Composite compression–twist structures made by additive manufacturing for energetic absorption with controllable inner friction

Chiral structures have been recently studied as energy absorbers. The inner friction caused by compression–twisting in chiral structures is inevitable but seldomly studied. Inspired by origami, we propose a combinational structure (including twistable and fixed substructures) to simultaneously generate deformation and friction during compression; one can tune the friction between the two parts by adjusting the distance between the structural center and the balls that constitute the ball-bearing. We made the samples by additive manufacturing. Numerical and experimental studies indicate that the force response and twist angle of the compression–twist structure were affected by four important geometric parameters: initial height, number of polygon sides, strut distribution radius, and design angle. Also, negative stiffness of structure is found. Additionally, one can finely tune the energy absorption effect by the friction between the twist and fixed structure. Our approach is a new research direction for friction energy absorbers; the mechanism of inner friction will be useful in mechanical and aerospace industries.