. 24/7 Space News .
Penn researchers establish universal signature fundamental to how glassy materials fail
by Staff Writers
Philadelphia PA (SPX) Dec 11, 2017

Snapshots of softness fields and particle arrangements for the oligomer pillar simulation and the granular pillar experiment, two of the systems investigated in the paper.

Dropping a smartphone on its glass screen, which is made of atoms jammed together with no discernible order, could result in it shattering. Unlike metals and other crystalline material, glass and many other disordered solids cannot be deformed significantly before failing and, because of their lack of crystalline order, it is difficult to predict which atoms would change during failure.

"In order to understand how a system chooses its rearrangement scenario," said Douglas Durian, professor of physics and astronomy at the University of Pennsylvania, "we must make connection with the underlying microscopic structure. For crystals, it's easy; rearrangements are at topological defects such as dislocations. For disordered solids, it's a very hard 40-year-old problem that we're now cracking: What and where are structural defects in something that's disordered?"

To find a link between seemingly disparate disordered materials, an interdisciplinary collaboration between Penn researchers in the School of Arts and Sciences and the School of Engineering and Applied Science with expertise in various materials studied an unprecedented range of disordered solids with constituent particles ranging from individual atoms to river rocks. Understanding materials failure on a fundamental level could pave the way for designing more shatter-resistant glasses or predicting geological phenomena like landslides.

In a paper published in Science, the Penn researchers revealed commonalities among these disordered systems, defining a counterpart to the "defects" implicated in crystalline materials failure. This so-called "softness" in disordered systems predicts the location of defects, which are the collection of particles most likely to change when the material fails.

The researchers used a technique developed by Durian with Penn Ph.D. graduate Samuel Schoenholz, and Harvard University Ph.D. graduate Ekin Dogus Cubuk, both currently at Google Brain; Andrea Liu, Hepburn Professor of Physics in Penn's School of Arts and Sciences; and Efthimios Kaxiras, John Hasbrouck Van Vleck Professor of Pure and Applied Physics, Harvard School of Engineering and Applied Sciences.

Liu and Daniel Gianola, then a professor in Penn's School of Engineering and Applied Science's Department of Materials Science and Engineering and now at the University of California, Santa Barbara, led the study. Daniel Strickland and Robert Ivancic, both graduate students at Penn, are first authors, together with Cubuk and Schoenholz.

The paper is the culmination of years of research conducted at Penn's Materials Research Science and Engineering Center (MRSEC) which is hosted by the Laboratory for Research on the Structure of Matter. Liu and Robert Carpick, John Henry Towne Professor and chair in Mechanical Engineering and Applied Mechanics at Penn were co-leaders of the MRSEC's integrated research group focused on the mechanics of disordered packings.

A dozen of the group's faculty members, along with students and postdoctoral researchers from their labs, contributed to the study, providing data from 15 simulations and experiments on different types of disordered systems. The particles in those systems ranged in size from carbon atoms that make up wear-resistant engine coatings to centimeter-sized plastic spheres in a model riverbed.

Using machine learning, the researchers collected hundreds of quantities that characterize the arrangements of particles in each system, quantities that individually might not be expected to reveal much. Importantly, they found the combination of these quantities that correlates strongly with the dynamics. This produced a microscopic structural property called softness. If softness is known, the behavior of the disordered material and how likely its constituent particles are to rearrange can be predicted.

The systems the researchers studied were rearranging due to random thermal fluctuations or to different kinds of applied stress such as squeezing or stretching. In all cases, the technique worked well, and the researchers were able to predict with high accuracy the probability that the systems would rearrange.

The researchers then compared properties across systems. They found that the length scale over which softness was correlated was identical to the size of rearrangements, or the number of particles that move when failure occurs. Remarkably, they found that this number is almost identical in all of these systems regardless of the size of the particles and how they interact.

"People have been talking about what sets the size of localized rearrangements in disordered solids for 40 years," Liu said.

"They speculated about localized defects that they called shear transformation zones in disordered systems where rearrangements are likely to occur, but no one had seen this directly. They couldn't predict ahead of time where rearrangements would be likely to occur. With the machine learning, we're saying, 'Let's train the system. Let's look at the rearrangements and the structures and see if we can figure out what's important and then use that.' It's conceptually very straightforward, but it turns out to be very powerful."

The researchers also measured the yield strain, or how much the solid can be deformed before it starts to plastically deform. They also found that the yield strain is approximately the same for all disordered solids over systems spanning 13 orders of magnitude in their mechanical stiffness. By comparison, the yield strains for different crystalline materials can vary by a hundred- or thousand-fold.

Now that the researchers have shown that, up to and around when stress is applied, all these systems look the same, the next step of the effort is co-led by Durian and Paulo Arratia, professor of mechanical engineering and applied mechanics in the School of Engineering and Applied Science.

Their goal is to go beyond yield, where all becomes chaos and the systems begin to look extremely different. Some systems fracture, others show shear bands and others, like foams, can smoothly flow forever.

"When a rearrangement happens, the softnesses of the nearby particles all change," Durian said, "but, due to long-range elastic couplings, so can the softnesses of particles even quite far away, as illustrated by this data.

Thus, a rearrangement has a nontrivial effect on where the next rearrangements are likely to occur. In particular, will nearby rearrangements be encouraged and hence promote shear banding, or will they be discouraged and hence promote toughness? We believe that understanding and ultimately controlling the complex interplay between rearrangements, stress, and structure - here quantified by softness - is the key to improving toughness."

If the researchers can understand why different systems behave differently beyond yield, they may be able to control softness and how it evolves when it's under stress. This could lead to tougher coatings and materials, such as more durable glass screens for phones.

"Disordered solids have a lot of great properties," Liu said. "You can mold them into any shape you want or create surfaces that are atomically smooth, which you can't really do with crystalline systems. But they tend to shatter easily. If we can understand what controls that and how to prevent it, then the concepts start to have real applications. In an ideal case, we want to develop new, tougher materials that aren't as brittle or don't fall apart as catastrophically."

Research paper

New microscope sets a record for visualizing surface wetting properties
Helsinki, Finland (SPX) Dec 05, 2017
Wetting is an everyday phenomenon that represents how well liquid spreads on a surface. When water comes into contact with an extremely water-repellent, or 'superhydrophobic' surface, droplets bead up and roll off easily. Aalto University researchers have developed a measurement technique called Scanning Droplet Adhesion Microscopy (SDAM) to understand and characterize the wetting properti ... read more

Related Links
University of Pennsylvania
Space Technology News - Applications and Research

Thanks for being there;
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 Monthly Supporter
$5+ Billed Monthly

paypal only
SpaceDaily Contributor
$5 Billed Once

credit card or paypal

Comment using your Disqus, Facebook, Google or Twitter login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle

Tech titans ramp up tools to win over children

Aerospace and Mitchell Institute release new report on policy needs for space operations

UAE launches programme to send astronauts into space

China pushed global patent filings to record high in 2016: UN

SpaceX's Elon Musk to launch his own car into deep space

ISRO eyes one rocket launch a month in 2018

Russia to build launch pad for super heavy-lift carrier by 2028

Flat-Earther's self-launch plan hits a snag

EU exempts fuel for ExoMars mission from Russian sanctions

Mars Rover Team's Tilted Winter Strategy Works

Brown: Clay on Mars May Have Formed in Primordial Steam Bath

Winter wanderings put Opportunity at 28 Miles on the odometer

Nation 'leads world' in remote sensing technology

China plans for nuclear-powered interplanetary capacity by 2040

China plans first sea based launch by 2018

China's reusable spacecraft to be launched in 2020

Regulation and compliance for nontraditional space missions

Orbital ATK purchase by Northrop Grumman approved by shareholders

UK space launch program receives funding boost from Westminster

Going green to the Red Planet

Penn researchers establish universal signature fundamental to how glassy materials fail

In first, 3-D printed objects connect to WiFi without electronics

Better mastery of heat flow leads to next-generation thermal cloaks

3-D-printed minifactories

Two Super-Earths around red dwarf K2-18

A New Spin to Solving Mystery of Stellar Companions

The CHEOPS scientific instrument is complete

Discovery about rare nitrogen molecules offers clues to makeup of life-supporting planets

Wrapping up 2017 one year out from MU69

Jupiter Blues

Research bolsters possibility of plate tectonics on Europa

Pluto's hydrocarbon haze keeps dwarf planet colder than expected

The content herein, unless otherwise known to be public domain, are Copyright 1995-2024 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. All articles labeled "by Staff Writers" include reports supplied to Space Media Network by industry news wires, PR agencies, corporate press officers and the like. Such articles are individually curated and edited by Space Media Network staff on the basis of the report's information value to our industry and professional readership. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. General Data Protection Regulation (GDPR) Statement Our advertisers use various cookies and the like to deliver the best ad banner available at one time. All network advertising suppliers have GDPR policies (Legitimate Interest) that conform with EU regulations for data collection. By using our websites you consent to cookie based advertising. If you do not agree with this then you must stop using the websites from May 25, 2018. Privacy Statement. Additional information can be found here at About Us.