacks followed by a Hot Drape Forming operation. A well-known problem in the industry within forming is fibre wrinkling, which can cause a serious strength knock down. The focus of this thesis has therefore been on understanding how and why wrinkles develop during forming of multi-layer stacks and, based on this, investigate different methods for process and material improvements.

The work presented initially investigates the dependency between stacking sequence and wrinkle development. It is shown that wrinkle free forming can be obtained by changing the fibre stacking order. In the following investigation it is shown that the wrinkles cannot be entirely eliminated by local stiffening of the critical layers. In a, related study it is shown that different kinds of wrinkles develops during forming; wrinkles may be either due to global buckling of the entire lay-up or local compression of single layers. Global buckling is due to excessive material. Local compression occurs as the material shear during forming.

The work presented leads to an understanding of the importance of making the beneficial neighbouring fibre layers interact during forming. One way to connect neighbouring layers is to tailor the interlayer properties. A study is presented that shows how local manipulation of interlayer properties may steer the multi-layered material into a different deformation mechanisms. The manipulation in this thesis is performed using Multi Wall Carbon Nano Tubes, thermoplastic veils or consolidation of thermoplastic toughener particle interlayers.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. 30 p.
Series
TRITA-AVE, ISSN 1651-7660 ; 2016:19
Keyword
Carbon Fibre, Composites, Prepreg, Forming
National Category
Aerospace Engineering
Research subject
Aerospace Engineering
Identifiers
urn:nbn:se:kth:diva-185694 (URN)978-91-7595-950-4 (ISBN)
Public defence
2016-06-01, Sal F3, Lindstedtsvägen 26, Stockholm, 10:15 (English)
Opponent
Supervisors
Funder
VINNOVA, NFFP5 2010-01257VINNOVA, NFFP6 2013-01220VINNOVA, GF Demo 2012-01031VINNOVA, GF Demo 2013-04667
Note

QC 20160425

Available from: 2016-04-25 Created: 2016-04-25 Last updated: 2016-05-16Bibliographically approved

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Hallander, PerÅkermo, Malin

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