Pick up a handful of sand, and it flows through your fingers like a liquid. But when you walk on the beach, the sand supports your weight like a solid. What happens to the forces between the jumbled sand grains when you step on them to keep you from sinking?
An international team of researchers collaborating at Duke University have developed a new way to measure the forces inside materials such as sand, soil or snow under pressure.
Physicists are using this computerized 3-D rendering of beads in a box to serve as a model for soil, sand or snow. Colored lines show the network of forces as the virtual particles are pushed together. Thick red lines connect the particles that are experiencing the brunt of the force. By studying the forces inside granular materials as they're pressed, pushed or squeezed, the researchers hope to better understand phenomena like the jamming of grain hoppers or the early warning signs of earthquakes and avalanches.
Credit: Video courtesy of Nicolas Brodu.
Described in the March 5 issue of Nature Communications, the technique uses lasers coupled with force sensors, digital cameras and advanced computer algorithms to peer inside and measure the forces between neighboring particles in 3-D.
The new approach will allow researchers to better understand phenomena like the jamming of grain hoppers or the early warning signs of earthquakes and avalanches, said study co-author Nicolas Brodu, now at the French institute Inria.
Whether footprints in sand, or the force of gravity on a mountain slope, physicists have long sought to understand what happens inside granular materials as they're pressed, pushed or squeezed.
For centuries this simple question has been surprisingly difficult to answer. But more recently, thanks to advances in 3-D imaging techniques and the number-crunching power of computers, researchers are starting to get a better picture of what happens when granular materials like soil or snow are pushed together.
Brodu, along with physicists Robert Behringer of Duke University and Joshua Dijksman of Wageningen University in the Netherlands, describe how they use simple tools to measure the network of forces at it spreads from one particle to the next.
The researchers use a solution of hundreds of translucent hydrogel beads in a Plexiglass box to simulate materials like soil, sand or snow.
A piston repeatedly pushes down on the beads in the box while a sheet of laser light scans the box, and a camera takes a series of cross-sectional images of the illuminated sections.
Like MRI scans used in medicine, the technique works by converting these cross-sectional "slices" into a 3-D image.
Custom-built imaging software stacks the hundreds of thousands of 2-D images together to reconstruct the surface of each individual particle in three dimensions, over time. By measuring the tiny deformations in the particles as they are squeezed together, the researchers are able to calculate the forces between them.
The new approach will help researchers better understand a range of natural and manmade hazards, such as why farmworkers stepping into grain bins sometimes experience a quicksand effect and are suddenly sucked under.
"This gives us hope of understanding what happens in disasters like a landslide, when packed soil and rocks on a mountain become loose and slide down," Brodu said. "First it acts like a solid, and then for reasons physicists don't completely understand, all of a sudden it destabilizes and starts to flow like a liquid. This transition from solid to liquid can only be understood if you know what's going on inside the soil."
The team has already used results from their technique to create a new model for the way particulate matter behaves, which is concurrently published in the journal Physical Review E.
This research was supported by grants from the National Science Foundation (DMR1206351, DMS1248071), the National Aeronautics and Space Administration (NNX10AU01G), and the U.S. Army Research Office (W911NF-1-11-0110).
CITATION: "Spanning the Scales of Granular Materials through Microscopic Force Imaging," Brodu, N., J. A. Dijksman and R. P. Behringer. Nature Communications, March 2015. DOI: 10.1038/ncomms7361
Robin Ann Smith | EurekAlert!
Computer model predicts how fracturing metallic glass releases energy at the atomic level
20.07.2018 | American Institute of Physics
What happens when we heat the atomic lattice of a magnet all of a sudden?
18.07.2018 | Forschungsverbund Berlin
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
20.07.2018 | Power and Electrical Engineering
20.07.2018 | Information Technology
20.07.2018 | Materials Sciences