Modern technologies—from shock absorbers and energy-efficient machinery to advanced robotics—depend on materials that can efficiently store and release mechanical energy. This essential process involves converting motion or mechanical work into elastic energy, which can later be recovered and reused. At the core of this transformation is enthalpy, a key measure of how much energy a material can absorb and release. Yet maximizing enthalpy remains a significant engineering challenge. According to Professor Peter Gumbsch of the Karlsruhe Institute of Technology (KIT), the difficulty lies in balancing often conflicting properties: high stiffness, high strength, and large recoverable strain.

To overcome this, Gumbsch—who also directs the Fraunhofer Institute for Mechanics of Materials in Freiburg—collaborated with researchers from China and the United States to develop an innovative mechanical metamaterial. These are materials with engineered internal structures that do not exist in nature, granting them extraordinary properties. The team’s starting point was deceptively simple: a round rod. They discovered a way to store large amounts of elastic energy in it without breaking or causing permanent deformation. By cleverly arranging these rods, they integrated the mechanism into a full-scale metamaterial.

Unlike conventional bending springs, which suffer from stress concentration on their outer surfaces and limited durability, the researchers found that twisting the rod distributed stress more evenly and reduced underutilized interior volume. They applied extreme torsion to the rods, inducing a helical buckling pattern that maximized energy retention while maintaining structural integrity. Incorporating these twisted rods into a larger metamaterial, they created a structure capable of handling uniaxial loads on a macroscopic level.

Computer simulations and laboratory experiments confirmed the metamaterial’s impressive performance. Not only did it exhibit high stiffness and energy absorption, but it also achieved enthalpy levels 2 to 160 times greater than previously reported in other metamaterials. These findings were further validated through compression tests on samples with mirrored chiral structures, which enabled the material to deform elastically while maintaining its energy-storing properties.

According to Gumbsch, this new metamaterial holds vast potential for a range of high-performance applications. It could be used in shock absorbers, vibration dampers, flexible robotic joints, and components in energy-efficient machinery. Additionally, the internal twisting mechanism could serve as a foundation for purely elastic joints, offering long-lasting flexibility without wear.

This pioneering work not only establishes a new benchmark for mechanical energy storage in engineered materials but also paves the way for smarter, more efficient systems in fields where performance, resilience, and sustainability are increasingly essential.

By Impact Lab