Carbon Nanofiber-Network Sensor Films for Strain Measurement in Composites

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Carbon Nanofiber-Network Sensor Films for Strain Measurement in Composites

Nguyen Quang Nguyen, Sangyoon Lee, and Nikhil Gupta Composite Materials and Mechanics Laboratory Mechanical and Aerospace Engineering Department Polytechnic Institute of New York University Brooklyn, NY 11201 Phone: 718-260 3080, Fax: 718-260 3532, Email: [email protected] ABSTRACT A carbon nanofiber-based sensor film is designed and calibrated for force measurement. The sensor is designed for use in structural health monitoring of composite materials. The sensing scheme is based on creating a network of carbon nanofibers on the surface of the composite material. In the experimental scheme a patch of nanofiber reinforced epoxy resin film is developed and adhesively bonded to the laminate. The extension of the sensor film due to the applied force leads to a change in the connectivity of carbon nanofibers in the film, resulting in the change in the resistance of the network. Results show that such sensing schemes have high sensitivity and repeatability. Use of nanofibers can provide a low cost and more efficient alternative to other sensor films that rely on carbon nanotubes. INTRODUCTION Carbon nanotube based sensors are being explored in the recent years [1, 2]. In nanostructures electron transport through one nanotube and through the network are significant issues [3]. In addition contact resistance plays a dominating role because of losses at each junction. Some of these effects can be reduced if the conducting network is made of high aspect ratio structures, having fewer connections but still very high surface area. Carbon nanofibers (CNFs), which possess mechanical and electrical properties similar to those of carbon nanotubes (CNTs), are cylindrical nanostructures with stacks of graphene layer perpendicular to the nanofiber axis [4]. Compared to carbon nanotubes, CNFs are much cheaper than the multiwalled or single-walled carbon nanotube [5]. Therefore, carbon nanofibers are used in the present study to explore the possibility of developing nanofiber network based sensing schemes. Structural health monitoring techniques based on CNF sensors have potential application in civil, mechanical, and aerospace systems [6]. CNFs have been extensively used as biosensor and gas sensors in published studies [4, 7-9]. However, their application in force, displacement or temperature sensors are not yet fully developed despite having great potential in this area. Normally the nanotube/nanofiber networks are connected to the electrical measurement systems using conductive silver paint. However, the properties of the adhesive paint in bonding the electrodes with the network dominate the measurement accuracy. In our sensors we expect displacements of the order of several mm. At this displacement scale the measurements are observed to have significant fluctuations, resulting in loss of sensitivity. In present work embedded electrodes are used to improve the connection quality to obtain consistent measurement of resistivity.

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