Emergent yarns and fabrics by twist origami

A first step to making functionalized fabrics is to spin yarns by twisting together a natural or synthetic soft material with a prescribed structure. We will discuss experiments that demonstrate large spontaneous shape transformations that couple with mechanical response starting with a hyperelastic rectangular sheet which is simply held under tension and twisted around its central long axis. For twists larger than half a turn, the sheet adopts an accordion shape with self-contacts and folds oriented at an angle with respect to the axis of rotation. We reconstruct the 3D shape of the folded sheet using x-ray Computed Tomography and calculate the Gaussian and mean curvature to characterize their morphology. Modeling the full soft elastic sheet undergoing such a large transformation is prohibitively difficult. Thus, we propose an origami starting with an inextensible sheet with a prescribed number of triangular folds corresponding those observed at the onset of transverse wrinkling of the elastic sheet as a starting point to analyze the emergence of the structure. Building on this insight, we then present a string model based on the origami kinematics to explain not only the emergence of the accordion folds but also its torsional response.