Research promises to lead to better composite materials

A team of researchers has created new composites by stacking layers of ceramic cloth with interlocking nano-tubes that provide "remarkable improvements " in strength and toughness compared to traditional materials.

The scientists believe that the "nano-tube sandwiches", which are described in the 7 May online edition of the journal Nature Materials, could find uses in a wide array of structural applications.

"Nano-tubes are a very versatile material with absolutely fascinating physical properties, all the way from ballistic conduction to really interesting mechanical behavior," said Pulickel Ajayan, the Henry Burlage professor of materials science and engineering at Rensselaer, and a lead author of the paper along with colleagues at the University of Hawaii at Mānoa.

For their current project, the researchers are applying the process to a new area: reinforced composite fabrics made from woven ceramic fibers.

These materials have been used for decades in structural applications, but tend to perform poorly in terms of "through-thickness", or the ability of a material to respond to forces applied perpendicular to the fabric-stacking direction.

"We have demonstrated that these through-thickness properties can be improved by adding nano-tube Velcro-like structures between the layers," said Mehrdad Ghasemi-Nejhad, professor of mechanical engineering at Hawaii and a lead author of the paper.

To make the new materials, the researchers deposited a forest of carbon nano-tubes across the surface of a cloth woven from fibres of silicon carbide, a ceramic compound made from silicon and carbon.

The fabric layers are infiltrated with a high-temperature epoxy matrix, and then several layers of cloth are stacked on top of each other to form a 3D composite sandwich with interlocking nano-tubes acting to fasten the layers together.

"This is a very nice example of how to use nano-tubes to solve major existing problems, rather than going all-out to make composites based on nano-tubes alone, which has proven to be a very challenging task," said Ajayan.

The team has successfully made cloths up to roughly five inches by two inches, and the process is easily scalable to make larger materials.

The researchers ran several experiments to test the new material's properties, and found that the interlocking nano-tubes provided substantial improvements in strength and toughness under various loading conditions.

The materials performed extremely well in fracture tests, and demonstrated a five-fold increase in damping - or the ability to dissipate energy - over the original ceramic composites without nano-tubes included.

This suggests that the new composites could be used in many applications where mechanical properties are important, from automobile engines to golf club shafts.