Composite for safer cars

Anthony King

A new composite made of organic polymers and carbon nanotubes is tougher and lighter than similar forms of aluminium alloys.

The 3D printed material could allow the development of safer, lighter and more durable structures for use in aerospace, automotive, renewable and marine industries, say engineers at the University of Glasgow, UK (Materials and Design, 2021, 202, 109516).

The researchers mixed either polypropylene or polyethylene with multi-wall carbon nanotubes. They varied the quantity of carbon nanotubes, but also tried out plate-lattice structures in various cubic designs. Lattice structures are cellular architectures, like the Eiffel Tower, made up of numerous individual elements, with the goal to form a lightweight yet mechanically robust system, explains Jens Bauer, a materials engineer at the University of California, Irvine, US, who was not involved in the research.

Plate-lattices are unusually lightweight, yet potentially tough. The team 3D printed and then tested various lattice structures for impact resistance by dropping a 16.7kg mass from various heights. The hybrid design that proved most robust incorporated all three typical plate-lattice designs, with the polypropylene version showing the best performance.

‘It is not only the properties of the constituents present in the materials,’ says materials engineer Shanmugam Kumar at the James Watt School of Engineering, University of Glasgow. ‘But also the geometrical structure of the lattice that we created which brings extraordinary performance.’

One application would be cars, says Kumar. Car designers constantly try to build more lightweight vehicles, without sacrificing safety. Aluminium is used in many car designs, but Kumar says the team’s plate-lattice design boasts greater impact resistance. He is in talks with a composite manufacturer in the US.

Adding carbon nanotube structures to the composite also makes it responsive to changes in mechanical load, which alters the material’s electrical resistance, says Kumar. This in turn can be related to ‘the structural health of the component,’ meaning that the composite can sense damage.

‘The most promising application of such materials could be lightweight structural parts,’ notes Bauer, adding that a downside is the complexity in manufacturing such components. ‘Today plate-lattice fabrication is mostly limited to additive manufacturing and not feasible on an industrial scale.’

‘The paper provides an important experimental comparison of the mechanical behaviour of different plate-lattice construction types, which is much needed to further develop the research field,’ he says.

His research group at Irvine recently demonstrated plate-lattices made from nanoscale carbon (C&I, 2020, 84, (5), 9). These are ‘the only reported material to reach the theoretical strength and stiffness limits, out-performing diamond, the strongest known bulk solid, while consisting of more than 50% air’.