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AFRL TO #14 - Modeling and Simulation of SWNT Buckypaper Electrical Conductivity
Objective and Background
This resCNT thin film schematicearch seeks to develop computational simulations to model the electrical conductivity from steady-state current loadings of macro-scale networks of neat carbon nanotubes (CNT) (also referred to as buckypapers), and to capture, in a concise numerical model, the dependency bulk conductivity has on stochastic nanoscale effects. As it is understood, the AFRL’s objective in conductivity simulations is to provide insight into the possible employment of a nanostructured composite as a multifunctional materials system to improve or replace current lightning strike protection systems. The work incorporated results from the literature for nano-scale properties and developed a predictive methodology for the resulting conductivity of neat carbon nanotube thin films. The work sought to address a significant challenge that could only be satisfied through stochastic computations due to the consideration of the full length scale range for each of the relevant physical phenomena and parameters involved in nanotube conducting networks. Case studies were presented to better understand the dependence of bulk conductivity on nanoscale parameters such as such as orientation, density of packing, aspect ratio distribution, bundle size, volume fraction, etc. In addition, several studies were presented to investigate possible network failure mechanisms. A case study was developed to demonstrate a possible application of the results that studies a quasi-static failure of a CNT thin film placed on a polymer substrate, and couples the resistive heating failure with that of the substrate thermal heating. The research has yielded a fully three dimensional network simulation suite for linear, quasi-static loadings. Results are presented for both the preliminary 2D model aVoltage drop across the CNT thin filmnd the recently developed 3D model for a variety of case studies. The trends between the two approaches are similar for the expectation of the conductivity, but the sensitivity to stochastic inputs between the two approaches is different. A discussion was presented to explain the limitations from a 2D approximation and to justify the need for a fully three dimensional model. Future work should focus on the coupled thermal/electrical problem and will need to address the non-linear effects observed from rapid changes in the current loading characteristics as observed from a real-world lightning strike.

Developed Results
  • Developed 2D, 2.5D and 3D network models, and presented evidence for the failure of the 2D and the 2.5D models to properly account for the stochastic behavior of the electrical conductivityThermal heating of CNT on a resin substrate near CNT film failure
  • Provided studies for the conductivity as a function of length and diameter
  • Provided studies to validate the constructed physics based model based on experimental observations provided in the literature
  • Provided a short study for quasi-static failure of the network, and coupled the nanoscale results with a continuum based finite element model on a resin substrate, and results corresponded quite well with experimental results in the literature
Publications From This Work
  • Electrical Conductivity Modeling and Experimental Study of Densely Packed SWCNT Networks. D.A. Jack, C.-S. Yeh, Z. Liang, S. Li, J.G. Park, and J.C. Fielding. Nanotechnology, 21(19):195703-12, 2010.
  • Stochastic Modeling of the Bulk Thermal Conductivity for Dense Carbon Nanotube Networks. N. Ashtekar* and D.A. Jack. Proceedings of ASME IMECE'09, Orlando, Florida, November, 2009.
  • Statistical Planar Conductivity Modeling of Carbon Nanotube Network Buckypapers. D.A. Jack, R. Liang*, S. Li, J. Fielding, SAMPE'09, Baltimore, MD, May 2009.
Baylor University School of Engineering and Computer Science Department of Mechanical Engineering Sic'Em - Scientific Innovations in Composites and Engineering Materials