2026/02/17 by Tom Marzin, Barath Venkateswaran, Yuchen Xi +2 · 3 voices
Physics and Astronomy · #cond-mat.soft
Like a crêpe resting on a plate, a thin elastic sheet can fold smoothly under its own weight, forming reversible shapes without creases or imposed hinges. Such soft folds arise from a balance between elastic bending and gravity, yet their stability, packing limits, and dynamics remain poorly understood. Here we show that these behaviors are governed by a single physical length scale, the elasto-gravity length ℓeg. Using experiments and heavy-elastica theory, we demonstrate that ℓeg sets the characteristic fold geometry, determines when a fold becomes unstable and unfolds, and limits how many reversible folds can be stacked in rectangular and circular sheets. In particular, when lengths are rescaled by ℓeg, fold shapes and stability thresholds collapse across materials and thicknesses. We further show that unfolding follows a universal speed scaling v ∼ √g ℓeg, revealing a gravity-controlled time scale for the release of stored bending energy. Together, these results establish a unified physical framework for reversible folding, compact storage, and gravity-assisted deployment of thin elastic sheets.