Inside a crumpled ball

Inside a crumpled ballThe crumpling or crushing of paper, aluminum foil, or even a car fender is an everyday occurrence that is surprisingly rich in new physical and materials principles.  Working in the Materials Research Science and Engineering Center (MRSEC) on Polymers at the University of Massachusetts Amherst, Menon and Russell used X-ray microtomography experiments on foils crushed into a ball to understand their detailed 3D structure. These measurements reveal that the internal 3-dimensional geometry of a crumpled ball is in many respects isotropic and homogeneous. Crumpling recapitulates classic nonequilibrium problems such as turbulence, where a system driven by long-wavelength and low-symmetry forces shows only rather subtle fingerprints of the forcing mechanism.  However, the researchers found local nematic ordering of the sheet into parallel stacks, a surprising results that will help physicists and materials scientists better understand these complex structures. The extent of this stacking or layering increased with the volume fraction, or degree of compression.  Stacking of the material into thicker “walls” may be either an alternative or an assistive mechanism to the formation of ridges, and impart structural rigidity to the material.