University of Scotland
Researchers from universities in Scotland and Italy have develop a 3D printed twisting metamaterial that they believe could lead to improved crash protection for vehicles.
The metamaterial has been designed to mitigate the effects of impact, with a unique lattice shape twisting itself 'like a corkscrew' to effectively protect against a range of impact types and severities.
Made from steel and processed using additive manufacturing, researchers from the University of Glasgow, Polytechnic University of Marche, the University of L’Aquila and the National Institute for Nuclear Physics in Italy have fine-grained control over the material's architecture. It allows, the researchers say, a complex and highly porous gyroid lattice to be weaved.
It means that, unlike conventional foams or crumple zones which provide predetermined resistance to impacts, the material's response to impact can be mechanically controlled, altering its energy absorption. The response to impact can therefore be fine-tuned to provide stiffer resistance to heavy collisions or softer cushioning for lighter impacts.
The team of researchers has tested three versions of the material to assess their response to rapid impacts and slower, steadily increasing strains. When the metamaterial was constrained from twisting in response to impacts, it provided maximum stiffness and absorbed the most energy - 15.36 joules of energy per gram of the material. When the material was allowed to twist freely instead, its stiffness and energy absorption decreased by approximately 10 percent. In the material’s third configuration, it was forced to over-twist, reducing energy absorption by 33 percent.
The results show that the material has the potential to provide a range of protection, from rigid shielding to softer energy absorption. They are supported by a comprehensive theoretical and computational model which can accurately predict the complex behaviour of twisting gyroid lattices under different strain rates. For accurate numerical–experimental alignment, geometric imperfections introduced during additive manufacturing were quantified by integrating micro-CT reconstructions of the printed lattices.
Professor Shanmugam Kumar of the University of Glasgow’s James Watt School of Engineering led the research. He said: “The protective materials used in most vehicles today are static, designed for specific impact scenarios and unable to adapt to varying conditions. This study introduces adaptive twisting metamaterials as a new class of metamaterials that don’t require any complex electronics or hydraulics to adapt. Instead, they can adapt simply through mechanical control of rotation. When we apply compression, the gyroid lattice translates it into twist, and by changing the boundary conditions, we can tune the energy absorption characteristics. These materials can adapt and change their own characteristics depending on the impact type and severity to mitigate effects.
“We believe the material could find applications in both automotive and aerospace safety in the future, providing a single new class of material capable of adapting to different needs as required. It could also support the development of novel forms of energy harvesting, by converting impacts into rotational kinetic energy.”
The team’s ‘adaptive twisting metamaterials’, outlined in a paper published in the journal Advanced Materials, take a different approach to impact protection materials currently in use. Researchers from the Polytechnic University of Marche, the University of L’Aquila and the National Institute for Nuclear Physics in Italy contributed to the research and co-authored the paper. The team’s paper, titled ‘Adaptive Twisting Metamaterials’, is published in Advanced Materials.
