What do a flea and an eagle have in common? They can store energy in their feet without having to continuously contract their muscles to then jump high or hold on to prey. Now scientists Now scientists at Queen Mary University of London and University of Cambridge have created materials that can store energy this way, be squeezed repeatedly without damage, and even change shape if necessary. These kinds of materials are called auxetics and behave quite differently from regular materials. Instead of bulging out when squeezed, they collapse in all directions, storing the energy inside.
Current auxetic material designs have sharp corners which enable them to fold onto themselves, achieving higher density. This is a property that has been recognised recently in lightweight armour designs, where the material can collapse in front of a bullet upon impact. This is important because mass in front of a bullet is the biggest factor in armour effectiveness. The sharp corners also concentrate forces and cause the material to fracture if squeezed multiple times, which is not a problem for armour as it is only designed to be used once.
In this study, published in Frontiers in Materials, the team of scientists redesigned the materials with smooth curves which distribute the forces and make repeated deformations possible for other applications where energy storing and shape-changing material properties are required.
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