Topologically reconfigurable mechanical metamaterials with motion structures

Motion structures whose macroscopic topology can be controlled by an internal kinematic mechanism play a new role in the design of mechanical metamaterials. Motion structures with N-fold symmetry show a reconfigurable pattern transformation, providing tunable mechanical properties by topological reconfiguration, not by geometric reconfiguration. The objective of this work is i) to synthesize motion structures from a bar-andjoint framework and ii) to investigate their mobility and symmetry breaking during transformation together with nonlinear structural properties - modulus and Poisson's ratio, switchable stiffness, and bi-stiffness. Two-dimensional (2D) motion structures with N-fold symmetry (MS-N) are synthesized by central scissor links with revolute joints, connected with binary links in the radial direction. Five 2D motion structures - MS-4, MS-6, MS-8, MS-10, and MS-12, are constructed for investigating their mechanical properties together with their transformability. We build analytical models of motion structures on relative density, modulus, Poisson's ratio, and switchable stiffness as a function of transformation, verified with experiments and numerical simulations. By combining the kinematic mechanisms with structural mechanics, this study contributes to expanding the design space of reconfigurable metamaterials.