Structural response of thin folded membranes

There has been an recent upsurge of interest in the geometrical reconfiguration of thin sheets by an engineered pattern of folds that enables foldability. Examples range from origami-based metamaterials to self-assembly of polymer sheets and solar sails. In addition to this designed folding pattern, additional creases often appear as an unintended by-product of the folding process, particularly in cases when the pattern is not rigid-foldable. Although often modeled as perfect line hinges, folds and creases have a non-zero bending stiffness around a neutral folding angle, which significantly alter the mechanical response of the sheet. Design and prediction of the behavior of such structures require a careful characterization of the crease behavior. We perform experiments on sheets with a wide range of geometric and material properties, to rationalize the mechanical properties of folds as a function of the folding process and applied loading. We found that the results fundamentally depend on the microstructure of the sheet and the loading history. The results of this model experiments will then be used in the analysis of complicated folding patterns.