Effect of Carbon Nanotube (CNT) Loading on the Thermomechanical Properties and the Machinability of CNT-Reinforced Polymer Composites

The machinability of carbon nanotube (CNT)-reinforced polymer composites is studied as a function of CNT loading, in light of the trends seen in their material properties. To this end, the thermomechanical properties of the CNT composites with different loadings of CNTs are characterized. Micro-endmilling experiments are also conducted on all the materials under investigation. Chip morphology, burr width, surface roughness, and cutting forces are used as the machinability measures to compare the composites. For composites with lower loadings of CNTs (1.75% by weight), the visco-elastic/plastic deformation of the polymer-phase plays a significant role during machining, whereas, at loadings $≥5%$ by weight, the CNT distribution and interface effects dictate the machining response of the composite. The ductile-to-brittle transition that occurs with an increase in CNT loading results in reduced minimum chip thickness values and burr dimensions in the CNT composite. The increase in thermal conductivity with the increase in CNT loading results in reduced number of adiabatic shear bands being observed on the chips and reduced thermal softening effects at high cutting velocities. Thus, overall, an increase in CNT loading appears to improve the machinability of the composite.