Bundling of a twisted thin tube

The twisted end of a candy may at first look simple, but it contains complex features such as the wrinkles and creases that form as the material is packed into a tight bundle. We present experiments where a thin flexible sheet is clamped on two ends and pulled taut, and then twisted to a large angle. We first summarize our recent results showing how the system exhibits an attractive mechanical response in the form of a "tunable locking material." Then we turn to study the deformations at larger twist. While twisting, the shell at first shows an ordered wrinkle pattern that gradually evolves into two cones. At larger twist angles, the material between the cones condenses into a tightly-packed helical structure – a "bundle.". We investigate how this bundle is affected by various geometric and mechanical parameters, such as the aspect ratio of the shell, the normal load, and the geometry of the clamping. Our results show how such tightly-packed structures evolve while twisted and stretched, and how they reflect conditions at larger length scales.