Sudden ridge collapse in the stress relaxation of thin crumpled polymer films

A crumpled thin sheet generally exhibits numerous defects each of which store energy. When subjected to a constant compressive force the height of the crumple decreases logarithmically with time in. a process of long-term stress relaxation, which scales over several orders of magnitude-i.e., over time periods from seconds to weeks. We have investigated this scaling behavior for thin polymer films and found that a discontinuous stress relaxation is superimposed on the long-term stress relaxation. The former becomes more pronounced as the polymer sheet thickness increases and is systematically characterized in this study. Effects of ridge length and density are discussed.