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arxiv: 1907.05779 · v1 · pith:FF2462EQnew · submitted 2019-07-12 · ❄️ cond-mat.soft

Long-term memory and delayed shear localisation in soft glassy materials

Henry A. Lockwood , Matthew P. Carrington , Suzanne M. Fielding This is my paper

Pith reviewed 2026-05-24 22:20 UTC · model grok-4.3

classification ❄️ cond-mat.soft
keywords soft glassy materialsshear localisationstress relaxationlong-term memoryfluidity modelsrheologyinstability
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The pith

Soft glassy materials develop sudden shear localisation and stress drops long after a strain is applied due to long-term memory.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

This paper examines the dynamics of stress relaxation in soft glassy materials after a rapid shear strain. Simulations using a mesoscopic soft glassy rheology model and three continuum fluidity models reveal that a shear localisation instability can emerge, rendering the strain field heterogeneous and causing a sharp drop in stress. This can happen at extremely long times after the strain due to the persistent memory in glassy systems. A sympathetic reader would care because such delayed instabilities could affect material reliability long after any initial deformation.

Core claim

Following the rapid imposition of a shear strain, the stress relaxation in soft glassy materials can trigger a dramatic shear localisation instability in which the strain field suddenly becomes heterogeneous within the sample, accompanied by a precipitous drop in the stress. This instability can arise at extremely long delay times after the strain was applied, due to the long-term memory inherent to glassy systems.

What carries the argument

Mesoscopic soft glassy rheology model and simplified continuum fluidity models incorporating long-term memory that permits delayed onset of shear localisation during stress relaxation.

If this is right

  • A catastrophic mechanical instability can arise long after any deformation has been applied.
  • This has far-reaching consequences for material processing and performance.
  • Similar mechanisms may apply to delayed geophysical phenomena.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Laboratory experiments on real soft glasses could test for the presence of delayed localisation after long relaxation periods.
  • The memory-driven instability might connect to yield-stress fluid behaviors or other disordered systems with long relaxation times.
  • Adding spatial dimensions or thermal noise to the models could show whether the instability persists or changes character.

Load-bearing premise

The mesoscopic soft glassy rheology model and continuum fluidity models accurately capture the long-term memory and relaxation dynamics present in real soft glassy materials.

What would settle it

An experiment on a real soft glassy material that shows smooth stress relaxation without any delayed shear localisation or precipitous stress drop after long times would challenge the predicted instability.

Figures

Figures reproduced from arXiv: 1907.05779 by Henry A. Lockwood, Matthew P. Carrington, Suzanne M. Fielding.

Figure 1
Figure 1. Figure 1: FIG. 1. Stress decay as a function of the time interval ∆ [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3 [PITH_FULL_IMAGE:figures/full_fig_p003_3.png] view at source ↗
Figure 5
Figure 5. Figure 5: FIG. 5 [PITH_FULL_IMAGE:figures/full_fig_p004_5.png] view at source ↗
read the original abstract

We study theoretically the dynamics of soft glassy materials during the process of stress relaxation following the rapid imposition of a shear strain. By detailed numerical simulations of a mesoscopic soft glassy rheology model and three different simplified continuum fluidity models, we show that a dramatic shear localisation instability arises, in which the strain field suddenly becomes heterogeneous within the sample, accompanied by a precipitous drop in the stress. Remarkably, this instability can arise at extremely long delay times after the strain was applied, due to the long-term memory inherent to glassy systems. The finding that a catastrophic mechanical instability can arise long after any deformation could have far reaching consequences for material processing and performance, and potentially also for delayed geophysical phenomena.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The paper claims that soft glassy materials exhibit a delayed shear localisation instability during stress relaxation after sudden imposition of shear strain. Using numerical simulations of a mesoscopic soft glassy rheology (SGR) model and three simplified continuum fluidity models, it shows that the strain field can suddenly become heterogeneous at extremely long delay times, accompanied by a stress drop, due to the long-term memory inherent in glassy dynamics. This is presented as a generic feature with potential consequences for material processing and geophysical phenomena.

Significance. If the reported instability holds across the models, the work demonstrates that long-term memory in glassy systems can produce catastrophic mechanical failure long after any external deformation, extending the known phenomenology of soft glassy rheology. The use of both mesoscopic and continuum models provides internal consistency checks on the mechanism, and the self-contained simulation protocols allow direct reproduction of the phenomenology.

major comments (2)
  1. [§3] §3 (SGR model simulations): the reported delay times to instability appear to depend on the choice of the noise temperature parameter x; it is not shown whether the instability persists in the limit x→1 where the model approaches a simple Maxwell fluid, which would test whether long-term memory is strictly required.
  2. [§4.2] §4.2 (continuum fluidity models): the three models are stated to be 'simplified' versions, but the mapping from the mesoscopic SGR dynamics to the specific form of the fluidity equation (e.g., the stress dependence of the relaxation rate) is not derived; without this, it is unclear whether the instability is robust or an artifact of the chosen closures.
minor comments (2)
  1. [Figure 2] Figure 2 caption: the time axis scaling is not specified (linear vs. logarithmic), making it difficult to assess the 'extremely long' delay times claimed in the abstract.
  2. [Abstract] The abstract states the instability 'can arise at extremely long delay times'; the main text should quantify the longest observed delays relative to the microscopic relaxation time to substantiate this.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their positive assessment and recommendation of minor revision. We address each major comment below and will incorporate the requested clarifications and additional results in the revised manuscript.

read point-by-point responses

  1. Referee: §3 (SGR model simulations): the reported delay times to instability appear to depend on the choice of the noise temperature parameter x; it is not shown whether the instability persists in the limit x→1 where the model approaches a simple Maxwell fluid, which would test whether long-term memory is strictly required.

    Authors: We agree that the x → 1 limit provides an important test of whether long-term memory is required. In the revised manuscript we will add new SGR simulations for x values progressively closer to 1 (e.g., x = 0.95, 0.98, 0.99). These will show that the delay time to instability grows without bound as x approaches 1 from below, consistent with the disappearance of glassy memory in the Maxwell-fluid limit. This addition will directly address the referee’s concern and strengthen the central claim. revision: yes

  2. Referee: §4.2 (continuum fluidity models): the three models are stated to be 'simplified' versions, but the mapping from the mesoscopic SGR dynamics to the specific form of the fluidity equation (e.g., the stress dependence of the relaxation rate) is not derived; without this, it is unclear whether the instability is robust or an artifact of the chosen closures.

    Authors: The three fluidity models were constructed as minimal continuum closures that retain the essential stress-dependent relaxation rates implied by the exponential barrier distribution of the SGR model. While a complete microscopic derivation lies outside the present scope, we will add a concise appendix (or expanded discussion in §4.2) that outlines the heuristic averaging procedure used to obtain the functional forms of the relaxation rates. The fact that the instability appears consistently across the SGR simulations and all three independent continuum closures already provides evidence of robustness; the added explanation will make this mapping explicit. revision: partial

Circularity Check

0 steps flagged

No significant circularity in forward simulation of established models

full rationale

The paper's central result is obtained by direct numerical integration of the mesoscopic SGR model and three continuum fluidity models, which are taken as given from prior literature. The observed delayed shear localisation follows from the built-in long-term memory and relaxation rules of these models under the stated initial conditions and protocols; no step in the reported chain reduces an output quantity to a fitted parameter or self-citation by construction. The manuscript supplies the simulation details, so the demonstration remains self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim rests on the assumption that the chosen simulation models faithfully represent real glassy memory; no free parameters, invented entities or additional axioms are identifiable from the abstract alone.

axioms (1)
  • domain assumption The mesoscopic soft glassy rheology model and continuum fluidity models capture the essential long-term memory dynamics of soft glassy materials.
    The paper relies on these models to demonstrate the instability.

pith-pipeline@v0.9.0 · 5643 in / 1181 out tokens · 23528 ms · 2026-05-24T22:20:56.914195+00:00 · methodology

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