Mechanical properties of blended single-wall carbon nanotube composites
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G.M. Pharr Materials Science and Engineering Department, University of Tennessee, Knoxville, Tennessee 37996
B. Files ES4-Materials and Processes Branch, NASA/Johnson Space Center, Houston, Texas 77058 (Received 3 February 2003; accepted 9 May 2003)
The improvement in mechanical properties of blended nanocomposites prepared using a low-viscosity, liquid epoxy resin and purified single-wall carbon nanotubes (SWCNTs) was evaluated. The macroscopic tensile stress–strain behavior for hybrid materials made with varying amounts of SWCNT was determined and showed little improvement in the breaking tensile strength. The corresponding variations in modulus and hardness were obtained using nanoindentation considering time effects and showed quantifiable but modest improvements. The small changes in the observed stiffness and breaking strength of carbon nanotube composites is due to the formation of bundles and their curvy morphology.
I. INTRODUCTION
In 1985, a new form of carbon, buckministerfullerene C60, was discovered by Smalley and coworkers at Rice University.1 C60 is a geometric cagelike structure of pure carbon atoms bonded in hexagon and pentagon configurations. Besides diamond, graphite, and C60, the quasione-dimentional nanotube is another form of carbon, first reported by Iijima in 1991 when he discovered multiwalled carbon nanotubes in carbon soot made by the arc-discharge method.2,3 About two years later, observations of single-wall carbon nanotubes (SWCNTs) were made.4 Since then, the SWCNTs have stimulated great interest in various scientific communities.5,6 A significant amount of work was done in the past decade to reveal the unique structural, electrical, mechanical, electrochemical, and chemical properties of individual carbon nanotubes. Nanotubes are long, slender fullerenes where the walls of the tubes are hexagonal carbon (graphite structure) and often capped at each end. The carbon nanotubes have been shown to exhibit exceptional material properties that are a consequence of their symmetric structure. Many researchers have reported mechanical properties of carbon nanotubes that exceed those of any previously existing materials. Although there are varying reports in the literature on the exact properties of carbon nanotubes, theoretical and experimental results have shown extremely high elastic modulus, greater than 1 TPa (the elastic modulus of diamond is 1.2 TPa) and reported strengths 10–100 times higher J. Mater. Res., Vol. 18, No. 8, Aug 2003
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than the strongest steel at a fraction of the weight. In addition to the exceptional mechanical properties associated with carbon nanotubes, they also possess superior thermal and electric properties: thermally stable up to 2800 °C in vacuum, thermal conductivity about twice as high as diamond, and electric-current-carrying capacity 1000 times higher than copper wires.7 These exceptional properties of carbon nanotubes have led to an explosion of research efforts worldwide. The chirality of the carbon
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