Smallest earthquakes ever detected on micron scale minerals

At the micrometer scale, the deformation properties of metals change profoundly: the smooth and continuous behavior of bulk materials often becomes jerky due to random stress bursts of different sizes. Credit: Peter Dusan Espanovetti and David Ogi

At the micrometer scale, the deformation properties of metals change profoundly: the smooth and continuous behavior of bulk materials often becomes jerky due to random stress bursts of different sizes. This phenomenon is caused by the complex discontinuous redistribution of lattice dislocations (streak-like crystal defects responsible for the irreversible deformation of crystalline materials) due to external loading, which is also the reason for the formation of the uneven, grade-like surface upon deformation.

To study this phenomenon in more detail, research groups from Eötvös Loránd University in Budapest, Charles University of Prague and École des Mines de Saint-Étienne have developed a highly precise mechanical platform, in which weak elastic waves emitted by the sample can be detected during the deformation of micron-scale columns. Compression experiments with such a zinc monocrystalline micropillar in a scanning electron microscope confirmed that these so-called acoustic signals do indeed occur during stress bursts, so this experiment allowed us, for the first time, to hear the “sound of turbulence” in practice.

Audio signals are sampled at 2.5 MHz; Therefore, they provide very detailed information on the dynamics of disturbances. In-depth statistical analyzes by the researchers revealed that stress bursts exhibit a two-level structure: what so far is perceived as a single plastic slip is, in fact, the result of many correlated events on a μs-ms time scale.

The reason for this phenomenon is the complex and discontinuous redistribution of retinal dislocations (line-like cyst defects responsible for the irreversible deformation of crystalline materials) due to external loading, which is also the reason for the formation of the uneven, grade-like surface upon deformation. Credit: Peter Dusan Espanovetti and David Ogi

The most surprising result from the experiments is that this process, despite the fundamental differences between the mechanisms of mineral deformation and those of plate tectonics, is found to be quite similar to earthquakes.

The acoustic signals emitted by the test pieces followed basic empirical laws established for major and aftershocks in seismology, such as the Gutenberg-Richter and Aomori laws.

said Peter Dusan Espanofti, Associate Professor at Ifos Lorand University and Head of the Department of Micromechanics and Multiscale Modeling Research Group. “As acoustic emission measurement is a frequent method for monitoring and locating physical failures in technological applications, by providing fundamentally new information about the fundamental physics, our results are expected to contribute to the further development of this technology.”

Zinc micropolar pressure. Ultrasound acoustic signals were otherwise transduced into the audible field to better elucidate the relationship between acoustic events and stress bursts. Credit: Eötvös Loránd University (ELTE), Faculty of Science

David Augie, Ph.D. A student in Ispánovity’s group and corresponding author of the publication added, “These experiments are rather complicated, as one has to pair a nanometer-resolution processing instrument with a highly sensitive acoustic sensor, all in the vacuum chamber of a scanning electron microscope. Such measurements, as far as we know, It can currently only be performed in 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, published in Nature Communications, are expected to open new horizons in the search for precise mechanical properties of materials.

Spin-sonics: sound wave makes electrons spin More information: Péter Dusán Ispánovity et al, Avalanches are like earthquakes on the micron scale, Nature Communications (2022). DOI: 10.1038 / s41467-022-29044-7 Provided by Eötvös Loránd University

Quote: Smallest earthquakes ever detected in micron-scale minerals (2022, Apr 14) Retrieved Apr 14, 2022 from https://phys.org/news/2022-04-smallest-earthquakes-micron-scale-metals .html

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