The overarching objective of the proposed research is to study the effects of the three critical microstructural parameters, namely, (i) carbon nanotube-polymer interfacial strength; (ii) carbon nanotube orientation; and (iii) Level of carbon nanotube dispersion, on the manufacturability of carbon nanotube composites. To achieve this objective the machining mechanics will be examined by employing experimental techniques that include both machining inside an atomic force microscope and machining with a new micro-scribing process recently developed at the University of Illinois. The carbon nanotube polymer composite model developed earlier by the principal investigator and his colleagues, which assumed perfect interface bonding, will be enhanced by explicitly modeling the carbon nanotube-polymer interface using two possible approaches; modeling the interface as a third phase in the microstructure, and, using cohesive zone models for the carbon nanotube-polymer interface. Model validation will be accomplished using the micro-scribing processes.
The benefits to society of this project include an enhanced understanding of the effects of carbon nanotube-polymer interfacial strength on the manufacturability of carbon nanotubes and a substantial increase of their potential for use in micro-scale applications that span fields including biomedical, electronics and defense; for example, applications such as microfluidic circuits for drug delivery, more effectively packaged micro-electronics. As a bridge between the nano- and the macro-worlds, the research pursued in this project will facilitate the education and training of a new generation of leaders in the field of micro-manufacturing. Further, the project researchers will strongly encourage participation of members from under-represented groups by proactively participating in several on-campus/off-campus programs, including Women in Engineering Program; Minority Engineering Program; the McNair Scholar program. An effort will be made to integrate new carbon nanotube composite applications and machinability issues developed in the proposed research into both new and existing courses at the University of Illinois.
A microstructure–level finite element (FE) machining model for CNT–PVA composites has been developed to determine the machinability of nano-composites. The CNT–PVA interface is modeled as the third phase along with the CNT phase and the PVA phase. The constitutive material model for PVA polymer accounts for variable temperature and strain rate over the deformation zone during machining process. The temperature– and strain rate-dependent plastic stress was captured by nano- indentation tests and then fitted with the Eyring rate equation to predict the plastic stress of PVA over a wide range of temperatures and strain rates. The cutting force data reveals that the CNT pull- out/protrusion due to interfacial failure, and the subsequent surface damage are captured accurately by the machining model. The trend of damage against the depth of cut and rake angle at both the CNT loadings is found similar to the trend observed for surface topographies and roughness values from the machining experiments. Increase in both the depth of cut and the rake angle better facilitates the material removal process resulting in lower cutting force, minimal surface damage, and improved surface finish. A study on the effect of interfacial properties, including strength and fracture energy during the machining of CNT PVA composites shows that the subsurface damage reduces when their values increase. However, excessive interfacial strength like perfect bonding results in more surface/subsurface damage because CNTs severely bend in the cutting direction, causing more local deformation and higher stress in composites. The study suggests that the microstructure–level FE machining model developed in this study can be used to minimize the surface/subsurface damages, and improving surface finish during the machining of CNT–polymer composites. The model can help improve manufacturing of the new generation of CNT–polymer composites with better control of interfacial properties by selecting a right combination of physical constituents such as CNT and polymer types, CNT functionalization group that controls chemical bonding at the interface and polymer solvent type.
