Effects of the graphene on the mechanical properties of fibre reinforced polymer - a numerical and experimental study

Mechanical properties of carbon fibre reinforced polymer (CFRP) are greatly affected by interphase between fibre and matrix. Coating fibre with nanofillers, i.e. graphene nanoplatelets (GNPs) or carbon nanotubes (CNTs) has suggested improving the interphase properties. Although the interphase is of small thickness, it plays an important role. Quantitative characterisation of the interphase region using an experimental technique such as nanoindentation, dynamic mechanical mapping remains challenging. More recently, computational modelling has become an alternative way to study the effects of interphase on CFRP properties. Simulation work of CFRP reinforced with nanofillers mainly focuses on CNTs grown on the fibre surface called fuzzy fibre reinforced polymers. Modelling work on the effects of GNPs on CFRP properties is rather limited. This project aims to study numerically and experimentally the effects of the nano-reinforced interphase on mechanical properties of CFRP. A multiscale model was developed to study the effects of the GNPs reinforced interphase on the elastic properties of CFRP laminate. The effective material properties of the reinforced interphase were determined by considering transversely isotropic features of GNPs and various orientation. The presence of GNPs in the interphase enhances the elastic properties of CFRP lamina, and the enhancement depends on its volume fraction. The incorporation of randomly orientated GNPs in the interphase increased longitudinal and transverse lamina moduli by 5 and 12 % respectively. While aligned GNPs in the interphase yielded less improvement. The present multiscale modelling was able to reproduce experimental measurements for GNPs reinforced CFRP laminates well. The multiscale model was also proven successful in predicting fuzzy fibre reinforced polymer. Moreover, the interphase properties were inversely quantified by combining with the multiscale model with some standard material testing. A two-step optimisation process was proposed, which involved the microscale and macroscale modelling. Based on the experimental data on flexural modulus, the lamina properties were derived at macroscale modelling, which were later used to determine the interphase properties from the optimisation at the microscale. The GNPs reinforced interphase modulus was 129.1 GPa which is significantly higher than epoxy coated carbon fibre of 60.51 GPa. In the experiment, a simple spraying technique was proposed to introduce GNPs and CNTs into the CFRP. Carbon fibre prepreg was sprayed with a nanofillers-ethanol solution using an airbrush. The extremely low volume fraction of nanofillers introduced between prepreg plies caused a noticeable improvement in mechanical properties, i.e. 7% increase in strain energy release. For the first time, the GNPs-ethanol-epoxy solution was sprayed directly on the carbon fibre fabric. Resultant nano-reinforced interphase created on fibre surface showed moderate improvement in samples flexural properties. In conclusion, a multiscale modelling framework was developed and tested. The GNPs reinforced interphase improved the mechanical properties of CFRP. This enhancement depended on the orientation and volume fraction of GNPs in the interphase. Spraying was a cost-effective method to introduce nanofillers in CFRP and showed huge potential for the scale-up manufacturing process. In a combination of multiscale framework and optimisation process, the nanofillers reinforced interphase was for the first time determined. This framework could be used to optimise the development process of new fibre-reinforced composites.