Transformative elastic metamaterials: Temperature-induced passband-to-bandgap conversion

Elastic metamaterials favor the wide bandgap generation, but their formation mechanisms impose certain constraints on the achievable locations and widths. To overcome this limitation, this study proposes an innovative method that optimizes specific passbands and subsequently transforms them into bandgaps through an external stimulus. As an illustration, two meta-beams with different third passbands are optimized. In addition, to examine the formation and transformation mechanisms of the optimized passbands, this study develops several meta-beam models, incorporating force neutralizers, moment neutralizers, and their hybrid combinations, which are modally equivalent to the optimized unit cells. Samples for the two optimized meta-beams are fabricated using a three-dimensional printing technique. The experimental measurements are conducted at both room temperature and elevated temperatures, and the results confirm that when the temperature increases to approximately 60 degrees C, the optimized third passbands transform into bandgaps. Furthermore, repeated thermal loading cycles substantiate the reversibility of this transformation, demonstrating a promising application potential of the proposed method to tunable broadband meta-beam designs.