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Deformability of unidirectional prepreg materials
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
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 [en]
prepreg, deformability, carbon composite
National Category
Vehicle Engineering
Identifiers
URN: urn:nbn:se:kth:diva-10681OAI: oai:DiVA.org:kth-10681DiVA: diva2:224958
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
List of papers
1. On the in-plane deformability of cross-plied unidirectional prepreg
Open this publication in new window or tab >>On the in-plane deformability of cross-plied unidirectional prepreg
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
Keyword
prepreg, forming, multi-layer
National Category
Reliability and Maintenance Manufacturing, Surface and Joining Technology Materials Engineering Vehicle Engineering
Research subject
SRA - Production
Identifiers
urn:nbn:se:kth:diva-10677 (URN)10.1177/0021998311412988 (DOI)000302010000006 ()2-s2.0-84859314024 (Scopus ID)
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: 2017-12-13Bibliographically approved
2. On the interply friction of different generations of unidirectional prepreg materials
Open this publication in new window or tab >>On the interply friction of different generations of unidirectional prepreg materials
2008 (English)In: Proceedings of 13th European Conference on Composite Materials (ECCM 13), 2008Conference paper, Published paper (Refereed)
Abstract [en]

With the aim of reducing cost of prepreg composite components, manufacturing methods are developed and refined. An automatic tape laying machine can shorten the process cycle by stacking prepreg flat and thereafter allow for forming into desired shapes. Forming of stacked prepreg requires knowledge about the uncured properties of prepreg, such as viscosity of the matrix, intra- and interply deformation properties. This study focuses on the interply friction, i.e. the friction at the prepreg-prepreg interface, and how this affects the forming. The conclusions presented here show that the difference between prepreg material systems is significant. Further, it is concluded that the prepreg-prepreg friction is governed by a combination of Coulomb and hydrodynamic friction, where different mechanical phenomena dominate depending on the test conditions.

Keyword
prepreg, interply, friction
National Category
Vehicle Engineering Manufacturing, Surface and Joining Technology
Research subject
SRA - Production
Identifiers
urn:nbn:se:kth:diva-10679 (URN)
Conference
ECCM13: 13th European Conference on Composite Materials, 2 - 5 June 2008, Stockholm, Sweden
Projects
Kostnadseffektiva kompositer (KEKS)
Funder
XPRES - Initiative for excellence in production research
Note

QC 20101015

Available from: 2013-01-28 Created: 2009-06-22 Last updated: 2016-08-11Bibliographically approved

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