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Effect of dual scale porosity on the overall permeability of fibrous structures
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.ORCID iD: 0000-0002-9207-3404
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.ORCID iD: 0000-0002-6616-2964
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. Vol. 103, 56-62 p.
Keyword [en]
Carbon fibres, Porosity/voids, Transport properties, Multiscale modelling, Resin transfer moulding (RTM)
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-155779DOI: 10.1016/j.compscitech.2014.08.008ISI: 000343364100009Scopus ID: 2-s2.0-84906837658OAI: oai:DiVA.org:kth-155779DiVA: diva2:763102
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
In thesis
1. Dual Scale Porosity and Interlaminar Properties of Composite Materials
Open this publication in new window or tab >>Dual Scale Porosity and Interlaminar Properties of Composite Materials
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:nbn:se:kth:diva-145718 (URN)798-91-7595-185-0 (ISBN)
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

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Hallström, StefanÅkermo, Malin

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