Stress Focusing in Thin Curved Films

Origami design requires a sheet to be bent several times, often with bends meeting at an angle. Interestingly, the vertex of two bends causes stress focusing in the form of conical structures which are known as developable cones or d-cones. In our experiments, we report the formation of d-cones far from a set of curved, fixed boundaries. This is unique compared to earlier experiments in which d-cones were physically realized though free-boundary contact geometries which involved point contact at or near the site of the asymptotically-singular structure. We experimentally study how the onset of singular behavior resulting from applied strain depends on the thickness, size, and material of the film. Along with the onset of singularities in the films, we discuss general mechanical properties and morphologies observed in experiments, and speculative on the relationships identified in our data.