Memory formation in cyclically deformed amorphous solids and sphere assemblies

Abstract

We study a model amorphous solid that is subjected to repeated athermal cyclic shear deformation. It has previously been demonstrated that the memory of the amplitudes of shear deformation the system is subjected to (or trained at) is encoded, and can be retrieved by subsequent deformation cycles that serve as read operations. Here we consider different read protocols and measurements and show that single and multiple memories can be robustly retrieved through these different protocols. We also show that shear deformation by a larger amplitude always erases the stored memories. These observations are similar to those in experiments with non-Brownian colloidal suspensions and corresponding models, but differ in the possibility of storing multiple memories non-transiently. Such a possibility has been associated with the presence of cycles of transitions that take place in the model amorphous solids, between local energy minima. Here, we also study low-density sphere assemblies which serve as models for non-Brownian colloidal suspensions, under athermal deformation, and identify a regime where the signatures of memory encoding are similar to the model glass, even when transition between local energy minima are absent. We show that such a regime corresponds to the presence of loop reversibility, rather than point reversibility of configurations under cyclic deformation.

Global memory from local hysteresis in an amorphous solid

“…Consistent with other studies [7,[16][17][18], we see evidence for both single and multiple memories. When we train with both 3% and 4% strain, applying γ 1 = 3% last before readout ( Fig.…”

“…In this paper, we describe experiments with the twodimensional amorphous solid in Fig. 1a, showing the readout of stored memories, consistent with other systems [7,[16][17][18]. We propose that these memory results are approximately consistent with a behavior called return-point memory (RPM) that is exhibited by many hysteretic systems [6,20,21].…”

“…A local minimum in the MSD as a function of γ read shows evidence of the training amplitude, as in Figs. 1c (our experiments) and d (simulations of Adhikari et al [17]). If the same pro-cedure is performed with a dilute non-Brownian suspension, the data reveal the training amplitude in a different way: the MSD is negligible until γ read exceeds the training amplitude (inset of Fig.…”

“…Error bars represent standard deviation of mean for several trials[19]. (d) Analogous readout of 6% training in simulations of an amorphous solid, adapted from Adhikari et al[17]. Inset: Analogous readout in dilute suspension experiments by Paulsen et al[3].…”

Embedding orthogonal memories in a colloidal gel through oscillatory shear

“…Further studies have argued that this oscillatory shear memory effect should apply to disordered systems in generalshearing causes rearrangement which continues until a reversible state is found [6][7][8]. Indeed, similar memory effects have been found in experiments and simulations of model amorphous systems [2,9,10], granular systems [11], and glasses [12][13][14][15]. The interactions between particles can vary and even the nature of the reversibility can vary for different systems [9,[16][17][18][19][20].…”