Variable Stiffness and Variable Size Particles for Reconfigurable Granular Metamaterials

Soft robots can achieve exceptional adaptability through tunable morphological and mechanical properties. Incorporating materials with dynamically adjustable characteristics can enhance this versatility further. Granular meta-materials, consisting of discrete particles with individually variable properties, offer a promising approach to bulk property adaptation by adjusting the properties of constituent particles. This work introduces variable size and variable stiffness (VS<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>) particles, in which both particle size and stiffness are independently modulated through concentric pneumatic chambers. We characterize the achievable workspace, mapping particle responses to independent chamber inflation. To demonstrate their use in a granular assembly, we arrange an array of VS<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> particles in a hexagonal packing and validate that behavior in packed configurations aligns with free-space characterizations. This study establishes a foundation for adaptive granular materials and provides a platform for further computational and experimental exploration of 2D and 3D granular metamaterials with tunable properties.