Semester

Spring

Date of Graduation

2006

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Lane Department of Computer Science and Electrical Engineering

Committee Chair

Powsiri Klinkhachorn.

Abstract

Most neat resins, including thermoplastics and thermosets are electrical insulators. However, conductive additives or fillers (such as carbon black, carbon fibers) can be added into resins to produce electrically conductive resins and composite materials. At a specific concentration of conductive filler, electroconductive channels are formed and the insulators are turned into semi-conductors. This transformation process can be described within the framework of the percolation theory. The objective of the present study is to develop conductive polymer composites as sensors in terms of change in their electrical resistance as a function of deformation and other parameters for health monitoring and structural response detection of wide range of structural systems including air and spacecraft structures and in particular, fiber reinforced polymer (FRP) composites structures.;Researchers at CFC-WVU have developed a smart material system by adding nanomaterials to neat resins to produce conductive composite sensors (WVU patent pending). The operation of a conductive nanocomposite sensor system is based on the phenomenon that the electrical conductivity of the composite material system changes when exposed to an external stimulus. The change in conductivity/resistivity can be correlated quantitatively to the intensity of external stimulus. Preliminary evaluation demonstrates that the composite sensor developed by CFC-WVU researchers appears to be able to detect changes in moisture and strain under mechanical loading in real time. The axial sensitivities SA of the conducting composites were in the range of 5-15 for different variations in the constituent materials. This is very good considering that the SA for common strain-gage alloys are in the range of 2-5. The smart material has good thermal stability and is not influenced appreciably by temperature changes up to 130 F. Moisture has an effect (the resistance of the sample increases with increase in moisture and vice versa) on the resistance of the material. This is a limitation since we have to use a correction factor depending on the amount of moisture and the time of exposure at that particular humidity level. The resistance of the material over prolonged period of time, the effect of harsh environment (material degradation), durability have to be further investigated.;The CFC-WVU composite sensor has a great potential. It can be designed at any desired scale (dimensions) and manufactured economically. Those sensors can either be embedded into a system during manufacturing or can be grafted onto the surface of a structural component. Moreover, such a sensor can be designed and produced with electrical signal transmission capability, allowing for wireless measurements of material property changes.

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