Lab talk
Nov 16, 2011
Nanocomposites provide early warning against failure for next generation aircraft
Recent developments in aircraft design, as evidenced by Bombardier C-series, Airbus A380 and Boeing B787 airliners, have led to a dramatic rise in the use of composites and a corresponding increase in adhesive bonding of primary structures in aircraft. Primary structures carry primary flight loads and their failure would result in a loss of aircraft. Unlike mechanical fastening or welding, structural adhesive bonding is often the most attractive joining technique for similar/dissimilar composites and metals. This is because mechanical fasteners introduce localized stresses and welded joints suffer from possible phase transformation, undesirable tensile residual stresses and inclusions in the weld region. On the contrary, adhesive bonding offers substantial weight reduction, low bonding temperature and uniform stress transfer instead of highly localized point contacts in mechanical fastening. It is with this in mind that researchers have teamed up to undertake a strategic research initiative.
The team, led by Shaker Meguid from the Mechanics and Aerospace Design Lab at the University of Toronto, Canada, is interested in converting polymeric thermoset adhesive resins into multifunctional materials that performs multiple "structural" and "non-structural" functions simultaneously. The multifunctionality will be achieved via the dispersion of very small amounts (for example, concentrations of 0.1–2%) of carbon nanotubes and nanowires.
Crack monitoring
In their work, the multifunctionality of the adhesive resin will be manifest in the significant improvement in the electro-mechanical properties. The resulting tailored properties will have a significant impact on the ability to self-health monitor an aircraft's primary structures for cracks, delamination and other sources of failure.
The development of such smart adhesives for use in future aircraft will provide early warning of impending catastrophic failures in primary structures. The group is currently investigating the effect of uniformly dispersed, aligned and agglomerated carbon nanotubes on the electrical conductivity of multifunctional nanocomposites. Unlike earlier Monte Carlo simulations, the current work employs a novel network recognition approach to determine current continuity and critical percolation level. The researchers employed periodically connective paths and these led to the reduction of the finite size of the representative volume element that contains the carbon nanotubes (CNTs).
Design tool
The results of their study, which are in good agreement with existing experimental work, reveal that the highest electrical conductivity occurs when the CNTs are partially rather than perfectly aligned. The data further shows that the presence of agglomerated CNTs results in a higher conductivity at and close to the percolation threshold, but limits the increase in the electrical conductivity of the nanocomposite with increased fractions of CNTs.
The group's results provide a new, robust and computationally efficient model that can be adopted as a predictive tool to characterize and evaluate electrical conductivity in multifunctional nanocomposites.
Further details can be found in the journal Nanotechnology.
About the author
The research into multifunctional nanocomposites is being conducted by engineers from the Mechanics and Aerospace Design Lab at the University of Toronto. The team includes Jake Wernik (PhD student), Ben Cornwell-Mott (PhD student), Dr Wei Shun Bao (postdoctoral fellow) and Prof. S A Meguid, who is director of the lab. The work published recently in Nanotechnology is funded by the Natural Sciences and Engineering Research Council of Canada (NSERC) and is also part of a collaborative research project funded by the Qatar National Research Fund (QNRF) under agreement NPRP 09-508-2-192. This nanoengineering collaborative research effort, led by Prof. S A Meguid, involves professors G Weng of Mechanical and Aerospace Engineering at Rutgers University, Harry Ruda of the Department of Metallurgy & Material Science at the University of Toronto, Prof. George Zhu of the Department of Earth and Space Science and Engineering at York University and Prof. A M S Hamouda of the University of Qatar. Dr Bao, a postdoctoral fellow at the University of Toronto, conducted the percolation analysis, which was guided closely by professors Meguid and Zhu, with input from Jake Wernik and Ben Cornwell-Mott.
