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The transient dynamics of dilation waves in granular phase transitions during silo discharge


Granular material has the unique ability to transition between solid and liquid-like phases, but quantitative observations of the dynamics involved in this process remain rare. We hypothesize that granular packing of the solid phase has a leading control on this transition. To test this, we visualize the flow transitions that occur during discharge from a grain-filled silo. X-ray fluoroscopy and high-speed video analysis are used to detect and characterize the kinematics of dilation waves that trigger the phase transitions. Wave velocities are shown to vary by an order of magnitude with strong dependence on the packing density of the initially static bed. The speed of dilation waves exceeds any granular flow velocity in the system, and a simple model based upon conservation of mass is presented to describe this phenomenon. Our results have major implications for the quantitative description and prediction of granular system behaviour in natural and industrial applications, particularly with regards to the onset of avalanche motion and the handling of powders and grains.

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The authors would like to acknowledge the Massey University Research Fund (MURF) for funding. We also thank Bronwen Comrie-Evans and John Edwards for the use of laboratory space, and Diane Orange for helpful discussions and access to the X-ray facilities. Finally, we thank the reviewers of this manuscript for their excellent suggestions for improvement during the first review of the manuscript.

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Correspondence to L. A. Fullard.

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The authors acknowledge the Massey University research fund for providing funding for this project. The authors have no conflicts of interest to declare.

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Fullard, L.A., Davies, C.E., Lube, G. et al. The transient dynamics of dilation waves in granular phase transitions during silo discharge. Granular Matter 19, 6 (2017).

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  • Granular material
  • Silo
  • Dilation