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Creep and flow of glasses: strain response linked to the spatial distribution of dynamical heterogeneities.

Sentjabrskaja T, Chaudhuri P, Hermes M, Poon WC, Horbach J, Egelhaaf SU, Laurati M - Sci Rep (2015)

Bottom Line: We observe dynamical heterogeneities, namely regions of enhanced mobility, which remain localized in the creep regime, but grow for applied stresses leading to steady flow.These different behaviors are also reflected in the average particle dynamics, quantified by the mean squared displacement of the individual particles, and the fraction of active regions.Both microscopic quantities are found to be proportional to the macroscopic strain, despite the non-equilibrium and non-linear conditions during creep and the transient regime prior to steady flow.

View Article: PubMed Central - PubMed

Affiliation: Condensed Matter Physics Laboratory, Heinrich Heine University, Universitätsstr. 1, 40225 Düsseldorf, Germany.

ABSTRACT
Mechanical properties are of central importance to materials sciences, in particular if they depend on external stimuli. Here we investigate the rheological response of amorphous solids, namely colloidal glasses, to external forces. Using confocal microscopy and computer simulations, we establish a quantitative link between the macroscopic creep response and the microscopic single-particle dynamics. We observe dynamical heterogeneities, namely regions of enhanced mobility, which remain localized in the creep regime, but grow for applied stresses leading to steady flow. These different behaviors are also reflected in the average particle dynamics, quantified by the mean squared displacement of the individual particles, and the fraction of active regions. Both microscopic quantities are found to be proportional to the macroscopic strain, despite the non-equilibrium and non-linear conditions during creep and the transient regime prior to steady flow.

No MeSH data available.


Related in: MedlinePlus

Comparison of (left) experimental and (right) simulation results.(top) Time-dependence of the strain γ(t) for applied stresses σ as indicated, relative to the yield stress σy. (bottom) Mean squared displacement in the vorticity direction, Δy2, (indicated by same colors and line styles), immediately after stress application, i.e. for waiting time tw = 0, and larger tw (as indicated) until the steady-state is reached, i.e. tw→∞ (symbols). For the smaller applied stress, Δy2 is divided by a factor 3 for clarity, both in experiments and simulations.
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f1: Comparison of (left) experimental and (right) simulation results.(top) Time-dependence of the strain γ(t) for applied stresses σ as indicated, relative to the yield stress σy. (bottom) Mean squared displacement in the vorticity direction, Δy2, (indicated by same colors and line styles), immediately after stress application, i.e. for waiting time tw = 0, and larger tw (as indicated) until the steady-state is reached, i.e. tw→∞ (symbols). For the smaller applied stress, Δy2 is divided by a factor 3 for clarity, both in experiments and simulations.

Mentions: If the applied stress σ ≈ σy , a characteristic creep response is observed with the strain increasing sub-linearly with time within the experimental window, γ ~ ta with a ≈ 0.5 (Fig. 1a, broken line). Furthermore, for σ = 0.9σy (Fig. 1b, broken line), a smaller effective exponent is found, in agreement with previous results612282930. Hence, for , the deformation occurs extremely slowly and the system is unable to reach a steady state within the observation time. This is reflected in the particle dynamics in vorticity (neutral) direction, namely the mean squared displacement (MSD) Δy2(t) (Fig. 1c,d, broken lines). In experiments and simulations, at short times the increase of the MSDs is limited, consistent with caging, while at longer times a sub-diffusive regime is observed; Δy2 ~ tb with b < 1. We find b ≈ a within the explored time window. The MSDs show little change with the waiting times tw after the beginning of the stress application (Fig. 1c,d, broken lines). The observed macroscopic creep response and the absence of steady-state flow is thus connected to the particles’ inability to diffuse.


Creep and flow of glasses: strain response linked to the spatial distribution of dynamical heterogeneities.

Sentjabrskaja T, Chaudhuri P, Hermes M, Poon WC, Horbach J, Egelhaaf SU, Laurati M - Sci Rep (2015)

Comparison of (left) experimental and (right) simulation results.(top) Time-dependence of the strain γ(t) for applied stresses σ as indicated, relative to the yield stress σy. (bottom) Mean squared displacement in the vorticity direction, Δy2, (indicated by same colors and line styles), immediately after stress application, i.e. for waiting time tw = 0, and larger tw (as indicated) until the steady-state is reached, i.e. tw→∞ (symbols). For the smaller applied stress, Δy2 is divided by a factor 3 for clarity, both in experiments and simulations.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4495392&req=5

f1: Comparison of (left) experimental and (right) simulation results.(top) Time-dependence of the strain γ(t) for applied stresses σ as indicated, relative to the yield stress σy. (bottom) Mean squared displacement in the vorticity direction, Δy2, (indicated by same colors and line styles), immediately after stress application, i.e. for waiting time tw = 0, and larger tw (as indicated) until the steady-state is reached, i.e. tw→∞ (symbols). For the smaller applied stress, Δy2 is divided by a factor 3 for clarity, both in experiments and simulations.
Mentions: If the applied stress σ ≈ σy , a characteristic creep response is observed with the strain increasing sub-linearly with time within the experimental window, γ ~ ta with a ≈ 0.5 (Fig. 1a, broken line). Furthermore, for σ = 0.9σy (Fig. 1b, broken line), a smaller effective exponent is found, in agreement with previous results612282930. Hence, for , the deformation occurs extremely slowly and the system is unable to reach a steady state within the observation time. This is reflected in the particle dynamics in vorticity (neutral) direction, namely the mean squared displacement (MSD) Δy2(t) (Fig. 1c,d, broken lines). In experiments and simulations, at short times the increase of the MSDs is limited, consistent with caging, while at longer times a sub-diffusive regime is observed; Δy2 ~ tb with b < 1. We find b ≈ a within the explored time window. The MSDs show little change with the waiting times tw after the beginning of the stress application (Fig. 1c,d, broken lines). The observed macroscopic creep response and the absence of steady-state flow is thus connected to the particles’ inability to diffuse.

Bottom Line: We observe dynamical heterogeneities, namely regions of enhanced mobility, which remain localized in the creep regime, but grow for applied stresses leading to steady flow.These different behaviors are also reflected in the average particle dynamics, quantified by the mean squared displacement of the individual particles, and the fraction of active regions.Both microscopic quantities are found to be proportional to the macroscopic strain, despite the non-equilibrium and non-linear conditions during creep and the transient regime prior to steady flow.

View Article: PubMed Central - PubMed

Affiliation: Condensed Matter Physics Laboratory, Heinrich Heine University, Universitätsstr. 1, 40225 Düsseldorf, Germany.

ABSTRACT
Mechanical properties are of central importance to materials sciences, in particular if they depend on external stimuli. Here we investigate the rheological response of amorphous solids, namely colloidal glasses, to external forces. Using confocal microscopy and computer simulations, we establish a quantitative link between the macroscopic creep response and the microscopic single-particle dynamics. We observe dynamical heterogeneities, namely regions of enhanced mobility, which remain localized in the creep regime, but grow for applied stresses leading to steady flow. These different behaviors are also reflected in the average particle dynamics, quantified by the mean squared displacement of the individual particles, and the fraction of active regions. Both microscopic quantities are found to be proportional to the macroscopic strain, despite the non-equilibrium and non-linear conditions during creep and the transient regime prior to steady flow.

No MeSH data available.


Related in: MedlinePlus