Piezoresistive response of carbon nanotube and carbon fiber/epoxy composites under cyclic loading

Maintaining the mechanical properties and long-term operational safety is considered the main challenge for composite materials under cyclic loading. This work presents mechanical performance of tri-component composites based on multiwall carbon nanotubes (MWCNTs), carbon fibres (CFs) and epoxy resin, and their electrical conductance property for applications like strain gauges. As a result of incorporation of MWCNTs into the epoxy resin in the composite's morphology, their electrical, mechanical and piezoresistive performance can indicate the self-sensing of carbon fiber reinforced epoxy resin matrix (CF/Epoxy matrix) composites; and thus its influence has been systematically examined. The inclusion of multiwall carbon nanotubes increased the resin bonding to the surface of the CF's leading to an increased electrical conductivity and mechanical performances. The piezoresistive performance was significantly influenced by the amount of MWCNTs added to the resin, where the Gauge Factor (GF) with respect to the MWCNTs concentration under cyclic tensile and cyclic bending were in the range of 0.6 similar to 1.5 and 2.5 similar to 5.5 respectively. Moreover, the piezoresistive behaviour of the composite samples showed reasonable sensitivity, stability, and reversibility under cyclic mechanical loading, and the samples withstood more than 500 cycles of load without detectable loss in performance. The exceptional mechanical, electrical and piezoresistive performance and easy manufacturing process of the tri-component composites make them attractive for applications such as self-monitoring structural components.