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Approximate Analytical Constitutive Model for Non-Crimp Fabric Composites
2005 (English)In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 36, no 2, 173-181 p.Article in journal (Refereed) Published
Abstract [en]

In this paper, a study set on development and validation of constitutive models to account for out-of-plane fibre waviness in Non-crimp fabric (NCF) composites is presented. For this purpose, a mathematical model based on Timoshenko beam theory applied on curved beams, representing wavy tows in a NCF composite layer is employed. Stiffness knock-down factors operating at the ply level are established and introduced in laminate theory. The developed models are validated on laminates by comparison between predictions and experimental data as well as by comparison with numerical results for a cross-ply laminate. Application of the models on NCF composite laminates (cross-ply and quasi-isotropic) reveals that the models successfully predict laminate elastic properties.

Place, publisher, year, edition, pages
2005. Vol. 36, no 2, 173-181 p.
Keyword [en]
fabrics/textiles, lamina/ply, elasticity, analytical modelling
National Category
Reliability and Maintenance
Identifiers
URN: urn:nbn:se:kth:diva-5614DOI: 10.1016/j.compositesa.2004.06.007ISI: 000226329500008OAI: oai:DiVA.org:kth-5614DiVA: diva2:10041
Note
QC 20110118Available from: 2006-04-27 Created: 2006-04-27 Last updated: 2017-12-14Bibliographically 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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