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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

(a) Box-box correlation functions G(r) for stress σ/σy ≈ 5 and time , 0.20, 0.27, 0.43, 0.53, 0.66, 0.80 and 0.93 (left to right) as observed in experiments. Lines represent stretched exponential fits. (b) Correlation length of active boxes, ξ, as a function of time for σ/σy ≈ 5.0; the line indicates ξ/dL ~ t2/3.
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f6: (a) Box-box correlation functions G(r) for stress σ/σy ≈ 5 and time , 0.20, 0.27, 0.43, 0.53, 0.66, 0.80 and 0.93 (left to right) as observed in experiments. Lines represent stretched exponential fits. (b) Correlation length of active boxes, ξ, as a function of time for σ/σy ≈ 5.0; the line indicates ξ/dL ~ t2/3.

Mentions: The larger area in the velocity-vorticity plane monitored in the experiments allows us to quantitatively investigate the spatial growth of active regions. If the box lm is active or inactive, nlm is defined as 1 or 0, respectively. Based on this definition, we calculate the spatial correlation of active boxes, that is the box-box correlation function, with r2 = (l–l′)2 + (m–m′)2 (Fig. 6a). The brackets indicate an average over the individual boxes. The characteristic length ξ of the spatial correlation G(r) was determined by fitting a stretched exponential function to G(r). The correlation length ξ(t) increases from an initial value ξ ≈ 5dL at to ξ ≈ 30dL at , with ξ(t) ~ t2/3 (Fig. 6b). For σ ≈ σy the correlation length ξ(t) instead does not grow and stays approximately constant for all times t (data not shown).


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)

(a) Box-box correlation functions G(r) for stress σ/σy ≈ 5 and time , 0.20, 0.27, 0.43, 0.53, 0.66, 0.80 and 0.93 (left to right) as observed in experiments. Lines represent stretched exponential fits. (b) Correlation length of active boxes, ξ, as a function of time for σ/σy ≈ 5.0; the line indicates ξ/dL ~ t2/3.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f6: (a) Box-box correlation functions G(r) for stress σ/σy ≈ 5 and time , 0.20, 0.27, 0.43, 0.53, 0.66, 0.80 and 0.93 (left to right) as observed in experiments. Lines represent stretched exponential fits. (b) Correlation length of active boxes, ξ, as a function of time for σ/σy ≈ 5.0; the line indicates ξ/dL ~ t2/3.
Mentions: The larger area in the velocity-vorticity plane monitored in the experiments allows us to quantitatively investigate the spatial growth of active regions. If the box lm is active or inactive, nlm is defined as 1 or 0, respectively. Based on this definition, we calculate the spatial correlation of active boxes, that is the box-box correlation function, with r2 = (l–l′)2 + (m–m′)2 (Fig. 6a). The brackets indicate an average over the individual boxes. The characteristic length ξ of the spatial correlation G(r) was determined by fitting a stretched exponential function to G(r). The correlation length ξ(t) increases from an initial value ξ ≈ 5dL at to ξ ≈ 30dL at , with ξ(t) ~ t2/3 (Fig. 6b). For σ ≈ σy the correlation length ξ(t) instead does not grow and stays approximately constant for all times t (data not shown).

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