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Studying Large Amplitude Oscillatory Shear Response of Soft Materials
Published on: April 25, 2019
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Local structure controls the nonaffine shear and bulk moduli of disordered solids
M Schlegel1, J Brujic2, E M Terentjev3
1University of Cambridge, Department of Engineering, Trumpington Street Cambridge CB2 1PZ, UK.
Scientific Reports
|January 7, 2016
Summary
This study connects microscopic structure to macroscopic elasticity in amorphous solids. It explains why packings are stiffer under compression than shear, offering a new theory for elasticity in materials like emulsions.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Statistical Mechanics
Background:
- Understanding the relationship between microscopic structure and macroscopic elasticity in amorphous solids is a fundamental challenge.
- Existing models (e.g., random networks, sphere packings) exhibit different elastic moduli (shear G, compression K) due to varying particle arrangements and correlations.
- A microscopic explanation for the observed differences in G and K, and their ratio, has been lacking.
Purpose of the Study:
- To establish a quantitative analytical connection between local orientational order and elasticity in model amorphous solids.
- To investigate the influence of microstructure on the mechanical response, specifically comparing dense packings and sparse networks.
- To provide a microscopic explanation for the observed ratio of shear to compression moduli (G/K) in amorphous materials.
Main Methods:
- Development of a theoretical framework connecting local orientational order to macroscopic elastic moduli.
- Analysis of two limiting cases: dense sphere packings (strong excluded-volume effects) and idealized networks (no excluded-volume).
- Comparison of theoretical predictions with experimental data for compressed emulsions.
Main Results:
- The theory quantitatively links local orientational order to elasticity in amorphous solids with varying microstructures.
- In packings, excluded-volume interactions lead to less non-affinity (greater stiffness) under compression compared to shear.
- This microstructural effect explains the lower G/K values observed in packings, a phenomenon previously lacking a microscopic basis.
- The theory accurately describes the elasticity of compressed emulsions across a range of packing fractions using a single parameter.
Conclusions:
- Local orientational order significantly influences the macroscopic elastic response of amorphous solids.
- The developed theory provides a unified explanation for the elasticity of different amorphous materials, from networks to packings.
- This work offers a microscopic understanding of the G/K ratio and its dependence on material microstructure, validated by experimental data.
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