Featured Research

from universities, journals, and other organizations

Stress causes clogs in coffee and coal

Date:
December 14, 2011
Source:
Duke University
Summary:
Scientists still aren't sure what causes clogs in flowing macroscopic particles, like corn, coffee beans and coal chunks. But new experiments suggest that when particles undergo a force called shear strain, they jam sooner than expected.

It's easy to get in a jam. But it's much harder to explain exactly how or when it started.

Related Articles


Scientists still aren't sure what causes clogs in flowing macroscopic particles, like corn, coffee beans and coal chunks. But new experiments by Duke physicist Robert Behringer and his colleagues suggest that when particles undergo a force called shear strain, they jam sooner than expected. The results appear in the Dec. 15 issue of Nature.

Shear strain is sort of like cupping sand between your hands, and then, without changing the width between them, moving one hand forward and the other hand backward, Behringer said. Not much sand flows between your hands with a force like this.

Many flows, including those of nuts, coffee and coal, inherently produce this type of movement among grains, but the design and engineering for hoppers and other dispensers that don't account for it won't work well, Behringer said.

The new work "points out the deficiencies in our current theoretical framework for when granular materials jam," said Corey O'Hern, an expert in granular media at Yale University who was not involved in the new study.

A deeper understanding of this point will lead to the design of new composite granular matter and also to the development of advanced materials that could counter weapons of mass destruction, including amplifiers and other countermeasures for deflecting blast waves, he said.

In past studies, physicists calculating how grains flow estimated their jamming point without accounting for friction forces among individual particles. Eliminating friction makes jamming easier to explain mathematically. It also suggested that just an increase in density would cause granular materials to jam.

"It's been an uphill battle to convince the scientific community that friction is important, and that shear causes jamming where it was not expected. No other experimentalists have really looked at what's happening with both friction and shear," Behringer said.

In his new experiments, Behringer and his team controlled the number of discs placed in a box designed to produce a shear strain. The researchers applied the shearing strain while allowing the discs to flow where they wanted.

The discs had distinct properties that allowed the team to measure the force each one experienced due to friction and shearing. The team also took pictures showing how those forces developed into branched chains, which spread through many discs and ultimately block their flow. The images and experiments show that because of friction forces and shear strain, the discs jammed when they were much farther apart, or at a lower density, than what had been previously predicted.

It's not just the number of particles that put them in a jam, it's also the strain and the real-world forces, like friction, that cause the back-up, Behringer said. The discovery could change the design of coal and grain silos and even the bulk dispensers at Whole Foods.

Friction and shear reveal the richness of possible states of granular matter, pointing scientists down a road paved with new discoveries, said Daryl Hess, program director for condensed matter and materials theory at NSF. Studying these new states of granular matter may also expose deeper connections between jamming and seemingly unrelated phenomena, from earthquakes to transformations occurring in other kinds of matter, like water to ice, he said.


Story Source:

The above story is based on materials provided by Duke University. Note: Materials may be edited for content and length.


Journal Reference:

  1. Dapeng Bi, Jie Zhang, Bulbul Chakraborty, R. P. Behringer. Jamming by shear. Nature, 2011; 480 (7377): 355 DOI: 10.1038/nature10667

Cite This Page:

Duke University. "Stress causes clogs in coffee and coal." ScienceDaily. ScienceDaily, 14 December 2011. <www.sciencedaily.com/releases/2011/12/111214135746.htm>.
Duke University. (2011, December 14). Stress causes clogs in coffee and coal. ScienceDaily. Retrieved October 24, 2014 from www.sciencedaily.com/releases/2011/12/111214135746.htm
Duke University. "Stress causes clogs in coffee and coal." ScienceDaily. www.sciencedaily.com/releases/2011/12/111214135746.htm (accessed October 24, 2014).

Share This



More Matter & Energy News

Friday, October 24, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

3D Printed Instruments Make Sweet Music in Sweden

3D Printed Instruments Make Sweet Music in Sweden

Reuters - Innovations Video Online (Oct. 23, 2014) — Students from Lund University's Malmo Academy of Music are believed to be the world's first band to all use 3D printed instruments. The guitar, bass guitar, keyboard and drums were built by Olaf Diegel, professor of product development, who says 3D printing allows musicians to design an instrument to their exact specifications. Matthew Stock reports. Video provided by Reuters
Powered by NewsLook.com
Chameleon Camouflage to Give Tanks Cloaking Capabilities

Chameleon Camouflage to Give Tanks Cloaking Capabilities

Reuters - Innovations Video Online (Oct. 22, 2014) — Inspired by the way a chameleon changes its colour to disguise itself; scientists in Poland want to replace traditional camouflage paint with thousands of electrochromic plates that will continuously change colour to blend with its surroundings. The first PL-01 concept tank prototype will be tested within a few years, with scientists predicting that a similar technology could even be woven into the fabric of a soldiers' clothing making them virtually invisible to the naked eye. Matthew Stock reports. Video provided by Reuters
Powered by NewsLook.com
Jet Sales Lift Boeing Profit 18 Pct.

Jet Sales Lift Boeing Profit 18 Pct.

Reuters - Business Video Online (Oct. 22, 2014) — Strong jet demand has pushed Boeing to raise its profit forecast for the third time, but analysts were disappointed by its small cash flow. Fred Katayama reports. Video provided by Reuters
Powered by NewsLook.com
Internet of Things Aims to Smarten Your Life

Internet of Things Aims to Smarten Your Life

AP (Oct. 22, 2014) — As more and more Bluetooth-enabled devices are reaching consumers, developers are busy connecting them together as part of the Internet of Things. (Oct. 22) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:

More Coverage


How Granular Materials Become Solid: Discovery May Be Boon to Engineers, Manufacturers

Dec. 14, 2011 — What is it is that makes granular materials change from a flowing loose state to a "jammed," or solid, state? Researchers can now explain how granular materials are transformed when force ... read more

Strange & Offbeat Stories

 

Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins