Harnessing instabilities within metamaterial structures

Advances in additive manufacturing are increasingly allowing bespoke, carefully designed, metamaterial lattice structures to be constructed for enhanced mechanical performance. For instance, in structural elements that are designed to absorb energy and shield a more valuable structure, the properties combining a high initial stiffness followed by a practically zero underlying stiffness, ensure that a desired energy quantity may be absorbed within a limited displacement and that any stress transfer to the valuable structure is minimized. Presently, a lattice structure is studied that is deliberately designed to switch locally under compression between conventional material behaviour to that exhibiting auxetic (negative Poisson’s ratio) behaviour through a sequence of snap-through instabilities within layers of individual lattice cells. The sequence of buckling instabilities can potentially be controlled to maintain the loading level alongside the low structural stiffness while the required energy quantity is absorbed, without necessarily damaging the material in the process. This departs from the usual paradigm where such structures are presently designed to be sacrificial and opens up the intriguing possibility of introducing such structural elements that are repairable and therefore reusable.