Memory in cyclically crumpled sheets

We investigate the crumpling of an elastoplastic sheet as it is repeatedly crushed onto itself by rolling it into a cylinder and twisting it axially while allowing the end-to-end length to evolve freely. The sheet buckles and folds into structures that repeat but sharpen over hundreds of cycles to a remarkable degree before forming different configurations. Below a critical amplitude, reconfigurations decrease with applied cycles but continue to occur for large enough loading amplitude as the topology of the sheet changes as it tears. The sheet structure as measured by the mean curvature and the total crease length evolves logarithmically with cycle number with a rate that increases with compaction. We explain the progress of creasing using a flat folding model, and we show the logarithmic growth as being a consequence of individual creases becoming sharper with the number of folding cycles, leading to bifurcations in the folding pathway. Published by the American Physical Society 2024