Multiscale Analysis of Multifunctional Composites

Abstract: Conventional polymer composites are highly demanding due to their high strength and stiffness, low weight, easy processing and corrosion resistance. However, their weak out of plane properties restricts their use in high performance applications, such as aerospace, military and automotive components. The exceptional mechanical, electrical and thermal properties of carbon nanotubes offer great potential to improve out of plane properties of the fibre reinforced composites and imparts multifunctionality. This thesis work focuses on investigating different properties of multiscale composite such as, electrical conductivity and mechanical properties under cyclic loading conditions. One important aim of this project work is to study  relationship between the nanotube concentration and the resulting properties of the multiscale composites. The multiscale composites characterized in this thesis work are manufactured by two different ways, (1) by depositing MWCNTs on carbon fibre via Electrophoretic deposition (EPD) process and then the final manufacturing by resin transfer moulding and (2) by mixing MWCNTs in resin and manufacturing multiscale composite by hand lay-up.  The electrical conductivity of multiscale composites was tested at different lengths, currents, nanotube content and alignment voltages. The electrical conductivity measurements performed at different sample lengths showed that the conductivity strongly depends on length along which it is measured. All samples showed lower conductivity values at longer lengths and higher at smaller lengths. The matrix doped multiscale composites did not show any enhancement in conductivity due to improperly dispersed nanotubes whereas in fibre doped multiscale composites, the enhancement in conductivity was insignificant compared to the reference sample. However, a percolation threshold is observed at 0.005% MWCNTs content. This sample showed highest conductivity among multiscale composites. The results from mechanical characterization showed that thin 90°ply composite perform better under cyclic loading conditions by delaying matrix microcracking. Among the multiscale composites, the sample with 0.005% nanotubes showed enhanced interfacial shear strength by delaying microcracking.