Richard J. Johnson

Research Projects

Processing and Performance of Composites with Micro and Nanoscale Reinforcements

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 has been studied in the literature in recent years as 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 situations where only one high quality surface is required. 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 on demand 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 using liquid molding techniques. 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. Significant fundamental information is determined including 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.

Neural Network Aircraft Part Life Model Development

Jet engine parts undergoing cyclic loading often require frequent preventive replacement due to the high probability of fatigue related failure. Neural networks are being explored, as a predictive tool for part life, for situations were the exact physics are difficult to model or measure. Multiple model types, structures, and training methods are being explored systematically to determine a suitable model to ultimately predict part life.

Publications

1. R. J. Johnson and R. Pitchumani, "Induction Heating Assisted Permeation Enhancement for the VARTM Process," in Proceedings of the International SAMPE Technical Conference, 34, 250-261, 2002.
2. R. J. Johnson and R. Pitchumani, "Enhancement of Resin Flow in VARTM Using Localized Induction Heating," Composites Science and Technology, 63, 2201-2215, 2003.
3. R.J. Johnson and R. Pitchumani, "Simulated Active Flow Control in a VARTM Process Using Localized Induction Heating," in Proceedings of the International Conference on Composite Materials, Paper Number: EM03-310, 9 pp., 2002.
4. R.J. Johnson and R. Pitchumani, "Active Flow Control in a VARTM Process Using Localized Induction Heating," in FPCM7: Seventh International Conference on Flow Processes in Composite Materials, S.G. Advani, ed., pp. 247-252, 2004.
5. R.J. Johnson and R. Pitchumani, "Simulation of Active Flow Control based on Localized Preform Heating in a VARTM Process," Composites Part A: Applied Science and Manufacturing, 37(10), 1815-1830, 2006.
6. R.J. Johnson and R. Pitchumani, "Flow Control Using Localized Induction Heating in a VARTM Process," Composites Science and Technology, 67(3-4), 669-684, 2007.
7. R.J. Johnson and R. Pitchumani, "Active Control of Reactive Resin Flow in a VARTM Process," Journal of Composite Materials, 42(12), 1205-1229, 2008.
8. R.J. Johnson and R. Pitchumani, "Localized Induction Heating Based Control of Reactive Resin Flow in the VARTM Process," Invited paper, 9th International Conf. on Flow Processes in Composite Materials (FPCM9), Montreal, Canada, July 2008.
9. R.J. Johnson and R. Pitchumani, "Chemorheology and Cure Kinetics of a Carbon Nanotube Filled Epoxy System," ICCM-17 17th International Conference on Composite Materials, Edinburgh, UK, July 2009, CD ROM Volume, 9 pp.
10. R.J. Johnson and R. Pitchumani, "Characterization of the Rheology and Cure Kinetics of Epoxy Resin with Carbon Nanotubes," Frontiers in Heat and Mass Transfer, 1(1), 013007, 2010.
11. R.J. Johnson, J. Tang and R. Pitchumani, "Characterization of Damping in Carbon-Nanotube Filled Fiberglass Reinforced Thermosetting-Matrix Composites," Journal of Materials Science, 46(13), 4545-4554, 2011

Sponsors