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Compressive failure of glass fibre NCF composites
Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
2007 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Compressive failure of polymer matrix compos ites is very much controlled by material heterogeneity (e.g. fibre waviness and gaps) and out-of-plane loadings (e.g. impact), and to enable design of robust and trustworthy components it is important to understand how different heterogeneity and loadings affect the governing failure mechanisms.

In the present thesis the governing failure mechanisms for laminates based on glass fibre non-crimp fabrics (NCFs) and unsaturated polyester have been studied. NCF composite materials are well established within the marine and wind turbine industries due to their very good mechanical properties and cost-efficient manufacturing, and has more recently also started to become very popular within the aerospace industry.

Specimens with impact damage, holes, artificial delaminations, and dents have been tested in compression and examined by post-mortem analyses. Based on the results obtained it is clear that the governing failure mechanism for the specimens with impact damage and artificial delaminations was delamination growth, while the governing failure mechanisms for the specimens with holes were fibre microbuckling and kink band formation. A single dent in the specimens did not seem to influence the compressive strength to any great extent, but when the dent was combined with artificial delaminations the compressive strength was significantly reduced and the specimens failed due to delamination growth.

As initiation and propagation of delaminations are very much affected by out-of-plane loadings, compression tests were conducted with a low through-the-thickness pressure. A hole was drilled in the middle of the specimens and a bolt and two washers were used to apply a through-the thickness pressure, and as expected, the initiation and propagation of delaminations was postponed and the compressive strength substantially improved.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet , 2007. , 13 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1304
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-37644Local ID: 37065ISBN: 978-91-85715-57-2 (print)OAI: oai:DiVA.org:liu-37644DiVA: diva2:258493
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2013-12-17
List of papers
1. Compressive failure on non-crimp fabric composites containing impact damage, holes and artificial defects
Open this publication in new window or tab >>Compressive failure on non-crimp fabric composites containing impact damage, holes and artificial defects
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The present study concerns compressive failure of glass fibre NCF composite laminates. The objectives of the study are firstly to give insight into the mechanisms leading to failure, and secondly to provide guidelines for development of physically based engineering models.

The governing failure mechanism for laminates with impact damage, artificial delaminations as well as artificial delaminations and holes was delamination growth, while the governing failure mechanism for laminates with holes was fibre microbuckling and kink band formation. A single artificial dent in the specimens did not seem to reduce the compressive strength to any great extent, but when the dent was combined with artificial delaminations the compressive strength was substantially reduced and the specimens failed due to delamination growth.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-102644 (URN)
Available from: 2013-12-17 Created: 2013-12-17 Last updated: 2013-12-17
2. Effects on through-the-thickness pressure on the compressive failure of non-crimp fabric composites
Open this publication in new window or tab >>Effects on through-the-thickness pressure on the compressive failure of non-crimp fabric composites
(English)Manuscript (preprint) (Other academic)
Abstract [en]

This paper presents results from an experimental investigation of the influence of a low through-the- thickness pressure on the compressive failure of glass fibre non-crimp fabric composite laminates. Specimens with holes and artificial delaminattons have been manufactured and tested both with and without through-the-thickness pressure, and based on the results obtained it is clear that fibre microbuckling and kinking governs final failure of laminates with open holes, while initiation and propagation of delaminations governs final failure of laminates with artificial delaminations. However, by applying a low through-the-thickness pressure, initiation and propagation of delaminations can be prevented, or at least postponed, and the compressive failure strength thereby substantially improved.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-102645 (URN)
Available from: 2013-12-17 Created: 2013-12-17 Last updated: 2013-12-17

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Isaksson, Claes

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