Fundamental study of the machinability of carbon nanotube reinforced polymer composites.

摘要

The effective manufacturing of micro/meso-scale parts and products using carbon nanotube (CNT) composites requires a knowledge base that will enable the design of these composites to meet both the micro-scale engineering and manufacturing requirements. This research has sought to understand the effect of CNTs on the machining performance of CNT composites and to identify critical microstructural parameters that influence their machinability.;Polycarbonate-based CNT composites containing 1.75%, 5% and 15% by weight of randomly oriented CNTs were studied as part of this work. Extensive testing of the composites was undertaken to characterize the trends in their thermo-mechanical properties as a function of CNT loading. The tensile tests revealed a ductile-to-brittle transition in the composites at a CNT loading of 5% by weight. Since machining is a high strain rate phenomenon, a split Hopkinson pressure bar set-up was also used to study the high strain rate response of these composites.;Micro-milling and orthogonal micro-turning studies revealed that the presence of CNTs in the polymer matrix significantly influences its machinability at the micro-scale. Under the same micro-milling conditions, the CNT composite (15% CNT loading by weight) produced a continuous chip, had lower cutting forces and better surface finish as compared to a conventional carbon fiber composite. The machining studies also showed that at lower loadings of CNTs (1.75% by weight), the visco-elastic/plastic deformation of the polymer phase played a significant role during machining, whereas, at loadings ≥5% by weight, the interface effects and CNT distributions dictated the machining response of the composite. Overall, an increase in CNT loading resulted in a reduction in the minimum chip thickness values, burr dimensions, surface roughness, specific thrust energy, specific cutting energy, and tool wear for the CNT composites.;Alignment of CNTs in the polymer matrix is important from a material property improvement stand point. Therefore, a microstructure-based finite element machining model was used to study the effect of CNT orientation on the machining responses. The predicted machining responses for aligned CNT composites point to the influence of the CNT-polymer interface, CNT orientation (with respect to the cutting direction), and CNT dispersion on the failure mechanisms observed during machining.