6 replies to this topic

[muppet]

An easy question for you boffins, with a one-word answer: Does CF conduct electricity?

I believe it does conduct electicity, because I know that pure carbon conducts electricity quite well. But just how well? Does CF's resistance compare with metals (like steel or aluminium) so that a carbon-fibre tub can be used as part of an electric circuit? On the junky old home-made bitza chassis I worked on 20 years ago, the alloy chassis was used as an earth-return. Is the same thing done these days with CF tubs?

[Jezztor]

I'm not 100% percent about this, but pure CF in tow form does conduct electricity, but the resin which cures the CF on CF race cars prevents it from conducting. Not sure, i've been wanting 2 ask this q for a while

Jezz

[desmo]

Yes. Interestingly the material's conductivity is potentially useful as a fault detection parameter:

Carbon fibers used in advanced composite structures are piezoresistive. These fibers are inherently sensors because of its property. Therefore, Carbon Fiber Reinforced Polymer (CFRP) composites can be considered to be self monitoring materials without any need for additional sensing elements. However for this to become reality the conductivity map of the entire structure need to be constructed and relationship between the conductivity and various usage and damage related variables need to be established. It is known that internal damage, such as fiber fracture and delamination, decreases the conductivity of the composite laminates. The complexity in characterizing CFRP conductivity arises because it is anisotropic and influenced by humidity, temperature, strain, and non-aligned fibers. In calculating the resistivity of a laminate, interface resistivity is to be taken into account too. The experimental and numerical research is being conducted to model the resistivity of a single unidirectional layer.

Here is a list of some related published literature:

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Ceysson, Olivier; Risson, Tania; Salvia, Michelle; 1996. Carbon fibres: sensor components for smart materials Proceedings of SPIE - The International Society for Optical Engineering 3rd Int. Conference on Intelligent Materials and 3rd European Conference on Smart Structures and Materials Jun 3 1996 v 2779 1996 Lyon, Fr, p 136-141
Chekanov, Yuri; Ohnogi, Ryuji; Asai, Shigeo; Sumita, Masao 1999. Electrical properties of epoxy resin filled with carbon fibers. Journal of Materials Science 34 22 p 5589-5592
Chen P.W., Chung D.D.L. 1993. Carbon reinforced concrete as a smart material capable of non-destructive flaw detection. Smart Mater. Structures 2: 22-30
Chen P.W., Chung D.D.L. 1996. Concrete as a new strai/stress sensor. Composites Part B 27B: 11-23
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Chung, D.D.L. 1995. Strain sensors based on the electrical resistance change accompanying the reversible pull-out of conducting short fibers in a less conducting matrix. Smart Materials and Structures v4 n1 p 59-61
Chung D.D.L., Wang S. 1999. Carbon fiber polymer matrix composite as a semiconductor and concepts of optoelectronic and electronic devices made from it. Smart Mater, Struct. 8: 161-166
Crasto, A.S.; Kim, R.Y.; 1994. Using carbon fiber piezoresistivity to measure residual stresses in composites. Proceedings of the 8th Technical Conference of the American Society for Composites (ASC) Oct 19-21 1993 1994 p 162-173
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Davies W.F.A. 1974. The dielectric constant of fibre composites. J. Physics D: App. Phys. 7: 120-130. (micromechanics-type paper)
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Kaddour, A. S., Al-Salehi, F. A. R., Al-Hassani, S. T. S., and Hinton, M. J., "Electrical Resistance Measurement Technique for Detecting Failures in CFRP Materials at High Strain Rates," Composites Science and Technology, Vol. 51, No. 3, 1994, pp. 377–385.
Kang, Ho-Jong; Buchman, E.; Isayev, A.I.; 1991. Measurement of processing variables in manufacturing of thermoplastic composites. SAMPE Journal v 27 n 5 p 21-27 (measurement of resistance during cure. Did not show much promise)
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Lian, Anqing; Dao, Le H.; Zhang, Ze; King, Martin W.; Guidoin, Robert G. 2000. Electrical properties of conductive polypyrrole-coated textiles Polymers and Polymer Composites 8 1 2000 p 1-9
Mei, Zhen; Chung, D.D.L. 2000. Effects of temperature and stress on the interface between concrete and its carbon fiber epoxy-matrix composite retrofit, studied by electrical resistance measurement. Cement and Concrete Research 30 5 2000 p 799-802
Michali W., Goedel M., 1994. Using carbon fiber rovings as sensors for the loading of GFRP-parts. Proc. 39th Int. SAMPE Symp. pp. 3103-3111 **
Nakamura, Y.; Nishizawa, K.; Motohira, N.; Yanagida, H.; 1994. Strain dependent electrical resistance of carbon-insulator composite. Journal of Materials Science Letters v 13 n 11 p 829-831
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[Darren Galpin]

Pure carbon does not always conduct electricity - it depends on the crystal structure (or allotrope to use the proper terminology). Carbon in the form of graphite, fullerenes (those famous buckyballs) and carbon fibre can conduct, whereas diamond will not. All are carbon based.

[Yelnats]

Good reply Desmo.

There's been many a quite evening that I've settled down with a heady tomb on carbon fibre condutivity, my favourite being.......

Li P., Sttttrieder W., Joy T., 1982. Random lattice conductivity calculations for a graphite/epoxy ply of finite thickness. J. Composite Materials 16: 53-64 ... which was on your list.;)

Interestingly the electrical mapping of carbon fibre structures resemples the testing of bridge decks for degredation by electrical conductivity, something I was involved with in my former carrer in highway design. And the latest structures (bridges) in Canada have used carbon fibre in tension to reinforce post-tensioned concrete beams.

To see things come around the complete circle is most satisfying.

[Timm]

I'm not sure it does. If I remember correctly, aircraft with all-'plastic' wings have a fine steel mesh embedded in the layup to conduct lightening to safety so as the fuel-filled tank won't explode

[desmo]

Yeah, I really had nothing better to do than invent all the stuff in my above post. Busted.

Seriously although steel mesh is used to increase conductivity in the event of a lightning strike in some composite aircraft construction, it is not a case of CF being non-conductive but simply not conductive enough for that eventuality.