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On the in-plane deformability of cross-plied unidirectional prepreg
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
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.ORCID iD: 0000-0002-5235-1000
2011 (English)In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 46, no 8, 929-939 p.Article in journal (Refereed) Published
Abstract [en]

The work presented herein aims to characterise the in-plane properties of cross-plied unidirectional prepreg using the bias extension method. The study is focusing on carbon fibre/epoxy material systems and testing is performed at elevated temperatures to enhance formability. Using digital image correlation (DIC), the specimen deformation and fibre rotation is captured during tests. The study shows that the cross-plied unidirectional material deforms at different characteristic length scales as deformation continues: first seemingly continuous and later in form of bands. Further, the different type of prepreg materials investigated behaves differently; for one type the pin-jointed net theory fit well, enabling simple estimation of resulting fibre angle, while for another not. Different loading speed, temperatures and layup methods are investigated in order to pin-point its influence on the deformability.

Place, publisher, year, edition, pages
Sage Publications, 2011. Vol. 46, no 8, 929-939 p.
Keyword [en]
prepreg, forming, multi-layer
National Category
Reliability and Maintenance Manufacturing, Surface and Joining Technology Materials Engineering Vehicle Engineering
Research subject
SRA - Production
Identifiers
URN: urn:nbn:se:kth:diva-10677DOI: 10.1177/0021998311412988ISI: 000302010000006Scopus ID: 2-s2.0-84859314024OAI: oai:DiVA.org:kth-10677DiVA: diva2:224714
Projects
Kostnadseffektiva kompositstrukturer (KEKS)NFFP Price
Funder
XPRES - Initiative for excellence in production research
Note

QC 20120424

Available from: 2013-01-25 Created: 2009-06-22 Last updated: 2016-08-11Bibliographically approved
In thesis
1. Deformability of unidirectional prepreg materials
Open this publication in new window or tab >>Deformability of unidirectional prepreg materials
2009 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

 To reduce cost of structural composites the development of more efficient manufacturing methods is of great interest. Sheet forming of thermoset prepreg, also known as hot drape forming, has been a promising manufacturing method for decades. An automatic tape layer (ATL) can be used to perform the lay-up in an efficient way. The flatly stacked unidirectional prepreg forms a sheet to be formed over a given mould. Knowledge about the materials forming behaviour is important to reach the required shape without flaws, such as wrinkles.

An experimental approach is developed to investigate the intra- (within the layer) and interply deformation. The intraply deformation properties are registered by the use of a bias-extension test and a digital image correlation (DIC) equipment. To measure the interlaminar (between the layers) friction in the prepreg/prepreg interface a specialized rig is designed and built.

The two tested materials are Cycom® HTA/977-2 from Cytec and HexPly® T700/M21 from Hexel, which are examples of the second and third generation of carbon fibre/epoxy prepreg. Where M21 includes craze stoppers in form of thermoplastic particles, the 977-2 has the same function but in melted stage. These particles seem to influence both the intraply deformation modes and increase the level of friction between layers.

The results from the bias-extension test was compared with the theory of pin-jointed net (PJN) and it was found that M21 behaves accordingly. The measured rotation for 977-2 is less than the theoretical, this due to slippage. The rate of deformation seems to have an influence not only on the load level, but also in the mode of deformation. Both for the interlaminar and intraply deformation the resistance to motion were much larger for M21 than 977-2.

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. 25 p.
Series
Trita-AVE, ISSN 1651-7660 ; 2009:32
Keyword
prepreg, deformability, carbon composite
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-10681 (URN)
Presentation
2009-06-12, H1, Teknikringen 33, KTH, Stockholm, 13:15 (Swedish)
Opponent
Supervisors
Projects
KEKS (kostnadseffektiva kompositer)
Available from: 2009-06-24 Created: 2009-06-23 Last updated: 2012-09-19Bibliographically approved
2. 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.
Series
Trita-AVE, ISSN 1651-7660 ; 2012:75
National Category
Composite Science and Engineering
Research subject
SRA - Production
Identifiers
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)
Opponent
Supervisors
Projects
KEKS Kostnadseffektiva kompositstrukturerPRICE Producerbarhet i centrumXPRES
Funder
XPRES - Initiative for excellence in production researchTrenOp, Transport Research Environment with Novel Perspectives
Note

QC 20121204

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

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