Summary: Relaxation mechanisms in the unfolding of thin sheets
and M. Adda-Bedia2
Laboratoire de Physique et M´ecanique des Milieux H´et´erog`enes, CNRS-ESPCI-UPMC Paris 6,
Universit´e Paris Diderot, 10 rue Vauquelin, 75005 Paris, France.
Laboratoire de Physique Statistique, Ecole Normale Sup´erieure, UPMC Paris 6,
Universit´e Paris-Diderot, CNRS, 24 rue Lhomond, 75005 Paris, France.
(Dated: March 10, 2011)
When a thin sheet is crumpled, creases form in which plastic deformations are localized. Here we
study experimentally the relaxation process of a single fold in a thin sheet subjected to an external
strain. The unfolding process is described by a quick opening at first, and then a progressive slow
relaxation of the crease. In the latter regime, the necessary force needed to open the folded sheet at
a given displacement is found to decrease logarithmically in time, allowing its description through
an Arrhenius activation process. We accurately determine the parameters of this law and show its
general character by performing experiments on both Mylar and paper sheets.
PACS numbers: 62.40.+i, 46.35.+z, 68.55.-a, 46.32.+x, 64.70.qd.
The physics of folding display interesting phenomena
in connection with mechanical and geometrical prop-