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Towards electrically conductive and interleaf-toughened carbon black-epoxy-carbon fiber laminates with enhanced lightning strike resistance

Epoxy-carbon fiber prepregs have been used increasingly by civil aerospace industry to manufacture the structural composite parts due to their excellent mechanical, thermo-mechanical and thermal properties at the cured state. Although carbon fibers are electrically conductive, due to the insulating nature of the epoxy matrix, epoxy-carbon fiber prepreg laminates mostly act as a semiconductor in the through-thickness direction. Nowadays, an enhanced through-thickness electrical conductivity is as well desired for modern composite applications, where a certain level of electrostatic dissipation, electromagnetic shielding or an enhanced lightning strike resistance is necessary.

The scientific scope of this work based mainly on the understanding of the effect of the conductive carbon black nanoparticles on the electrical conductivity and the fracture toughness of an aerospace relevant epoxy resin and its unidirectional carbon fiber prepreg laminates. The relationship between the carbon fiber volume content and the through-thickness electrical conductivity of the neat laminates received a particular attention. Furthermore, the influence of a PA6.6 interleaf fleece on the electrical and mechanical properties of the laminates was studied in a detail. Finally, the correlation between the through-thickness electrical conductivity and the lightning strike resistance of PA 6.6 interleaf fleece modified laminates was investigated.

According to the extensive literature survey, although carbon nanotubes and graphene promise a high electrical conductivity as single nanoparticles, carbon black nanoparticles showed as well a great potantial to realize conductive composites at a low nanoparticle content. The addition up to 2 wt.% carbon black in epoxy enhanced the conductivity of the epoxy system already from approximately 7.10-12 S/m to 10-4 S/m.

In the prepreg laminates without the PA6.6 interleaf fleece, the through-thickness electrical conduction was realized mainly by the carbon fiber contacts (≈ 10-1 S/m at 54 vol.% carbon fiber content). An exponential relationship in between the carbon fiber volume content and the throughthickness electrical conductivity of laminates was shown for the first time.

Although the incorporation of the interleaf fleece in laminates almost doubled their fracture toughness, it deteriorated the electrical conductivity in z-direction strongly (from 10-1 S/m to 10-4 S/m). Carbon black nanoparticles however enhanced the electrical conductivity of the interleaf fleece modified laminate tremendeously (from 10-4 S/m to 1 S/m at 2 wt.% additive content) by acting as a conductive bridge in the resin rich interlaminar regions. In addition to the enhanced conductivity, carbon black nanoparticles neither deteriorate the processability of the prepregs nor the thermo - mechanical and mechanical properties of the consolidated prepreg laminates.

Increased through thickness electrical conductivity of laminates reduced the damage after 20 kA strike distinguishably. Consequently, laminates consisting of PA6.6 interleaf fleece together with carbon black nanoparticles (2 wt.%) show an excellent combination of the interlaminar fracture toughness and electrical conductivity. Therefore, carbon black nanoparticle modified epoxy-carbon fiber prepregs open up new composite applications where resistive heating, electro-static dissipation, electro-magnetic shielding or an enhanced lightning strike resistance is desired.

Lesen Sie die deutsche Zusammenfassung auf Kunststoffe.de
Author
 Gökhan Bakis

Gökhan Bakis
Fakultät für Ingenieurwissenschaften
Universität Bayreuth

Information

Free keywords: Prepregs, Fiber Reinforced Polymer Composites, Nanocomposites, Electrical Conductivity, Fracture Toughness, Lightning Strike Resistance, Aerospace
Institute / chair: Fakultät für Ingenieurwissenschaften der Universität Bayreuth
Language: English
Technical consultant for expert services: Professor Dr.-Ing. Volker Altstädt, Professor Dipl.-Ing. Dr.mont. Reinhold W. Lang
Publication year: 2020
Provider: Wissenschaftlicher Arbeitskreis Kunststofftechnik (WAK) / Kunststoffe.de

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