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Dual Scale Porosity and Interlaminar Properties of Composite Materials
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In the strive towards reduced fuel consumption and lower emissions, low structural weight is becoming a key factor in the design of advanced vehicle and aerospace structures. Whereas most traditional construction materials are seemingly reaching their limitations, composite materials with their high specific properties offer possibilities to further reduce weight. In high demand structural applications, the quality of the composite material is of utmost importance, requiring the material to be void free and the matrix well distributed as a binder for the load carrying reinforcement. To achieve proper wetting of the fibres, knowledge of the flow resistance of the porous fibre reinforcement is required. It is normally expressed in terms of permeability.

Fibre reinforcements in composite materials are normally regarded as a heterogeneous porous media since both fabric and tows are porous but at different length scales. In order to numerically compute the permeability of such media, one of following two approaches can be used. Either filaments are added one-by-one into the modelled geometry (resolved model) or the tows are considered as porous homogenised media. In the latter case expression for the intra-tow permeability is needed.

In this thesis, a porous homogenised tow model is benchmarked with a resolved model to the level of refinement possible without being too expensive computationally. Based on this approach, the permeability of complex three- dimensional (3D) textiles is computed utilizing computational fluid dynamics (CFD) analysis. The effect of inter- and intra-tow porosity on the overall permeability of 2D and 3D structures is analysed and discussed in relation to contradictions found in past studies. A clearer picture of the problem is presented, which will be helpful in future modelling and understanding of the permeability of complex structures. In an experimental study, the overall fibre volume fraction as well as the tow compaction are varied and their influence on the permeability is measured. Experimental studies show good agreement with numerical simulations.

The interlaminar shear strength of thermoplastic composite materials is studied and the influence of specimen size is examined. Using finite element (FE) analysis it is shown that size effects may be partly due to statistical effects and partly due to the higher number of composite layers in thicker specimens.

The effect of processing on the interlaminar delamination toughness of car-bon/polyamide 12 (C/PA12) is studied. It is observed that processing conditions have vital effect on the interlaminar delamination of thermoplastic composites. The mode I crack energy release rate (GIc) of C/PA12 is found to be 15 times higher than for conventional thermoset based composites and 1.5 times higher than for a thermoset composite with stitched reinforcement through the thickness. The best performing C/PA12 composite is manufactured in a hydraulic press equipped with a cold tool, thereby showing potential for both cost and time efficient manufacturing.

 

 

 

 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. , xiii, 39 p.
Series
TRITA-AVE, ISSN 1651-7660 ; 2014:15
National Category
Aerospace Engineering
Identifiers
URN: urn:nbn:se:kth:diva-145718ISBN: 798-91-7595-185-0 OAI: oai:DiVA.org:kth-145718DiVA: diva2:720484
Public defence
2014-06-17, Kollegiesalen, Brinellvägen 8, KTH, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

QC 20150602

Available from: 2014-06-04 Created: 2014-05-27 Last updated: 2015-06-23Bibliographically approved
List of papers
1. Effect of dual scale porosity on the overall permeability of fibrous structures
Open this publication in new window or tab >>Effect of dual scale porosity on the overall permeability of fibrous structures
2014 (English)In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 103, 56-62 p.Article in journal (Refereed) Published
Abstract [en]

The effect of various parameters on the overall permeability of a two dimensional dual scale fibrous structure is studied employing computational fluid dynamics. The permeability of the structure is computed using two models; one resolved and one with homogenised porosity. The homogenised porous tow model is compared with the resolved model to the level of resolution the resolved model can provide at reasonable computational cost. Good agreement is found between the two numerical models. The porous homogenised tow model is then used to study the effect of inter-tow and intra-tow porosity on the overall permeability. It is shown that the effect of intra-tow porosity on the overall permeability is insignificant, while the inter-tow porosity on the other hand has a very strong influence on the overall permeability. Good correlation is also shown with results from previous experimental and numerical studies. For relatively low tow to filament radius ratios (R-t/R-f) there can be some influence from the intra-tow porosity on the overall permeability. However, it is negligible for higher ratios (R-t/R-f > 10(2)), i.e. in the regime where most fibre reinforcements for composite materials are found.

Place, publisher, year, edition, pages
Elsevier, 2014
Keyword
Carbon fibres, Porosity/voids, Transport properties, Multiscale modelling, Resin transfer moulding (RTM)
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-155779 (URN)10.1016/j.compscitech.2014.08.008 (DOI)000343364100009 ()2-s2.0-84906837658 (Scopus ID)
Funder
XPRES - Initiative for excellence in production research
Note

QC 20150623. QC 20160129

Available from: 2014-11-13 Created: 2014-11-13 Last updated: 2017-12-05Bibliographically approved
2. An experimental study of the influence from fibre architecture on the permeability of 3D-woven textiles
Open this publication in new window or tab >>An experimental study of the influence from fibre architecture on the permeability of 3D-woven textiles
2015 (English)In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 34, no 17, 1444-1453 p.Article in journal (Refereed) Published
Abstract [en]

In this work experimental measurements of the permeability of fully interlaced 3D-woven carbon fibre preforms are performed using the unsaturated parallel flow method. The effect on the permeability from three different parameters is studied by altering the architecture of woven preforms and varying mould sizes in a duct flow set-up. Influences from the geometrically different surface layers of the woven preforms, from fibre volume fraction and from warp yarn crimp are studied. The measurements show negligible influence on the permeability from crimp and the fraction of weave surface layers while the fibre volume fraction has a prominent influence. However, the effect is not consistent in terms of fibre volume fraction variation alone but depends on how it is varied.

Place, publisher, year, edition, pages
Sage Publications, 2015
Keyword
Fabrics, textiles, 3-dimensional reinforcement, resin flow
National Category
Vehicle Engineering Composite Science and Engineering
Research subject
Vehicle and Maritime Engineering
Identifiers
urn:nbn:se:kth:diva-145994 (URN)10.1177/0731684415593351 (DOI)000360099600008 ()2-s2.0-84939602292 (Scopus ID)
Funder
XPRES - Initiative for excellence in production researchEU, FP7, Seventh Framework Programme, 266026
Note

QC 20160222

Available from: 2014-06-04 Created: 2014-06-04 Last updated: 2017-12-05Bibliographically approved
3. A numerical study of the influence from architecture on the permeability of 3D-woven fibre reinforcement
Open this publication in new window or tab >>A numerical study of the influence from architecture on the permeability of 3D-woven fibre reinforcement
2015 (English)In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 74, 18-25 p.Article in journal (Refereed) Published
Abstract [en]

Various modelling aspects of the permeability of three-dimensional (3D) woven textile preforms are studied using computational fluid dynamics (CFD). The models are built using a recently developed technique able to generate close to authentic representations of 3D textile arrangements. One objective of the study is to investigate how parameters such as the tow architecture and the level of detail in the CFD models influence the results. A second objective is to investigate how the inter and intra-tow porosity affect the permeability. They are varied in a way that somewhat resembles how they would change during compaction, although compaction as such is not modelled. It is concluded that the intra-tow porosity has little effect on the overall permeability of a 3D-woven preform. Detailed modelling of local variation of the intra-tow porosity is thus redundant, which is also demonstrated. The inter-tow porosity, on the other hand, has a prominent influence on the overall permeability. The overall permeability is inherently anisotropic but when the inter-tow porosity is increased the permeability does not increase uniformly but becomes more isotropic. Good agreement is obtained between the numerical simulations and experiments performed in a parallel study.

Place, publisher, year, edition, pages
Elsevier, 2015
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-145996 (URN)10.1016/j.compositesa.2015.02.019 (DOI)000356553600003 ()2-s2.0-84926615195 (Scopus ID)
Funder
XPRES - Initiative for excellence in production research
Note

Updated from manuscript to article in journal. QC 20150602

Available from: 2014-06-04 Created: 2014-06-04 Last updated: 2017-12-05Bibliographically approved
4. Specimen size effects on the interlaminar shear strength of thermoplastic composites
Open this publication in new window or tab >>Specimen size effects on the interlaminar shear strength of thermoplastic composites
(English)Manuscript (preprint) (Other academic)
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-145997 (URN)
Note

QS 2014

Available from: 2014-06-04 Created: 2014-06-04 Last updated: 2014-06-04Bibliographically approved
5. Interlaminar fracture toughness of carbon/polyamide 12 composites
Open this publication in new window or tab >>Interlaminar fracture toughness of carbon/polyamide 12 composites
(English)Manuscript (preprint) (Other academic)
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-145998 (URN)
Note

QS 2014

Available from: 2014-06-04 Created: 2014-06-04 Last updated: 2014-06-04Bibliographically approved

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