PhD Thesis Defence Presentations - Koutroumanis Nikolaos

In recent decades carbon fibres have been increasingly used as a means of reinforcing composites in advanced technological applications due to their excellent mechanical properties. The main parameter that determines the mechanical behavior of a composite material is the quality of the interfacial bond between the host medium and the reinforcement. Many methods have been developed for the surface treatment of carbon fibres, mainly aiming at their surface modification through chemical oxidation, by using electrolytic methods, plasma treatment etc. This improves the interaction between the reinforcement and the matrix by developing appropriate chemical bonds or increasing their surface roughness.

In this work, a mild chemical process (epoxidation) involving functionalization of carbon fibres via an epoxidation reaction at room temperature (RT) is being proposed, followed by mechanical and spectroscopic characterization of modified carbon fibre/epoxy resin composites. A microscale study is carried out by using a single filament model composite, in attempt to apply the shear lag model for assessing the efficiency of the treatment. Large scale fibrous composites have also been prepared for the investigation of macroscopic properties after their chemical treatment. The characterization of the samples is carried out via different techniques such as X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Raman spectroscopy and various mechanical tests.

In addition, hybrid CFRP composite materials are prepared and characterized, by introducing 2D materials (graphene flakes) in order to investigate the effect of the latter on the mechanical properties of the final composite material. Here too, modified composites are studied at the micro level and in real (macroscale) fibrous composites.