Title

Processing and performance of composites with micro and nanoscale reinforcements

Date of Completion

January 2007

Keywords

Engineering, Mechanical

Degree

Ph.D.

Abstract

Fabrication of composite parts can be done with a variety of methods including pultrusion and filament winding for simple geometries, autoclave curing for high quality parts, and liquid composite molding for complex geometries. While each has its own advantage and application domains, liquid molding is a promising technique for rapid fabrication of net-shaped composite parts. Of the liquid composite molding techniques, vacuum assisted resin transfer molding (VARTM) is renowned for its simplicity and low cost in fabricating large structures. One particular challenge in liquid molding techniques, in general, is the filling of fibrous preform-laden mold with catalyzed resin. The permeability variability causes nonuniformity in the fill patterns, and often leads to entrapped voids and dry spots in the product. The first goal of the dissertation is to devise an active control strategy that overcomes this problem. A novel scheme based on the concept of locally altering the resin viscosity in real time, in areas of low permeability, is explored both numerically and experimentally, by considering the VARTM process.^ A second focus of the dissertation is on the fabrication of composites with carbon nanotube reinforcements. Effective design and engineering of the process requires fundamental information on the chemorheology and the cure kinetics of the reactive resins filled with carbon nanotubes. Fundamental information on the cure kinetics and chemorheology is determined for the first time to elucate the role of nano-scale reinforcements, their morphology, and geometry on the viscosity and cure reaction rate.^ The interface between the carbon nanotubes and the surrounding resin has been the subject of much attention in the literature. Effective load transfer requires a good nanotube/resin interface, which has generally been a challenge to realize. The generally weak interface, however, is attractive for applications of composites that require excellent damping properties of the structures. A systematic experimental study of the effects of carbon nanotube morphology, loading, geometry and the processing of composites with these reinforcements on the damping characteristics is presently lacking, and the third objective of the dissertation is to fill this void.^ Overall, this dissertation makes fundamental advances in the processing of composites with micron- and nano-scale reinforcements. ^