Featured Research

from universities, journals, and other organizations

New insight into how disordered solids deform

Date:
September 1, 2011
Source:
University of Pennsylvania
Summary:
In solid materials with regular atomic structures, figuring out weak points where the material will break under stress is relatively easy. But for disordered solids, like glass or sand, their disordered nature makes such predictions much more daunting tasks. Now, a collaboration combining a theoretical model with a first-of-its kind experiment has demonstrated a novel method for identifying "soft spots" in such materials.

In solid materials with regular atomic structures, figuring out weak points where the material will break under stress is relatively easy. But for disordered solids, like glass or sand, their disordered nature makes such predictions much more daunting tasks.

Related Articles


Now, a collaboration combining a theoretical model with a first-of-its kind experiment has demonstrated a novel method for identifying "soft spots" in such materials. The findings from University of Pennsylvania and Syracuse University physicists may lead to better understanding of the principles that govern materials responses ranging from failure of glasses to earthquakes and avalanches.

The experimental research was conducted by professors Arjun G. Yodh and Andrea J. Liu, along with post-doctoral associates Ke Chen, Wouter G. Ellenbroek and Zexin Zhang and graduate student Peter J. Yunker, all of the Department of Physics and Astronomy in Penn's School of Arts and Sciences. They collaborated with Lisa Manning of the Department of Physics at Syracuse. Liu and Manning described the theoretical model in a separate study.

Both studies appear in the journal Physical Review Letters.

For materials with well ordered, crystalline internal structures, such as diamonds or most metals, identifying soft spots is easy; weak, disordered sections stick out like a sore thumb.

"In perfect crystalline materials, atoms are in well-defined positions. If you give me the position of one atom, I can tell you the position of another with precision," Yodh said. "There's also a well defined theory about what's happening with defects in crystals when stresses are applied to them."

"There's no periodicity in glass, however," Chen said. "You can't look at it and say, 'This part looks different than the rest,' because there is no background pattern to compare it with."

With physical structure a dead end for identifying soft spots, the physicists turned to another property: vibrations. Though the word "solid" is synonymous with "unmoving," the particles that make up solid matter are constantly vibrating. And like the different tones of guitar strings, there are many different ways particles in a solid can vibrate. These are known as "vibration modes."

For crystalline materials, the regular patterns of atoms lead to uniform patterns of vibrations within the material; nearly all particles are involved in a typical vibration. In disordered materials, with their unevenly spaced particles, particles in different regions vibrate differently, producing some new and different vibration modes, particularly at low frequencies.

"We can determine the spatial patterns of the different vibrations in our experiment, and then we can find out whether some of them, particularly low frequency vibrations, are connected with rearrangements or failure of the material when it is stressed," Chen said.

Manning and Liu developed a simulation to test this kind of correlation under idealized conditions. They were able to show that certain regions highlighted by low frequency vibration modes acted like defects in disorganized materials and that these defects were good candidates for where the material would fail when stressed.

"We showed, for the first time, a correlation between the soft spot population and rearrangements under stress," Manning said. "This is something people have been looking for over the past 30 or 40 years."

Though the success of the simulation was an exciting result by itself, it was only a first step. Real-world systems have additional layers of complexity, notably temperature and related thermal fluctuations that can rapidly change the interactions between neighboring particles and thus the system's vibrational patterns.

"It was not at all obvious that the soft spots we found in the simulation would still exist in the presence of thermal fluctuations, which are unavoidable in the real world," Liu said. "Thermal fluctuations, for example, might have caused the soft spots to be wiped out too rapidly to be used for analysis."

To see if this was the case, Chen developed an experimental system with many features similar to the one in the simulation. At its core was a colloidal glass, an effectively two-dimensional material consisting of a single disordered layer of soft plastic particles tightly packed together.

By analyzing video of the particles' motion in the colloidal glass as observed under a microscope, Chen was able to calculate the vibration patterns and then use Manning and Liu's model to locate regions vulnerable to rearrangement once the glass was put under stress. He then compared these regions to the rearrangements that actually happened.

Just as in the simulation, the soft spots predicted candidates for rearrangement, as some of the identified soft spots remained intact while others deformed. The experiment thus provides a new basis -- low frequency vibration modes -- for analyzing real-world disordered solids.

"Low frequency vibrations correspond to areas with weak interaction between particles, and because of these weak interactions their structure is less stable. When they're perturbed there is less resistance from their neighbors." Chen said.

Disordered solids are much more common than ordered ones, so having a working theory of how, why and where they break has many potential applications.

"You can bend a metal spoon, but you can't bend one made out of glass without breaking it. If you can understand how disordered solids fail, you might be able to make them tougher," Yodh said.

The research was funded by the National Science Foundation, including the Penn Materials Research Science and Engineering Center, the Princeton Center for Theoretical Science at Princeton University, NASA and the U.S. Department of Energy.

Zexin Zhang has appointments with the CNRS-Rhodia-UPenn Complex Assemblies of Soft Matter collaboration and the Center for Soft Condensed Matter Physics and Interdisciplinary Research, Soochow University, China.


Story Source:

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


Journal References:

  1. Ke Chen, M. Manning, Peter Yunker, Wouter Ellenbroek, Zexin Zhang, Andrea Liu, A. Yodh. Measurement of Correlations between Low-Frequency Vibrational Modes and Particle Rearrangements in Quasi-Two-Dimensional Colloidal Glasses. Physical Review Letters, 2011; 107 (10) DOI: 10.1103/PhysRevLett.107.108301
  2. M. Manning, A. Liu. Vibrational Modes Identify Soft Spots in a Sheared Disordered Packing. Physical Review Letters, 2011; 107 (10) DOI: 10.1103/PhysRevLett.107.108302

Cite This Page:

University of Pennsylvania. "New insight into how disordered solids deform." ScienceDaily. ScienceDaily, 1 September 2011. <www.sciencedaily.com/releases/2011/08/110831160228.htm>.
University of Pennsylvania. (2011, September 1). New insight into how disordered solids deform. ScienceDaily. Retrieved November 25, 2014 from www.sciencedaily.com/releases/2011/08/110831160228.htm
University of Pennsylvania. "New insight into how disordered solids deform." ScienceDaily. www.sciencedaily.com/releases/2011/08/110831160228.htm (accessed November 25, 2014).

Share This


More From ScienceDaily



More Matter & Energy News

Tuesday, November 25, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Who Will Failed Nuclear Talks Hurt Most?

Who Will Failed Nuclear Talks Hurt Most?

Reuters - Business Video Online (Nov. 25, 2014) With no immediate prospect of sanctions relief for Iran, and no solid progress in negotiations with the West over the country's nuclear programme, Ciara Lee asks why talks have still not produced results and what a resolution would mean for both parties. Video provided by Reuters
Powered by NewsLook.com
Flying Enthusiast Converts Real-Life Aircraft Cockpit Into Simulator

Flying Enthusiast Converts Real-Life Aircraft Cockpit Into Simulator

Reuters - Innovations Video Online (Nov. 25, 2014) A virtual flying enthusiast converts parts of a written-off Airbus aircraft into a working flight simulator in his northern Slovenian home. Jim Drury reports. Video provided by Reuters
Powered by NewsLook.com
Car Park Solution for Flexible Green Energy

Car Park Solution for Flexible Green Energy

Reuters - Innovations Video Online (Nov. 24, 2014) A British solar power start-up says that by covering millions of existing car park spaces around the UK with flexible solar panels, the country's power problems could be solved. Suzannah Butcher reports. Video provided by Reuters
Powered by NewsLook.com
Microsoft Adds Robot Guards, Ushers In Sci-Fi Apocalypse

Microsoft Adds Robot Guards, Ushers In Sci-Fi Apocalypse

Newsy (Nov. 23, 2014) Microsoft has robotic security guards working at its Silicon Valley Campus. Video provided by Newsy
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:

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