The introduction of graphene-related materials (GRMs) in carbon fibre-reinforced polymers (CFRP) has been proved to enhance their mechanical and electrical properties. However, methodologies to produce the 3-phase materials (multiscale composites) at an industrial scale and in an efficient manner are still lacking. In this paper, multiscale CFRP composites containing different GRMs have been manufactured following standard procedures currently used in the aerospace industry with the aim to evaluate its potential application. Graphite nanoplateletelets (GNPs), in situ exfoliated graphene oxide (GO) and reduced graphene oxide (rGO) have been dispersed into an epoxy resin to subsequently impregnate aeronautical grade carbon fibre tape. The resulting prepregs have been used for manufacturing laminates by hand lay-up and autoclave curing at 180°C. A broad characterization campaign has been carried out to understand the behaviour of the different multiscale laminates manufactured. The degree of cure, glass transition temperature and degradation temperature have been evaluated by thermal evolution techniques. Similarly, their mechanical properties (tensile, flexural, in-plane shear, interlaminar shear and mode I interlaminar fracture toughness) have been analysed together with their electrical conductivity. The manufacturing process resulted appropriated for producing three-phase laminates and their quality was as good as in conventional CFRPs. The addition of GO and rGO resulted in an enhancement of the in-plane shear properties and delamination resistance while the addition of GNP improved the electrical conductivity.
Two different types of graphene flakes were produced following solution processing methods and dispersed using shear mixing in a bifunctional (A) and a multifunctional (B) epoxy resin at a concentration of 0.8 and 0.6 wt% respectively. The graphene/epoxy resin mixtures were used to impregnate unidirectional carbon fibre tapes. These prepregs were stacked (seven plies) and cured to produce laminates. The interlaminar fracture toughness (mode-I) of the carbon fiber/graphene epoxy laminates with resin B showed over 56% improvement compared with the laminate without graphene. Single lap joints were prepared using the laminates as adherents and polyurethane adhesives (Sika 7666 and Sika 7888). The addition of graphene improved considerably the adhesion strength from 3.3 to 21 MPa (sample prepared with resin A and Sika 7888) highlighting the potential of graphene as a secondary filler in carbon fibre reinforced polymer composites.
This paper studies the temperature dependence of the electrical resistivity of low-cost commercial graphene-based strips, made from a mixture of epoxy and graphene nanoplatelets. An equivalent homogenous resistivity model is derived from the joint use of experimental data and simulation results obtained by means of a full three-dimensional (3D) numerical electrothermal model. Three different types of macroscopic strips (with surface dimensions of cm2) are analyzed, differing in their percentage of graphene nanoplatelets. The experimental results show a linear trend of resistivity in a wide temperature range (−60°C to +60°C), and a negative temperature coefficient . The derived analytical model of temperature-dependent resistivity follows the simple law commonly adopted for conventional conducting materials, such us copper. The model is then validated by using the graphene strips as heating elements by exploiting the Joule effect. These results suggest that such materials can be used as thermistors in sensing or heating applications.
In the present paper, experimental investigations were conducted to assess the effect of nanomodification on the impact behaviours of hybrid composite plates. Graphene nanoplatelets (GNPs) of two different sizes, 5 and 30 µm, were used to modify a composite material made with 64 wt.% of unidirectional fibres and a low-viscosity epoxy resin. The effect of the nanomodification with 30 µm GNPs was also studied on composite plates prepared with a higher viscosity resin. Three laminate thicknesses (4, 8, and 16 layers) were tested with a standard drop dart testing technique. The peak forces as well as the absorbed energy and the fracture surfaces, observed with a Scanning Electron Microscope (SEM), were compared. Experimental results showed that nano-modification with 5 µm particles had a detrimental effect on both the peak forces and the absorbed energy, whereas the addition of 30 µm GNPs increased the absorbed energy, especially for a laminate thickness of 16 layers. Overall, the experimental results demonstrated that the size of graphene nanoparticles has a significant effect on the impact response of composite laminates.
This paper provides a study of some relevant electro-thermal properties of commercial films made by pressed graphene nano-platelets (GNPs), in view of their use as heating elements in innovative de-icing systems for aerospace applications. The equivalent electrical resistivity and thermal emissivity were studied, by means of models and experimental characterization. Macroscopic strips with a length on the order of tens of centimeters were analyzed, either made by pure GNPs or by composite mixtures of GNPs and a small percentage of polymeric binders. Analytical models are derived and experimentally validated. The thermal response of these graphene films when acting as a heating element is studied and discussed.
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