Extension twist deformation response of an auxetic cylindrical structure inspired by deformed cell ligaments

Recent advances in artificial metamaterials have allowed unique structures to deform in distinct modes not previously found in traditional material form. Auxetic structures that induce twist through deformation have been a focus of recent research. In this paper a cell-based tubular structure with pre-deformed ligaments is proposed which exhibits efficient extension induced twist (EIT) without the limitations of buckling. An analytical model of the structure is proposed using cell parameters to characterize the non-linear twist-deformation relationship. Samples of the structure were fabricated using the Ultimaker 3 platform with elastomer based TPU 95a build material and PVA support material. The analytical model and FEM were validated by tensile experiments, where fabricated samples reached 60 degrees of non-linear axial twist over 40 mm of deformation. In order to further characterize the structure's twist response, key design parameters of the lattice structure were varied and modelled. Actuation through tensile elastic deformation has key advantages in reliability and reduced complexity. Due to these advantages, this technology has potential applications in aerospace, biomedical and robotic fields.