Hierarchical carbon-fibre reinforced polymer (CFRP) composites utilising directly grown graphene nanoflakes

  • Anastasios Karakasidis

Student thesis: Doctoral Thesis


The development of nanoscale reinforcements, which can tailor mechanical performance and impart multiple functionalities on carbon fibre reinforced polymer (CFRP) composites, remains a challenge for their largescale adoption in diverse applications ranging from aerospace to transportation and construction industries. During the past years, many nanoscale reinforcements were used for the enhancement of CFRP, with carbon nanotubes (CNTs) being the one that utilized mostly. A relatively new and unexplored so far nano-reinforced hierarchical structure with extreme potential for all around properties’ reinforcement, is the graphene nanoflakes (GNFs) coated carbon fibre (CF).

Within the scope of this thesis, GNFs were directly grown onto CFs, using two
catalyst-free and straight forward techniques: i) microwave plasma enhanced chemical vapour deposition (mw-PECVD) and ii) radio frequency plasma enhanced chemical vapour deposition (rf-PECVD). Moreover, in order to compare the grown hierarchical structures with ones originating from other alternative methods, a novel and one-step CO2 laser texturing process of CFs was examined as well.

A remarkable 28% enhancement in the tensile strength of the hybrid fibres (mw-PECVD growth) was observed via single-fibre tensile strength tests, whereas the interfacial shear strength (IFSS) increased by 101.5%. The results of this thesis demonstrate that GNFs not only improve the interfacial strength between the GNFs and the epoxy resin but also enhance the in-plane mechanical strength of the CFs—a well-known problem encountered with the direct growth of carbon nanotubes on CFs. In addition, GNFs provided embedded functionality via increased electrical conductivity (60.5% improvement for yarns and 16% for single fibre).

Mode-I, Mode-II interlaminar fracture toughness and tensile strength tests revealed the all-around enhanced mechanical performance (up to 63.9%, 43.8% and 9.67% respectively) of the fabricated hierarchical composites (rf-PECVD GNFs growth), while remarkable enhancement of the out of plane through volume electrical
conductivity by 527% was observed. Generally, the results of this work showed huge potential for multifunctional laminated materials, indicating that the rf-PECVD method is suitable for all around properties’ reinforcement.

Moreover, the results of the CO2 irradiation of the CF fabrics, showed that this method can be considered as a quick and low-cost technique for producing composites with boosted out of plane electrical conductivity (increment up to 18.4%), without negatively affecting the interlaminar region of them (preservation of the Mode-I interlaminar fracture toughness).
Date of Award2022
Original languageEnglish
SponsorsDepartment of Education for Northern Ireland
SupervisorPagona Papakonstantinou (Supervisor) & Alistair McIlhagger (Supervisor)


  • Graphene nanoflakes
  • Hierarchical composites
  • Multifunctional composites
  • CFRP
  • Interlaminar fracture toughness
  • Tensile strength
  • Electrical conductivity

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