Mechanical Properties of Carbon-Nanotube Ceramic Matrix Composites
William A. Curtin, Division of Engineering, Brown University, Providence, RI
Co-sponsored by: Mechanical, Aerospace and Nuclear Engineering and Materials Science and Engineering
Wed, June 4, 2003, 3:30pm - 4:30pm, CII 3112
Abstract: The excellent mechanical properties of carbon-nanotubes are driving research into the creation of new strong, tough nanocomposite systems. Here, the first evidence of toughening mechanisms operating in carbon-nanotube-reinforced ceramic composites is presented. A highly-ordered array of parallel multiwall carbon-nanotubes (CNTs) in an alumina matrix was fabricated. Nanoindentation introduced controlled cracks and the damage was examined by SEM. These nanocomposites exhibit the three hallmarks of toughening in micron-scale fiber composites: crack deflection at the CNT/matrix interface; crack bridging by CNTs; and CNT pullout on the fracture surfaces. Interface debonding and sliding can thus occur in materials with microstructures approaching the atomic scale. Furthermore, for certain geometries a new mechanism of nanotube collapse in "shear bands" occurs, rather than crack formation, suggesting that these materials can have multiaxial damage tolerance. Evidence for a novel nanotube fracture mode is also presented. The quantitative indentation data and computational models are used to determine the multiwall CNT axial Young's modulus as 200-570 GPa, depending on the nanotube geometry and quality. 3d FEM analysis indicates that matrix residual stresses on the order of 300 MPa are sustained in these materials without spontaneous cracking. Overall, these results show that careful tailoring of the nanotube geometry (diameter, wall thickness), matrix properties, and residual stresses, may permit engineering of these materials for multiaxial hardness and damage tolerance at submicron scales, making them excellent candidates for wear-resistant coatings.
Biography: Dr. William Curtin received a combined 4 yr. ScB/ScM degree in Physics from Brown University in 1981 and a PhD in theoretical physics from Cornell University in 1986, working under Professor N. W. Ashcroft on the optical properties of metal nanoparticles and on statistical mechanics theories of freezing. Dr. Curtin then joined the Applied Physics Group at the British Petroleum Research Laboratories (formerly SOHIO) in Clevelend, OH, where he worked on hydrogen storage in amorphous metal alloys, the statistical mechanics of crystal/melt interfaces, and the mechanics of monolithic ceramics, fibers, and ceramic and metal matrix composites. In 1993, he joined the faculty at Virginia Tech with a joint appointment in Materials Science & Engineering and Engineering Science & Mechanics. In 1998, Professor Curtin returned to Brown University as a faculty member in the Solid Mechanics group of the Division of Engineering. A current overall theme of Professor Curtin's research is multiscale modeling of the mechanical behavior of materials, with specific applications to fiber composites, atomistic/continuum models of plasticity and fracture, fracture in micro/nano lamellar Titanium Aluminides, solute hardening in aluminum alloys, and impurity/defect diffusion. Other current work includes experiments and modeling of carbon-nanotube-based ceramic composites, electrical sensing of damage in polymer composites, mechanics of complex microstructures, and crystal plasticity models of deformation in aluminum.For further information, contact Debbie McCann (518) 276-3239.