Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Physically Based Engineering Models for NCF Composites
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
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: urn:nbn:se:kth:diva-3927ISBN: 91-7178-316-4 (print)OAI: oai:DiVA.org:kth-3927DiVA: diva2:10046
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
List of papers
1. Approximate Analytical Constitutive Model for Non-Crimp Fabric Composites
Open this publication in new window or tab >>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.

Keyword
fabrics/textiles, lamina/ply, elasticity, analytical modelling
National Category
Reliability and Maintenance
Identifiers
urn:nbn:se:kth:diva-5614 (URN)10.1016/j.compositesa.2004.06.007 (DOI)000226329500008 ()
Note
QC 20110118Available from: 2006-04-27 Created: 2006-04-27 Last updated: 2017-12-14Bibliographically approved
2. Failure of NCF Composites Subjected to Combined Compression and Shear Loading
Open this publication in new window or tab >>Failure of NCF Composites Subjected to Combined Compression and Shear Loading
2006 (English)In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 66, no 15, 2865-2877 p.Article in journal (Refereed) Published
Abstract [en]

Earlier studies have shown that formation of kink bands is the mechanism that is likely to govern failure of compression loaded non-crimp fabric (NCF) composite laminates. Because of this, a failure criterion for prediction of failure caused by kinking under multiaxial (axial compression and shear) loading has been adapted to a NCF composite system. The criterion has been validated for compression tests of quasi-isotropic laminates tested in uniaxial compression. By performing compression tests of the laminate at different off-axis angles, it was possible to vary the ratio of compressive axial stress/shear stress in the specimens. The test results proved that the criterion works well for predictions of kinking governed failure for the present material system. Detailed fractographic studies confirmed that formation of kink bands was the mechanism responsible for specimen failure. Kink bands were also found to develop at loads significantly lower than load at specimen failure.

Keyword
fabrics/textiles, fracture, failure criterion, fractography
National Category
Reliability and Maintenance
Identifiers
urn:nbn:se:kth:diva-5615 (URN)10.1016/j.compscitech.2006.02.021 (DOI)000241654500028 ()2-s2.0-33748573245 (Scopus ID)
Note
Uppdaterad från accepted till published(20110118). QC 20110118Available from: 2006-04-27 Created: 2006-04-27 Last updated: 2017-12-14Bibliographically approved
3. Compressive failure of impacted NCF composite sandwich panels - Characterisation of the failure process
Open this publication in new window or tab >>Compressive failure of impacted NCF composite sandwich panels - Characterisation of the failure process
2004 (English)In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 38, no 6, 495-514 p.Article in journal (Refereed) Published
Abstract [en]

In the present study, non-crimp fabric (NCF) composite face sheet sandwich panels have been tested in compression after impact (CAI). Damage in the face sheets was characterised by fractography. Compression after impact loaded panels were found to fail by plastic fibre microbuckling (kinking) in the damaged face sheet. Studies of panels for which loading was interrupted prior to failure revealed extensive stable kink band formation at several positions and in numerous plies. Kink bands initiated and propagated within a wide region close to the point of impact. In addition, kink bands initiated in zones with high shear stresses, away from the impact centre line. Consequently, the fractographic results from this investigation do not support the assumption of modelling the impact damage as an equivalent hole. To achieve accurate predictions of kink band initiation, the stress field must be known. The results from this study imply that bending effects caused by remaining dent or material eccentricities in the damaged region must be considered.

Keyword
CAI, CFRP, Damage tolerance, Fractography, Sandwich
National Category
Reliability and Maintenance
Identifiers
urn:nbn:se:kth:diva-5616 (URN)10.1177/0021998304040559 (DOI)000220671000003 ()2-s2.0-1842526619 (Scopus ID)
Note

QC 20110119

Available from: 2006-04-27 Created: 2006-04-27 Last updated: 2017-12-14Bibliographically approved
4. Compressive failure of NCF composites
Open this publication in new window or tab >>Compressive failure of NCF composites
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
Series
Proceedings of the American Societyfor Composites Twentieth Technical Conference, Vol. 3
National Category
Reliability and Maintenance
Identifiers
urn:nbn:se:kth:diva-5617 (URN)2-s2.0-84871010206 (Scopus ID)978-162276282-8 (ISBN)
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
5. Compression After Impact Strength of NCF Composite Sandwich Panels
Open this publication in new window or tab >>Compression After Impact Strength of NCF Composite Sandwich Panels
(English)Article in journal (Other academic) Submitted
National Category
Reliability and Maintenance
Identifiers
urn:nbn:se:kth:diva-5618 (URN)
Note
QS 20120326Available from: 2006-04-27 Created: 2006-04-27 Last updated: 2012-03-26Bibliographically approved

Open Access in DiVA

fulltext(2028 kB)3138 downloads
File information
File name FULLTEXT01.pdfFile size 2028 kBChecksum MD5
7272221a5033e2273f79f11e9cf9d8e559ad9ab3523bf094e9ba07158d5b34f86e12c7f6
Type fulltextMimetype application/pdf

Search in DiVA

By author/editor
Edgren, Fredrik
By organisation
Aeronautical and Vehicle Engineering
Reliability and Maintenance

Search outside of DiVA

GoogleGoogle Scholar
Total: 3141 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 1076 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf