Ideal states of granular matter in space

author: Matthias Sperl, German Aerospace Center (DLR)
published: April 23, 2019,   recorded: April 2019,   views: 131


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Second only to water in volume, granular matter is the most frequently used material or material state in industry. Despite its importance in engineering, many physical foundations of granular matter are only now being investigated. A major obstacle to describe granular matter within statistical physics is the strong influence of out-of-equilibrium dynamics: Already the two-particle collision breaks time-reversal symmetry due to energy loss and renders granular systems out-of-equilibrium and thus a challenge in theory and experiment alike. In addition, granular matter at different densities is strongly susceptible to the influence of gravity. Hence, experiments require and can benefit from experiments in microgravity: On ground, granular gases sediment quickly, agitated granular fluids are strongly anisotropic, and granular packings exhibit large gradients in pressure. For all three of those states, experiments on several platforms such as parabolic flight, drop tower, sounding rocket and International Space Station demonstrate access to unique and ideal ensembles under microgravity. Granular gases can be agitated homogeneously, granular fluids observed under isotropic conditions, and granular solids monitored free of gradients. In order to characterize those ideal states a variety of diagnostics can be applied: video imaging, light-scattering, X-ray radiography, stress birefringence, and sound transmission. A synopsis shall be given how the results from these experiments provide valuable insights into the behavior of granular matter and contribute to a deeper understanding

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