An international team of engineers has developed a new lightweight, 3D-printed smart architected material inspired by the cellular forms of natural porous materials such as beehives, sponge and bone, which are lightweight but robust.
The team, led by engineers from the University of Glasgow, mixed a common form of industrial plastic with carbon nanotubes to create a material that’s tougher, stronger and smarter than comparable conventional materials.
The nanotubes also allow the otherwise non-conductive plastic to carry an electric charge throughout its structure. When the structure is subjected to mechanical loads, its electrical resistance changes. This phenomenon, known as piezoresitivity, enables the material to ‘sense’ its structural health.
By using advanced 3D-printing techniques that provide a high level of control over the design of printed structures, the engineers were able to create a series of intricate designs with mesoscale porous architecture, which helps to reduce the overall weight and maximise mechanical performance. They believe that their cellular materials could find new applications in medicine, prosthetics and automobile and aerospace design, where low-density, tough materials with the ability to self-sense are in demand.
The researchers investigated the energy-absorbing and self-sensing characteristics of three different nanoengineered designs that they printed using their custom material, which is made from polypropylene random co-polymer and multi-wall carbon nanotubes. They found that a cube-shaped ‘plate-lattice’ that incorporated tightly packed flat sheets exhibited the most effective combination of mechanical performance and self-sensing ability.
The lattice structure, when subjected to monotonic compression, shows an energy-absorption capacity similar to nickel foams of the same relative density. It also outperformed a number of other conventional materials of the same density.
‘Nature has a lot to teach engineers about how to balance properties and structure to create high-performance lightweight materials,’ said Shanmugam Kumar from the University of Glasgow’s James Watt School of Engineering. ‘We’ve taken inspiration from these forms to develop our new cellular materials, which offer unique advantages over their conventionally produced counterparts and can be finely tuned to manipulate their physical properties.
‘The polypropylene random co-polymer we’ve chosen offers enhanced processability, improved temperature resistance, better product consistency and better impact strength,’ he continued. ‘The carbon nanotubes help to make it mechanically robust while imparting electrical conductivity. We can choose the extent of porosity in the design and architect the porous geometry to enhance mass-specific mechanical properties.
‘Lightweight, tougher, self-sensing materials such as these have a great deal of potential for practical applications,’ Kumar concluded. ‘They could help make lighter, more efficient car bodies, for example, or back braces for people with issues such as scoliosis capable of sensing when their bodies are not receiving optimal support. They could even be used to create new forms of architected electrodes for batteries.’
The research has been published in Advanced Engineering Materials.