Beyond hyperelasticity: a virgin land of extreme materials

Beyond bifurcation, beyond instability, beyond even hyper-elasticity (!) there is an unexplored world of superior materials, capable of introducing a high-tech revolution and even influencing our daily lives. Surpassing bifurcation and instability yields unprecedented deformational capabilities and going beyond the concept of the elastic potential leads to materials capable of absorbing energy from the environment in a closed cycle of deformation and releasing it upon request. The road to this new paradigm is the fusion of the concepts of structural mechanics with the principles of solid mechanics, both brought to the highly nonlinear realm of extreme deformation. This opens virgin territory, left unexplored since the 100-years-old definition of the elastic potential, which has been treated until now as inviolable dogma. But structural engineers know structures capable of harvesting energy from the wind or becoming dynamically unstable when subject to follower loads, so that the implantation of these structural concepts in microscale form into a macroscopic solid leads to the creation of materials surpassing the concept of elastic potential and opening new horizons in the design of new materials. Our recent work exhibited that a purely elastic and conservative system can experience flutter instability. This strongly implies that an elastic solid can be devised that will exhibit this instability and violates hyper-elasticity. Implementing these concepts at the microscale (with elements generating microscopic interactions to suck/deliver energy from/to external sources) leads to architected materials which may harvest energy, or release it to move a mechanism, or propagate a signal with amplification, or suffer a Hopf bifurcation and self-oscillate at designed frequency. This is an unexplored field where we expect applications in metamaterials, locomotion devices, wearable technologies, sensors, or interacting devices for use in everyday life and medical applications.