Abstract
We observe nonmonotonic aging and memory effects, two hallmarks of glassy dynamics, in two disordered mechanical systems: crumpled thin sheets and elastic foams. Under fixed compression, both systems exhibit monotonic nonexponential relaxation. However, when after a certain waiting time the compression is partially reduced, both systems exhibit a nonmonotonic response: the normal force first increases over many minutes or even hours until reaching a peak value, and only then is relaxation resumed. The peak time scales linearly with the waiting time, indicating that these systems retain long-lasting memory of previous conditions. Our results and the measured scaling relations are in good agreement with a theoretical model recently used to describe observations of monotonic aging in several glassy systems, suggesting that the nonmonotonic behavior may be generic and that athermal systems can show genuine glassy behavior.
Highlights
We observe non-monotonic aging and memory effects, two hallmarks of glassy dynamics, in two disordered mechanical systems: crumpled thin sheets and elastic foams
In this Letter, we report non-monotonic aging dynamics that give rise to a maximum in the relaxation curve
When the compression is decreased after a certain waiting time, the stress evolution remarkably becomes non-monotonic: under constant compression, the measured normal force first increases slowly over seconds to hours, reaches a well-defined peak, and reverses to a renewed slow relaxation (Fig. 1c,f)
Summary
We observe non-monotonic aging and memory effects, two hallmarks of glassy dynamics, in two disordered mechanical systems: crumpled thin sheets and elastic foams. Both systems exhibit monotonic, slow stress relaxation (Fig. 1b,e).
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