Experimental Studies of Re-Entrant Linear Auxetic Structures (Linear Motion Systems)

Re-entrant structures can be configured into linear mechanical systems that combine the dynamics of unidirectional motion with structural stiffness. Linear technology is defined as a subset of drive and control engineering designed to handle cyclic dynamic loads—including the damping of mechanical vibrations—with high energy efficiency. Transient, repetitive loads are utilized to achieve precise positional changes, ensuring high performance and accuracy. By assembling individual re-entrant unit cells into columns, rigid systems can be created that expand precisely in the perpendicular direction when subjected to tension; the longitudinal and transverse displacements are linked by a negative Poisson's ratio. Such structures are suitable for generating linear mechanical motion along a straight path. The study investigated two versions of re-entrant linear structures designed and fabricated from metal: one based on interconnected torsion springs and another composed of struts connected via hinges to a single extension spring, equipped with guides. The spring-like nature of the structures ensured reversible behavior during stretching and unloading cycles. An effective Young's modulus was estimated based on experimental force-elongation relationships, and negative Poisson's ratio values were determined from measurements of elongation during stretching. The study demonstrated the feasibility of manufacturing linear auxetic structures using assembly techniques, highlighting their potential for engineering applications.