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Compressive failure of NCF composites
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. SICOMP AB.
2005 (English)In: Proceedings of the American Societyfor Composites Twentieth Technical Conference, 2005, DEStech Publications, Inc , 2005, 1629-1644 p.Conference paper, Published paper (Refereed)
Abstract [en]

This study concerns compression failure of impacted Non-Crimp Fabric (NCF) composite laminates. Panels with a barely visible impact damage (BVID) have been studied under compression after impact (CAI) conditions. Monolithic laminates have been tested in CAI and the failure mechanisms are identified and discussed. The study on monolithic laminates constitutes a complement to a previous study on NCF laminate face sheets of sandwich panels in a naval application. The results from the present study confirm the findings from the study on sandwich skins; the mechanism controlling failure of CAI loaded NCF laminates is formation of kink bands. It is also found that kink bands develop at loads substantially lower than the load at panel failure. The results also indicate that the typical NCF heterogeneous structure, with fibre bundles separated with resin rich regions and fibre waviness, prevent kink bands from growing unstable immediately after initiation.

Place, publisher, year, edition, pages
DEStech Publications, Inc , 2005. 1629-1644 p.
Series
Proceedings of the American Societyfor Composites Twentieth Technical Conference, Vol. 3
National Category
Reliability and Maintenance
Identifiers
URN: urn:nbn:se:kth:diva-5617Scopus ID: 2-s2.0-84871010206ISBN: 978-162276282-8 (print)OAI: oai:DiVA.org:kth-5617DiVA: diva2:10044
Conference
20th Technical Conference of the American Society for Composites 2005; Philadelphia, PA, United States, 7-9 September, 2005
Note

QC 20110121

Available from: 2006-04-27 Created: 2006-04-27 Last updated: 2014-08-11Bibliographically approved
In thesis
1. Physically Based Engineering Models for NCF Composites
Open this publication in new window or tab >>Physically Based Engineering Models for NCF Composites
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Non-Crimp Fabrics - NCF – are increasingly being used as reinforcements in high performance composite materials. NCF offer the manufacturing advantages from textile preforms in combination with excellent mechanical performance. This study concerns the mechanical performance of NCF composites. Through a combination of experimental work and theoretical studies the mechanisms controlling the mechanical behaviour are explained. Fractography is used as a tool to identify governing mechanisms and link these to the material internal structure. Based on the experimental findings, engineering models are suggested predicting the mechanical behaviour of NCF composite laminates.

A simplified constitutive model is presented that accounts for the fibre tow out-of-plane waviness. The model is based on Timoshenko beam theory applied on curved beams representing wavy tows in a NCF composite lamina. The model calculates stiffness knock-down factors to be applied on lamina homogenised properties.

Experiments show compressive failure of NCF composites to be governed by formation and growth of kink bands. For this reason, a failure criterion predicting kinking failure under multiaxial loading is proposed and validated for a NCF composite system. The criterion is to be used on lamina level in a multiaxial NCF laminate. A test method is proposed for extraction of strength parameters valid for the lamina material in a multiaxial laminate.

Compression-after-impact (CAI) behaviour of NCF composite laminates, as monolithic skins and sandwich panel face sheets, is investigated. Fractographic studies show CAI failure to be controlled by formation of kink bands. The experimental studies reveal that kink bands form at relatively low loads and grow gradually during compressive loading. It is suggested that the notch effect from the gradually developing kink bands cause final catastrophic failure in sandwich panel skins. Finite element analyses, simplistically representing the damage with an idealised notch, are shown to predict panel residual strength with reasonable accuracy.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. ix, 27 p.
Series
Trita-AVE, ISSN 1651-7660 ; 2006:17
National Category
Reliability and Maintenance
Identifiers
urn:nbn:se:kth:diva-3927 (URN)91-7178-316-4 (ISBN)
Public defence
2006-05-05, Sal F3, Lindstedtsvägen 26, Stockholm, 13:15
Opponent
Supervisors
Note
QC 20110120Available from: 2006-04-27 Created: 2006-04-27 Last updated: 2011-01-21Bibliographically approved

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