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
Impact Loading of Composite and Sandwich Structures
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Low weight is one of the most important factors in the design process of high speed naval ships, road vehicles and aircrafts. Lower structural weight enables the possibility of down-sizing the propulsion system and thus decrease manufacturing and operating costs as well as reducing the environmental impact.

Two efficient ways of reducing the structural weight of a structure is by using high performance composite materials and by using geometrically efficient structures such as the sandwich concept. In addition to good quasi-static performance different structures have dynamic impact requirements. For a road vehicle this might be crash worthiness, an aircraft has to be able to sustain bird strikes or debris impact and a naval ship needs to be protected against blast or ballistic loading. In this thesis important aspects of dynamic loading of composite and sandwich structures are addressed and presented in the appended papers as follows.

In paper A the notch sensitivity of non-crimp fabric glass bre composites is investigated. The notch sensitivity is investigated for several different laminate con gurations at varying tensile loading rate. It is shown that the non-crimp fabrics have very low notch sensitivity, especially for laminate con gurations with a large amount of bres in the load direction. Further, the notch sensitivity is shown to be fairly constant with increasing loading rates (up to 100/s).

In paper B a heuristic approach is made in order to create an analytical model to predict the residual strength of composite laminates with multiple randomly distributed holes. The basis for this model is a comprehensive experimental programme. It is found that unidirectional laminates with holes predominantly fail through three failure modes: global net-section failure, local net-section failure and local shear failure. Each failure mode can be described by a physical geometric constant which is used to create the analytical model. The analytical model can predict the residual strength of unidirectional laminates with multiple, randomly distributed holes with good accuracy.

In paper C and paper D, novel prismatic high performance all-composite sandwich cores are proposed. In paper C an analytical model is developed that predicts the strength and sti ness properties of the suggested cores. In paper D the prismatic cores are manufactured and tested in shear loading and out-of-plane compression loading. Further, the analytical model is used to create failure mechanism maps to map out the overall behaviour of the different core con gurations. The novel cores show very high speci c strength and sti ness and are potential candidates as cores in high performance naval ship hulls.

In paper E the dynamic properties of prismatic composite cores are investigated. The dynamic out-of-plane strength of an unit cell is tested experimentally in a gas gun - Kolsky bar set-up. Especially, different failure mechanisms and their e ect on the structural strength are investigated. It is found that cores with low relative density (slender core members) show very large inertial stabilisation e ects and have a dynamic strength that can be more than seven times higher than the quasi-static strength. Cores with higher relative density show less increase in dynamic strength. The main reason for the dynamic strengthening is due to the strain rate sensitivity of the parent material rather than inertial stabilisation of the core members.

Place, publisher, year, edition, pages
Stockholm: KTH , 2010. , xi, 35 p.
Series
Trita-AVE, ISSN 1651-7660 ; 2010:58
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-25141ISBN: 978-91-7415-746-8 (print)OAI: oai:DiVA.org:kth-25141DiVA: diva2:356090
Public defence
2010-11-08, Sal F3, Lindstedtsvägen 26, KTH, Stockholm, 10:15 (English)
Opponent
Supervisors
Note
QC 20101014Available from: 2010-10-14 Created: 2010-10-11 Last updated: 2012-03-23Bibliographically approved
List of papers
1. Tensile strength of UD-composite laminates with multiple holes
Open this publication in new window or tab >>Tensile strength of UD-composite laminates with multiple holes
2010 (English)In: Composites Science And Technology, ISSN 0266-3538, Vol. 70, no 8, 1280-1287 p.Article in journal (Refereed) Published
Abstract [en]

The residual strength of glass fibre reinforced vinyl-ester laminates with multiple holes was investigated through an experimental programme. Different types of structured hole patterns and hole densities were investigated and analysed using digital image correlation strain measuring technique. Three different failure modes could be observed when the hole patterns and the hole densities were a altered. These three failure modes were used as the foundation for a simple yet effective analytical model in order to predict the residual strength of damaged composite specimens. Finally, a number of laminates with randomly distributed holes were tested experimentally. The analytical model can predict the failure mode and failure strength of the experiments with sufficiently good fidelity.

Keyword
Glass fibres, Strength, Notch, Multiple holes
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-25107 (URN)10.1016/j.compscitech.2010.04.005 (DOI)000279040300011 ()2-s2.0-77953127295 (Scopus ID)
Note

QC 20101011

Available from: 2010-10-11 Created: 2010-10-08 Last updated: 2015-05-07Bibliographically approved
2. Blast Loading of All-Composite Prismatic Sandwich Cores
Open this publication in new window or tab >>Blast Loading of All-Composite Prismatic Sandwich Cores
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The compressive response of corrugated carbon bre reinforced epoxysandwich cores has been investigated using a Kolsky-bar set-up. Theloading rates tested within this study are similar to those that areexpected when a sandwich core is compressed due to a blast event.Experiments show signi cant strength enhancement as the loading rateincreases. Although material rate sensitivity accounts for some amountof the strength enhancement, it has been shown that the majority of thestrength enhancement is due to inertial stabilisation of the core members.

Keyword
Corrugated cores, Sandwich structures, Blast protection, Micro inertia
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-25109 (URN)
Note
QC 20101011Available from: 2010-10-11 Created: 2010-10-08 Last updated: 2010-10-14Bibliographically approved
3. Corrugated all-composite sandwich structures. Part 2: Failure mechanisms and experimental programme
Open this publication in new window or tab >>Corrugated all-composite sandwich structures. Part 2: Failure mechanisms and experimental programme
2009 (English)In: Composites Science And Technology, ISSN 0266-3538, Vol. 69, no 7-8, 920-925 p.Article in journal (Refereed) Published
Abstract [en]

A novel corrugated composite core, referred to as a hierarchical corrugation, has been developed and tested experimentally. Hierarchical corrugations exhibit a range of different failure modes depending on the geometrical properties and the material properties of the structures. In order to understand the different failure modes the analytical strength model, developed in part I of this paper, was used to make collapse mechanism maps for the different corrugation configurations. If designed correctly, the hierarchical structures can have more than 7 times higher weight specific strength compared to its monolithic counter part. The difference in strength arises mainly from the increase in buckling resistance of the sandwich core members compared to the monolithic version. The highest difference in strength is seen for core configurations with low overall density. As the density of the core increases, the monolithic core members get stockier and more resistant to buckling and thus the benefits of the hierarchical structure reduces.

Place, publisher, year, edition, pages
Elsevier, 2009
Keyword
Structural composites, Sandwich structures, Hierarchical structures, beams
National Category
Composite Science and Engineering
Identifiers
urn:nbn:se:kth:diva-18452 (URN)10.1016/j.compscitech.2008.11.035 (DOI)000266380700007 ()2-s2.0-64849106855 (Scopus ID)
Note

QC 20100525

Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2015-05-07Bibliographically approved
4. Corrugated all-composite sandwich structures. Part 1: Modeling
Open this publication in new window or tab >>Corrugated all-composite sandwich structures. Part 1: Modeling
2009 (English)In: Composites Science And Technology, ISSN 0266-3538, Vol. 69, no 7-8, 913-919 p.Article in journal (Refereed) Published
Abstract [en]

An analytical model for the compressive and shear response of monolithic and hierarchical corrugated composite cores has been developed. The stiffness model considers the contribution in stiffness from the bending- and the shear deformations of the core members in addition to the stretching deformation. The strength model is based on the normal stress and shear stress distribution over each core member when subjected to a shear or compressive load condition. The strength model also accounts for initial imperfections. In part 1 of this series, the analytical model is described and the results are compared to finite element predictions. In part 2, the analytical model is compared to experimental results and the behaviour of the corrugated structures is investigated more thoroughly using failure mechanism maps.

Place, publisher, year, edition, pages
Elsevier, 2009
Keyword
Structural composites, Sandwich structures, Corrugated cores, lattice truss structures, compressive behavior, core, beams, performance, aluminum, collapse, plates
National Category
Composite Science and Engineering
Identifiers
urn:nbn:se:kth:diva-18451 (URN)10.1016/j.compscitech.2008.11.030 (DOI)000266380700006 ()2-s2.0-64849104143 (Scopus ID)
Note

QC 20100525

Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2015-05-07Bibliographically approved
5. Notch and Strain Rate Sensitivity of Non-Crimp Fabric Composites
Open this publication in new window or tab >>Notch and Strain Rate Sensitivity of Non-Crimp Fabric Composites
2009 (English)In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 69, no 6, 793-800 p.Article in journal (Refereed) Published
Abstract [en]

The notch and strain rate sensitivity of noncrimp glass fibre/vinyl-ester laminates subjected to uniaxial tensile loads has been investigated experimentally. Two set of notch configurations were tested; one where circular holes were drilled and another where fragment simulating projectiles were fired through the plate creating a notch. Experiments were conducted for strain rates rangingfrom 10-4/s to 102/s using servo hydraulic machines. A significant increase in strength with increasing strain rate was observed for both notched and unnotched specimens. High speed photography revealed changes in failure mode, for certain laminate configurations, as the strain rate increased. The tested laminate configurations showed fairly small notch sensitivity for the whole range of strain rates.

Place, publisher, year, edition, pages
Elsevier, 2009
Keyword
strain rate, non-crimp, notch sensitivity, glass fibre, vinyl-ester, dynamic, impact
National Category
Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-65571 (URN)10.1016/j.compscitech.2008.06.002 (DOI)000265518200013 ()2-s2.0-62849109955 (Scopus ID)
Conference
16th International Conference on Composite Materials
Note

QC 20120203

Available from: 2012-02-03 Created: 2012-01-25 Last updated: 2017-12-08Bibliographically approved

Open Access in DiVA

fulltext(1542 kB)7439 downloads
File information
File name FULLTEXT01.pdfFile size 1542 kBChecksum SHA-512
210e7e7ddfa73456e0edbbec19474bf3718f27e6e35c683fa3b7690e6c2946a81e17818236d9ee95d5c6ece3d3f5baebc0391df7453f814ab96d812e5eb5ba44
Type fulltextMimetype application/pdf

Search in DiVA

By author/editor
Kazemahvazi, Sohrab
By organisation
Lightweight Structures
Fluid Mechanics and Acoustics

Search outside of DiVA

GoogleGoogle Scholar
Total: 7440 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: 954 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