Science

The SPACE GRAINS project is devoted to study the dynamical and statistical properties of granular materials in low-gravity environment, from dilute to dense regimes. Space Grains team gathers scientists from 17 groups over 8 countries.

 

In order to reach scientific objectives, an instrument, called VIP-GRAN (Vibration Induced Phenomena in Granular Materials), is currently developed by the European Space Agency (ESA) and DTM s.r.l., and will be included in the European Drawner Rack (EDR) onboard International Space Station (ISS) in 2021. Parabolic flight version of the instrument is exploited since 2015.

The instrument consists of a 3D close cell containing particles, two opposite walls of the cell being vibrating pistons. Control parameters are the number of particles, the geometry of the container, and the amplitude and the frequency of vibrations. Cameras, accelerometers, and impact force sensors are implemented. Different cells are used, and are interchangeable on the instrument : 2D cell, 3D cells, shear cell, acoustic cell, …

Motivation for low gravity. Dilute regimes of granular media (e.g. liquid- or gas-like phases) are extremely sensitive to any symmetry breaking effect due to gravity such as sedimentation. For dense regimes, confinement pressure of grains due to their own weight modifies deeply their rheology, and acoustic properties. Moreover, some phenomena under scrutiny (e.g. convection, cooling, segregation and jamming) need long duration experiments and high level of low-gravity to avoid g-jitters.

Typical experiments with the instrument concern the study of phase transitions occurring in a granular matter between a liquid-like phase and a gas-like one when submitted to mechanical vibrations. One aim is to test the limit of validity of kinetic theory of granular gases when the solid fraction is changed from a dilute regime to a dense one. Indeed, theoretical works try to extend  the validity range the hydrodynamic limit of kinetic theory to dense system (see WP1). Another set of experiments (WP3) will concern the study of global granular motions induced by convection when both pistons vibrate differently («thermal gradient»-like forcing). Although studied on ground with one or two different species (segregation by convection, rotating drums), no convection-like behaviors with one species has been observed in wheightlessness to our knowledge. Third, experiments devoted to dense granular system will be also performed to better understand mechanical stresses and sound propagation (WP2). Finally, the effect of aspherical particles or different species will be also investigated (WP4). The proposed experiments are selected within Work Packages.