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On the interply friction of different generations of carbon/epoxy prepreg systems
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.ORCID iD: 0000-0002-6616-2964
2011 (English)In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 42, no 9, 1067-1074 p.Article in journal (Refereed) Published
Abstract [en]

Using pre-stacked material that is formed as a first step in the manufacturing process offers reduced process cycle time for production of complex structural components. The forming is achieved by forcing layers to deform by e.g. intraply deformation and interply slippage, where the latter is the scope of this study. The prepreg-prepreg friction is experimentally determined for four unidirectional carbon/epoxy prepreg systems. The materials differ considering volume fraction of fibres, fibre stiffness and phase of thermoplastic toughener (solved or particles). The study shows large individual differences between the tested materials, where the material systems with particle tougheners seem to obey a boundary lubrication friction, while the other materials show hydrodynamically dominated friction. A large difference between the high and low friction materials, almost a factor of 10, correlates to trends seen in the herein performed surface roughness measurements. Vacuum as well as autoclave consolidated materials are tested.

Place, publisher, year, edition, pages
Elsevier, 2011. Vol. 42, no 9, 1067-1074 p.
Keyword [en]
Prepreg, Carbon fibre, Forming, Surface analysis
National Category
Vehicle Engineering Production Engineering, Human Work Science and Ergonomics Materials Engineering
Research subject
SRA - Production
URN: urn:nbn:se:kth:diva-26091DOI: 10.1016/j.compositesa.2011.04.010ISI: 000293313900001ScopusID: 2-s2.0-79959928978OAI: diva2:369908
XPRES - Initiative for excellence in production research

QC 20110128.  Uppdaterad från submitted till published 20110816.

Available from: 2010-11-12 Created: 2010-11-12 Last updated: 2016-08-11Bibliographically approved
In thesis
1. Forming of stacked unidirectional prepreg materials
Open this publication in new window or tab >>Forming of stacked unidirectional prepreg materials
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

To reduce cost of structural composites, the development of more efficient manufacturing methods is of great interest. An automatic tape layer (ATL) can be used to perform the layup in an efficient way for flat sheets and the second step is by pressure forming the prepreg stack onto a given mould. Sheet forming of thermoset prepreg, also known as hot drape forming, is a promising manufacturing method when combined with automatically stacked laminates. To reach the desired shape, without flaws such as wrinkles and severe fibre angle deviation, knowledge about the forming behaviour of stacked material is important. A simulation of the forming can add to the understanding of mechanisms causing defects and also how to avoid them.

A continuum mechanical finite element approach is used to model the forming of stacked unidirectional prepreg. This with the aim of finding mechanisms causing defects, such as out-of-plane wrinkling and in-plane waviness. Data from experimental characterisation of the materials are required for the constitutive material models. An experimental approach is used to investigate the intraply (within the layer) and interply (between the layers) deformation. The intraply deformation behaviour is investigated by a bias extension test, where resistance to deform and fibre rotation are registered. The interlaminar friction characteristics in the prepreg/prepreg interface are retrieved from tests performed with a specially designed rig. Measurements on the bending stiffness of the prepreg, both transverse to and in the fibre direction, are used in the out-of-plane model.

Different aerospace-grade thermoset prepreg materials are tested and major differences in behaviour are found. Since epoxy is brittle, the resin is toughened by thermoplastics, for some materials in liquid phase and for others by solid particles. These particles seem to influence both the intraply deformation modes and increase the level of friction between layers.

The experimental data from shear, friction and bending tests are used to calibrate the chosen material models. In-plane forming simulations confirm the affect stacking sequence have on the forming behaviour. Full-scale forming simulations on a joggles beam are performed with one of the tested material systems. Two different stacking sequences, with the same amount of fibre in the main directions, are analysed and compared. Both numerical and experimental forming shows that the coupling between layers, due to the interply friction, will affect the forming behaviour and in some cases create wrinkles. Wrinkles can develop both in the plane and out-of-plane, where only the in-plane waviness is present in the performed forming simulations.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. vii, 31 p.
Trita-AVE, ISSN 1651-7660 ; 2012:75
National Category
Composite Science and Engineering
Research subject
SRA - Production
urn:nbn:se:kth:diva-106269 (URN)978-91-7501-558-3 (ISBN)
Public defence
2012-12-18, E2, Lindstedtsvägen 3, KTH, Stockholm, 10:15 (English)
KEKS Kostnadseffektiva kompositstrukturerPRICE Producerbarhet i centrumXPRES
XPRES - Initiative for excellence in production researchTrenOp, Transport Research Environment with Novel Perspectives

QC 20121204

Available from: 2012-12-04 Created: 2012-12-03 Last updated: 2013-04-11Bibliographically approved

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