Aging and Memory Effects in Disordered and Frustrated Mechanical Systems

I will discuss the observation of some of the hallmarks of glassy dynamics - slow relaxation, aging and memory effects - in a-thermal, macroscopically-disordered mechanical systems: ultra-thin crumpled sheets, elastic foams and granular systems. I’ll focus on the observation of an extremely long-lasting non-monotonic memory response, reminiscent of the Kovacs effect observed decades ago in glassy polymer melts and metallic glasses. I will describe ongoing experiments that aim to exploit the macroscopic nature of the our systems to try and uncover the mechanisms underlying the slow relaxation and memory retention exhibited by them. The experimental results, down to surprisingly subtle details, are in very good agreement with a phenomenological framework which has recently been used to explain monotonic aging effects in several glassy systems. This suggests not only a general mechanism for slow relaxation and memory retention, but also that the non-monotonic behavior we observe may be generic.