Acoustic emissions unveil internal motion in granular materials

Feb 07, 2014

When confronted with a heavy load or deformed by stress, the individual particles in a granular material will sometimes reorganize to a more stable arrangement. At small scales these reorganizations are little more than the redistribution of grains in the pile. In some cases, though, a reorganization is the first step of a critical failure, the trigger for an avalanche or landslide.

Understanding how the motion of individual grains translates into mass movement requires having a way to peer inside the pile without interfering with its behavior. Through a series of experiments, Michlmayr et al. find that specially tuned vibration sensors could be used to listen in on grain-scale dynamics. They find that elastic waves of different frequencies can be used to track and measure different types of motion within a .

In their experiments, the authors stressed granular with varying grain sizes. They find that when subjected to a constant deformation, stresses in the materials oscillate in a sawtooth pattern—increasing steadily before dropping suddenly. The drops in shear stress—the sign of a reorganization—correlate with observations of low-frequency acoustic emissions. Materials with smaller grain sizes experience more frequent but less powerful stress drops than those with larger grain sizes. Observations of high-frequency acoustic emissions, the authors find, were associated with grain-on-grain interactions.

Explore further: Africa, from a CATS point of view

More information: Shear induced force fluctuations and acoustic emissions in granular material, Journal of Geophysical Research-Solid Earth, DOI: 10.1002/2012JB009987, 2013 http://onlinelibrary.wiley.com/doi/10.1002/2012JB009987/abstract

add to favorites email to friend print save as pdf

Related Stories

Characterizing solar cells with nanoscale precision

Dec 05, 2013

(Phys.org) —Researchers from the NIST Center for Nanoscale Science and Technology (CNST) have demonstrated a new low energy electron beam technique and used it to probe the nanoscale electronic properties ...

Nanocrystals not small enough to avoid defects

Dec 14, 2012

(Phys.org)—Nanocrystals as protective coatings for advanced gas turbine and jet engines are receiving a lot of attention for their many advantageous mechanical properties, including their resistance to ...

What does 'whole grain' really mean?

Feb 05, 2014

The most comprehensive definition of whole grain termed to date has been published this week in the journal Food and Nutrition Research. The effort to create the definition, which is intended to assist in the production and ...

Recommended for you

Africa, from a CATS point of view

1 hour ago

From Saharan dust storms to icy clouds to smoke on the opposite side of the continent, the first image from NASA's newest cloud- and aerosol-measuring instrument provides a profile of the atmosphere above ...

Climate change may flatten famed surfing waves

Feb 25, 2015

On a summer day in 1885, three Hawaiian princes surfed at the mouth of the San Lorenzo River on crudely constructed boards made from coastal redwoods, bringing the sport to the North American mainland.

User comments : 0

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.