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Abstract In the presented work, wave dynamics of 2D finite granular crystals of polyurethane cylinders under low-velocity impact loading was investigated to gain better understanding of the influence of lateral constraints. The deformation of the individual grains in the granular crystals during the impact loading was recorded by a high-speed camera and digital image correlation (DIC) was used to calculate high fidelity kinematic and strain fields in each grain. These grain-scale kinematic and strain fields were utilized for the computation of the intergranular forces at each contact using a granular element method (GEM) based mathematical framework. Since the polyurethane were viscoelastic in nature, the viscoelasticity constitutive law was implemented in the GEM framework and it was shown that linear elasticity using the strain rate-dependent coefficient of elasticity is sufficient to use instead of a viscoelastic framework. These particle-scale kinematic and strain field measurements in conjunction with the interparticle forces also provided some interesting insight into the directional dependence of the wave scattering and attenuation in finite granular crystals. The directional nature of the wave propagation resulted in strong wave reflection from the walls. It was also noteworthy that the two reflected waves from the two opposite sidewalls result in destructive interference. These lateral constraints at different depths leads to significant differences in wave attenuation characteristics and the finite granular crystals can be divided into two regions: upper region, with exponential wave decay rate, and lower region, with higher decay rate.
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A class of diatomic 2-D soft granular crystals undergoing pattern transformations
We propose a class of diatomic 2-D soft granular crystals, which features pattern transformation under compression with lateral confinement. The proposed granular crystals are composed of two different types of cylinders: large soft cylinders and small hard cylinders. The pattern-transformable granular crystals are obtained by exploring perturbed packing patterns as potential configurations, and compression with lateral confinement as the driving force of the transition. As a demonstration of the proof-of-concept, we first show the results of desktop-scaled experiments and finite element simulations for a representative case. Then, we present the procedure to obtain these new pattern transformations in soft granular crystals based on the compact packing theory of diatomic circles. The scale-independent compact packing theory serves as an important part of the veiled underlying mechanism of the observed pattern transformations, so the proposed granular crystals can open new avenues in the microstructural design of functional materials towards practical applications.
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- Award ID(s):
- 1649111
- PAR ID:
- 10073785
- Date Published:
- Journal Name:
- Soft Matter
- Volume:
- 13
- Issue:
- 35
- ISSN:
- 1744-683X
- Page Range / eLocation ID:
- 5824 to 5831
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/c7sm01430a
