The module offers the possibility to deposit the droplet on a precursor layer, which can be composed of the same or of a different fluid. The vip-drop 2 ex perimental module offers a versatile platform to study a wide range of complex fluids through the deposition of axisymmetric droplets. In particular, microgravity allows to form large droplets while remaining in the regime where surface tension effects and internal driving stresses are predominant over hydrostatic forces. Tweaking the gravitational acceleration under which such droplet is de posited provides access to different regimes, quantified through the Bond number. MaterialsĪxisymmetric droplets provide an ideal demonstration system to study the spreading of complex fluids, which are an essential component of industrial and technological processes, among which additive manufacturing. We propose a combination of microscopic and continuum arguments to rationalize our results. This is coupled with a change in interparticular force balance which takes place under low gravity, as cohesive interactions be come predominant. We interpret these findings as the manifestation of a granular fabric altered by the gravitational force field: in absence of a secondary load (due to gravitational acceleration) to stimulate reorganization in a different direction to the major compression stress, the particles’ configuration becomes stable at lower density, as the particles have no external drive to promote reorganization into a denser packing. The onset of jamming is found to appear at lower packing fraction in microgravity ( φ μ -g J = 0. Results show that piston-probing densifies the packing, eventually leading to jamming of the material compressed by the piston, regardless of the gravitational environment. To query the influence of gravity on powder flow-behavior, a granular material is subjected to compression by a piston in a closed container, on-ground and in microgravity. The macroscopic response of granular solids is determined by the microscopic fabric of force chains, which, in turn, is intimately linked to the history of the solid. These gaps prevent the formation of sealed vacuum cavities between the object and the gripper and in turn hinder the suction mechanism from operating. If the particles used as filling material are too large, the gripper does not conform closely around the object, leaving gaps between the gripper’s membrane and the object. When the gripper is pulled off, mimicking lifting of an object, vacuum pressure is generated in the sealed cavity at the interface gripper–object. Through X-ray computed tomography, we show that small particles (average diameter d = 120 micrometers) achieve higher conformation around the object than larger particles (d = 4mm), thus allowing the formation of air-tight seals. In this work, we experimentally study the effect of particle size on the suction mechanism. Their holding force comes from the combination of three mechanisms: frictional forces, geometrical constraints, and suction effects. Granular grippers are highly adaptable end-effectors that exploit the reversible jamming transition of granular materials to hold and manipulate objects.
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