Researchers listen for failure in granular materials

May 29, 2018 by Tracey Peake, North Carolina State University
False-color image of sheared grains. Credit: Ted Brzinski

In a pilot study, researchers from North Carolina State University and Haverford College have used naturally arising acoustic vibrations—or sound waves—to monitor the state of granular materials. This passive approach represents a way to probe disordered or granular materials without disturbing them, and may enable researchers to forecast the failure of these materials.

Granular materials, like the ground beneath us, can fail through spontaneous events like earthquakes. But it is difficult to probe or measure these materials in order to predict . Haverford College physicist and former NC State postdoctoral researcher Ted Brzinski and NC State physicist Karen Daniels decided to examine sound waves emanating from the material to characterize the different vibrational modes of the material.

Vibrational modes are the ways in which something can oscillate, or move internally. A small molecule can only oscillate in a few ways, for example, but larger objects will have more modes, which are affected by both the locations and the masses of the components. In a disordered or amorphous system of granular materials, like dirt or gravel, the number of modes quickly becomes too large to either predict or measure directly.

However, each mode has a particular acoustic frequency associated with it. Brzinski and Daniels' approach measures the frequencies of the active vibrational modes in the material, giving them an acoustic snapshot of the material's overall "health."

To test their technique they created a granular system composed of 8,000 circular and elliptical polymer beads. They recorded the acoustic emissions from over 1,100 stick-slip events—which is what happens when tectonic plates slide past each other in an earthquake—and classified the frequencies present in acoustic signals associated with impending failure.

"Lower frequencies are associated with 'floppy' modes, meaning that there is a lot more movement, while higher frequencies are associated with stiff or rigid modes," says Brzinski. "What people have seen in model systems is that as you have more floppy modes than expected, the closer you are to losing rigidity. The slip occurs when rigidity is lost. Our tests confirmed these model system results—failures occurred when there were more low frequency modes than expected."

"But it's not just listening to see what sound frequencies are present; we need to look at the proportion of modes," says Daniels. "We know that materials close to failure have a lot of low modes. Our method counts the numbers of certain types of modes in order to predict failure. The beauty of the technique is that you can monitor the system without any interference—just by listening. The method is fairly simple, and it may let us forecast the behavior of disordered ."

The research appears in Physical Review Letters.

Explore further: Acoustic emissions unveil internal motion in granular materials

More information: Theodore A. Brzinski et al, Sounds of Failure: Passive Acoustic Measurements of Excited Vibrational Modes, Physical Review Letters (2018). DOI: 10.1103/PhysRevLett.120.218003

Related Stories

Drum beats from a one atom thick graphite membrane

June 14, 2016

Researchers from the Tata Institute of Fundamental Research, Mumbai, have demonstrated the ability to manipulate the vibrations of a drum of nanometre scale thickness - realizing the world's smallest and most versatile drum. ...

Force is the key to granular state-shifting

February 15, 2013

Ever wonder why sand can both run through an hourglass like a liquid and be solid enough to support buildings? It's because granular materials – like sand or dirt – can change their behavior, or state. Researchers from ...

The synchronized dance of skyrmion spins

May 30, 2017

In recent years, excitement has swirled around a type of quasi-particle called a skyrmion that arises as a collective behavior of a group of electrons. Because they're stable, only a few nanometers in size, and need just ...

Do cells have exotic vibrational properties?

February 28, 2017

A little-understood biological property that appears to allow cell components to store energy on their outer edges is the possible key to developing a new class of materials and devices to collect, store and manage energy ...

Recommended for you

Correlated nucleons may solve 35-year-old mystery

February 20, 2019

A careful re-analysis of data taken at the Department of Energy's Thomas Jefferson National Accelerator Facility has revealed a possible link between correlated protons and neutrons in the nucleus and a 35-year-old mystery. ...

CMS gets first result using largest-ever LHC data sample

February 15, 2019

Just under three months after the final proton–proton collisions from the Large Hadron Collider (LHC)'s second run (Run 2), the CMS collaboration has submitted its first paper based on the full LHC dataset collected in ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet May 30, 2018
Is this related to 'Singing' dunes ??

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.