  Thin elastic solids are easily deformed into a myriad of three-dimensional
shapes, which may contain sharp localized structures as in a crumpled candy
wrapper, or have smooth and diffuse features like the undulating edge of a
flower. Anticipating and controlling these morphologies is crucial to a variety
of applications involving textiles, synthetic skins, and inflatable structures.
Here we show that a "wrinkle-to-crumple" transition, previously observed in
specific settings, is a ubiquitous response for confined sheets. This unified
picture is borne out of a suite of model experiments on polymer films confined
to liquid interfaces with spherical, hyperbolic, and cylindrical geometries,
which are complemented by experiments on macroscopic membranes inflated with
gas. We use measurements across this wide range of geometries, boundary
conditions, and lengthscales to quantify several robust morphological features
of the crumpled phase, and we build an empirical phase diagram for crumple
formation that disentangles the competing effects of curvature and compression.
Our results suggest that crumples are a generic microstructure that emerge at
large curvatures due to a competition of elastic and substrate energies.
