Morphological phases of crumpled wire

The loops and folds that result when a sheet, tape, or wire crumples are of practical and theoretical interest. Engineers want to predict how structures deform under stress; physicists want to reduce diverse crumpling behavior to a few simple principles. Toward that second aim, Norbert Stoop, Falk Wittel, and Hans Herrmann of ETH Zürich have conducted an experimental study of one elementary system: a length of metal wire stuffed from two opposing directions into a cylindrical container so shallow that the crumpling is two-dimensional. At the start of each run, the wire spanned the container in a straight line. Two counterrotating drums then pushed more and more of the wire into the container until, having bent to form a loop, the wire touched the side. What happened next, the researchers found, depended on the wire’s elasticity and on the friction between the wire and the container. When friction is high,...