Abstract
Athermal systems across a large range of length scales, ranging from foams and granular bead
packings to crumpled metallic sheets, exhibit slow stress relaxation when compressed. Experi-
mentally they show a non-monotonic stress response when decompressed somewhat after an initial
compression, i.e. under a two-step, Kovacs-like protocol. It turns out that from this response one
can tell for how long the system was in a compressed state, suggesting an interpretation as a memory
effect. In this work we use a model of an athermal jammed solid, specifically a binary mixture of
soft harmonic particles, to explore this phenomenon through in-silico experiments. Using extensive
simulations under conditions analogous to those in experiment, we observe identical phenomenology
in the stress response under a two–step protocol. Our model system also recovers the behaviour
under a more recently studied three–step protocol, which consists of a compression followed by a
decompression and then a final compression. We show that the observed response in both two–step
and three–step protocols can be understood using Linear Response Theory. In particular, a linear
scaling with age for the two-step protocol arises generically for slow linear responses with power law
or logarithmic decay and does not in itself point to any underlying aging dynamics
packings to crumpled metallic sheets, exhibit slow stress relaxation when compressed. Experi-
mentally they show a non-monotonic stress response when decompressed somewhat after an initial
compression, i.e. under a two-step, Kovacs-like protocol. It turns out that from this response one
can tell for how long the system was in a compressed state, suggesting an interpretation as a memory
effect. In this work we use a model of an athermal jammed solid, specifically a binary mixture of
soft harmonic particles, to explore this phenomenon through in-silico experiments. Using extensive
simulations under conditions analogous to those in experiment, we observe identical phenomenology
in the stress response under a two–step protocol. Our model system also recovers the behaviour
under a more recently studied three–step protocol, which consists of a compression followed by a
decompression and then a final compression. We show that the observed response in both two–step
and three–step protocols can be understood using Linear Response Theory. In particular, a linear
scaling with age for the two-step protocol arises generically for slow linear responses with power law
or logarithmic decay and does not in itself point to any underlying aging dynamics
| Original language | English |
|---|---|
| Journal | Physical Review Research |
| Publication status | Accepted/In press - 17 Nov 2021 |