On the micrometer scale deformation properties of metals change profoundly: the smooth and continuous behaviour of bulk materials often becomes jerky due to random strain bursts of various sizes. The reason for this phenomenon is the complex intermittent redistribution of lattice dislocations (which are line-like ctystal defects responsible for the irreversible deformation of crystalline materials) due to external loading, which is also the cause of the formation of the uneven step-like surface upon deformation.

To study this phenomenon in more detail, research groups of the Eotvos Lorand University of Budapest, Charles University of Prague and Ecole des Mines de Saint-Etienne have developed a highly sensitive micromechanical platform, where weak elastic waves emitted by the specimen can be detected during the deformation of micron-scale pillars. Compression experiments performed on such zinc single crystalline micropillars in a scanning electron microscope confirmed that these so-called acoustic signals indeed occur during strain bursts, so, this experiment allowed us, for the first time, to practically hear the "sound of dislocations".

The acoustic signals are sampled with a rate of 2.5 MHz, therefore, they provide extremely detailed information on the dynamics of dislocations. The in-depth statistical analyses performed by the researchers revealed that strain bursts exhibit a two-level structure: what has so far been seen as a single plastic slip is, in fact, a result of several correlated events on a us-ms timescale.

The most surprising outcome of the experiments is that this process, despite the fundamental differences between deformation mechanisms of metals and that of tectonic plates, was found to be completely analogous to earthquakes.

Acoustic signals emitted from the testpieces followed fundamental empirical laws established for main shocks and aftershocks in seismology, such as the Gutenberg-Richter and Omori laws.

"These results are expected to bear high technological impact since, for the first time, we were able to observe direct connection between acoustic signals and the plastic events that emitted them" said Peter Dusan Ispanovity, assistant professor at Eovos Lorand University and head of the Micromechanics and Multiscale Modelling Research Group. "Since the measurement of acoustic emission is a frequent method for monitoring and locating material failure in technological applications, by providing fundamentally new information about the underlying physics our results are expected to contribure to the further development of this technique."

David Ugi, PhD student in the group of Ispanovity and corresponding author of the publication added: "These experiments are rather complex, since one has to couple the nanometer precision manipulation tool with the extremely sensitive acoustic sensor, all in the vacuum chamber of a scanning electron microscope.

Such measurements, to our knowledge, at the moment can only be performed at our laboratory" added the young researcher.

The methodology can also be used to investigate other types of deformation mechanisms, such as twinning or fracture, so the results, which were published in Nature Communications, are expected to open up new vistas in the research of micromechanical propeties of materials.

Research Report:"Dislocation avalanches are like earthquakes on the micron scale"

Related Links
Faculty of Science - ELTE
Space Technology News - Applications and Research

Tweet

Thanks for being here; We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain. With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords. Our news coverage takes time and effort to publish 365 days a year. If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.
SpaceDaily Contributor $5 Billed Once credit card or paypal		SpaceDaily Monthly Supporter $5 Billed Monthly paypal only

Embracing ancient materials and 21st-century challenges
Boston MA (SPX) Apr 14, 2022
When Sophia Mittman was 10 years old, she wanted to be an artist. But instead of using paint, she preferred the mud in her backyard. She sculpted it into pots and bowls like the ones she had seen at the archaeological museums, transforming the earthly material into something beautiful. Now an MIT senior studying materials science and engineering, Mittman seeks modern applications for sustainable materials in ways that benefit the community around her. Growing up in San Diego, California, Mit ... read more