Condensation of elastic energy in two-dimensional packing of wires.

Forced packing of a long metallic wire injected into a two-dimensional cavity leads to crushed structures involving a hierarchical cascade of loops with varying curvature radii. We study the distribution of elastic energy stored in such systems from experiments, and high-resolution digital techniques. It is found that the set where the elastic energy of curvature is concentrated has dimension D(S) = 1.0 +/- 0.1, while the set where the mass is distributed has dimension D = 1.9 +/- 0.1.