Self-folded pleated structures in twisted elastic sheets*

We examine with experiments the post-wrinkling growth of curvature condensation and self-folded structures in thin sheets which are twisted about their axis while held under tension. Using x-ray imaging, we show that the initial sinusoidal wrinkles are found to increasing focus curvature resulting in spontaneous development of pleated structures. Unlike purely tensional wrinkles which decrease in amplitude after an application of a critical strain, the wrinkles are observed to persist and approach a finite value given by the mode number of the primary instability. The number of pleats can be controlled by varying the applied tension and the aspect ratio of the sheet with greater width to length ratios giving rise to more wrinkles and pleats.