Metamaterials: Twisted Rods Store Large Amounts of Energy
New mechanical metamaterials developed at KIT exhibit high stiffness and high elastic energy density
An international team of researchers coordinated at the Karlsruhe Institute of Technology (KIT) has developed mechanical metamaterials with a high elastic energy density. Thanks to highly twisted rods that deform in a spiral, they exhibit high rigidity and can absorb and release large amounts of elastic energy. The researchers confirmed their initially theoretical results with simple pressure experiments. They report their findings in the journal Nature.
The model shows the spiral deformation of the metamaterial. Thanks to this mechanism, a large amount of energy can be stored without fractures occurring.
IAM, KIT / Collage: Anja Sefrin, KIT
Whether springs for energy absorption, buffers for energy storage, but also flexible structures in robotics or in energy-efficient machines: many technologies require mechanical energy storage. Kinetic energy, i.e. kinetic energy, or corresponding mechanical work is converted into elastic energy in such a way that it can be completely released again when required. The key parameter for this is enthalpy - the energy density that can be stored and recovered in a material element. Peter Gumbsch, Professor of Materials Mechanics at the Institute for Applied Materials (IAM) at KIT, explains the challenge of achieving the highest possible enthalpy: "The difficulty lies in combining contradictory properties: high stiffness and high recoverable deformation with limited strength."
Spirally deformed rods are cleverly arranged in metamaterials
Artificially designed materials that do not occur in nature, so-called metamaterials, make it possible to adapt effective material properties, as they can be constructed from individually determined units. Peter Gumbsch, who also heads the Fraunhofer Institute for Mechanics of Materials IWM in Freiburg, has now succeeded in developing mechanical metamaterials with a high recoverable elastic energy density as part of an international research team from China and the USA. "First, we discovered a mechanism that allows a large amount of energy to be stored in a simple round rod without it breaking or permanently deforming," says Gumbsch. "We then integrated this into a metamaterial by cleverly arranging the rods."
The scientists describe the mechanism using the functionality of a classic bending spring. This is limited in its maximum deformation by the fact that high tensile and compressive stresses occur on the upper and lower sides, which lead to breakage or permanent plastic deformation. In such a bending spring, the entire inner volume is only slightly stressed. However, if a rod twists instead, the entire surface is also subject to high stresses, but the unloaded volume inside is much smaller. However, in order to really be able to use this mechanism, the torsion must be so great that it leads to a complex spiral deformation.
Enthalpy is two to 160 times higher than with other metamaterials
The researchers have succeeded in integrating such torsionally loaded and spirally deformed rods into a metamaterial that can be used macroscopically under uniaxial loads. Based on simulations, they predicted that the metamaterial has a high stiffness and can therefore absorb large forces. It also has an enthalpy two to 160 times higher than other metamaterials. They confirmed this with simple pressure experiments on various chiral metamaterials, i.e. metamaterials with mirror-image structures.
"Our novel metamaterials with high elastic energy storage capacity could be used in the future in various areas where efficient energy storage and exceptional mechanical properties are required," says Gumbsch. In addition to energy storage in springs, shock absorption or damping as well as flexible structures in robotics or in energy-efficient machines are also conceivable. The rotations that occur inside the metamaterials could also be used in purely elastic joints.
Note: This article has been translated using a computer system without human intervention. LUMITOS offers these automatic translations to present a wider range of current news. Since this article has been translated with automatic translation, it is possible that it contains errors in vocabulary, syntax or grammar. The original article in German can be found here.
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