#force chain

[fuckyeahfluiddynamics]

Seeing Stress in an Avalanche

Researchers sometimes study avalanches and other granular flows in a rolling drum, where grains can cascade down continuously. Here, the twist is that they've done it with photoelastic disks, which show stress patterns when viewed under crossed polarizing filters. (Video and image credit: R. Hodgson et al.)

[fuckyeahfluiddynamics]

Stably Jammed

Granular materials like sand, gravel, and medications can become a rigid mass when squeezed or sheared. Even with a relatively loose packing, these materials can jam together to act like a solid if the contacts between grains no longer allow particles to shift or rotate. (Image and video credit: Y. Zhao et al., research pre-print)

[fuckyeahfluiddynamics]

Fun From the Beach

Here's a neat bit of fluid dynamics derived from a day at the beach! Our experiment begins with well-mixed (and likely compacted) sand grains and sea water in a bottle. Then we flip it! (Video and submission credit: M. Schich; special thanks to Nathalie V. for helpful input) Read the full article

[fuckyeahfluiddynamics]

The Strangeness of Sand

Sand and other granular materials can flow, jam, and transmit forces in counterintuitive ways. This Lutetium Project video gives a nice overview of some of these bizarre properties. (Image and video credit: The Lutetium Project) Read the full article

[fuckyeahfluiddynamics]

The impact of a solid object into a bed of grains is a major topic in many fields from ballistics to astronomy. (Image and research credit: N. Krizou and A. Clark)

[fuckyeahfluiddynamics]

Granular materials like sand and beads can shift and flow in fluid-like ways, but they’re much harder to predict. Part of this is due to the way friction between individual grains transmits force through the network. Here, we see photoelastic beads responding to the intrusion of a narrow rod. The lightning-like flashes show how stress is traveling between neighboring grains. Notice how the lower grains are essentially frozen into a state of high stress, but the movable upper grains shift and readjust themselves to try and relieve stress.

This experiment took place under lunar gravitational conditions. Lower gravity means that it takes a larger pile of grains on top to create a given stress. But it also means it’s easier for those movable top grains to shift or even get thrown up by a hastily applied force.  The purpose of experiments like this is to better understand how rovers and probes should dig in low-gravity environments without kicking up a cloud of regolith and dust. (Image credit: K. Daniels et al., source)

[fuckyeahfluiddynamics]

What goes on inside of a granular material like sand when an object moves through it? Individual grains will shift and may impact one another or simply slide past. Researchers use special photoelastic materials to see these forces in action. A photoelastic material responds to changes in stress by polarizing light, revealing areas of stress concentration. For an entire network of photoelastic beads, forces between the grains appear like a web of lightning. Individual strands are known as force chains. Bright lines indicate areas where grains are jammed against one another in opposition to the object’s movement. As the intruder is pulled against the force chain network, grains shift and new force chains form. (Image credit: Y. Zhang and R. Behringer, source)