Non-Monotonic Aging and Memory Retention in Disordered Mechanical Systems

School of Engineering and Applied Sciences, Harvard University

From materials such as polymers and glass to properties of interfaces leading to friction and even earthquakes, many disordered systems exhibit a similar repertoire of far-from-equilibrium behavior such as non-exponential relaxations, aging and memory effects. Yet, in spite of numerous studies of these recurring motifs, identifying the mechanisms underlying the unusual out-of-equilibrium dynamics of disordered systems remains a challenge.

I will describe the experimental observation of slow relaxation, aging and memory effects - hallmarks of glassy dynamics - in two disordered mechanical systems: crumpled thin sheets and elastic foams. In particular, I'll report the observation of a non-monotonic aging response that can last many hours. I will then describe ongoing experiments that exploit the macroscopic nature of these systems to characterize the underlying mechanisms. The experimental results are in good agreement with a theoretical model recently used to describe observations of monotonic aging in several glassy systems. This suggests not only a general mechanism, but also that the non-monotonic behavior we observe may be generic and that a-thermal systems can show genuine glassy behavior.