Subscribe to our free daily newsletters
. 24/7 Space News .




Subscribe to our free daily newsletters



TECH SPACE
Metal defects can be eliminated by cyclic loading
by Staff Writers
Boston MA 9SPX) Oct 23, 2015


This image shows abrupt de-pinning and de-stabilization of a line defect due to repeated cyclic loading. Figure (a) shows the evolution of nominal tensile stress during two loading and unloading cycles. Figures (b) to (f) are still frames from a video that correspond to the stress state marked in (a), where the white dashed lines indicate the original defect location, and the colored dashed lines represent the altered locations from cyclic loading. The direction of tensile stretching is indicated by the arrows in figures (c) and (e). Image courtesy Zhangjie Wang, Zhiwei Shan, Ming Dao, and Subra Suresh.

It's a well-known characteristic of metals that repeated bending in the same place can cause the material to weaken and eventually break; this phenomenon, known as metal fatigue, can cause serious damage to metal components subjected to repeated stress.

But now, researchers from MIT, Carnegie Mellon University, Xi'an Jiaotong University, and elsewhere have found that under certain conditions, repeated slight stretching of nanoscale metal pieces can actually strengthen a material by eliminating defects in its crystalline structure.

The new finding is reported this week in the Proceedings of the National Academy of Sciences, in a paper co-authored by MIT's Ming Dao and Ju Li, Subra Suresh of Carnegie Mellon, Zhiwei Shan of Xi'an Jiaotong University, and others in China and at Johns Hopkins University. They refer to the new process as "cyclic healing."

"While metal fatigue has been studied extensively at larger volumes of materials, there has been little understanding of it at atomic scale," says Dao, a principal research scientist in MIT's Department of Materials Science and Engineering. To remedy that, the team decided to study the fatigue of metal using a transmission electron microscope to observe atomic-scale changes in defects.

The team primarily studied what happens in small, single-crystal pieces of aluminum. They aimed to reduce or eliminate microstructural imperfections - such as defects in the crystal lattice known as "dislocations" - through repeated, small-amplitude, cyclic deformation, rather than heat-based annealing.

The researchers found that repeated small displacements of the metal tend to dislodge the dislocations from their pinned locations inside the crystal. The small crystal has a high surface to volume ratio, so the dislocations are attracted to the surface - and the energy stored in the metal due to the presence of the defects could be reduced. "Eventually, these defects can be driven all the way out to the surface," Dao says.

By "shaking" the dislocations gently and repeatedly, the researchers were able to get the material relatively free of them; consequently, the material's strength increased significantly. This phenomenon is counterintuitive, because it is the opposite of what one sees in much larger metal crystals, where repeated stretching often increases defect density and causes cracks to form.

The process could help in the production of strong parts for nanotechnology applications, such as mechanical nanosensors, nanoelectromechanical systems, and nanorobots.

"This work demonstrates how cyclic deformation, under certain controlled conditions, can lead to the removal of defects from crystals of small volume," says Suresh, Carnegie Mellon's president and a professor emeritus of materials science and engineering and former dean of engineering at MIT.

"In addition to pointing out how these mechanisms of cyclic deformation can be very different from those seen in larger-volume materials, this work also offers new avenues for eliminating defects from crystals without the need for thermal treatment or shape change.

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

.


Related Links
Massachusetts Institute of Technology
Space Technology News - Applications and Research






Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

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

Previous Report
TECH SPACE
Mother-of-pearl's genesis identified in mineral's transformation
Madison WI (SPX) Oct 22, 2015
How nature makes its biominerals - things like teeth, bone and seashells - is a playbook scientists have long been trying to read. Among the most intriguing biominerals is nacre, or mother-of-pearl - the silky, iridescent, tougher-than-rock composite that lines the shells of some mollusks and coats actual pearls. The material has been worked by humans for millennia to make everything from button ... read more


TECH SPACE
Watch worn by US astronaut on Moon sells for $1.6 mn

Europe-Russia Lunar mission will make them friends again

Mound near lunar south pole formed by unique volcanic process

Lunar Pox

TECH SPACE
Landing site recommended for ExoMars 2018

You too can learn to farm on Mars

The Martian Astrobiologist

Opportunity parked for solar panels to charge up for winter

TECH SPACE
The Study of Science through Popular Movies

Reentry data will help improve prediction models

Hold on to your hoverboard: 'Back to the Future' is now

Journaling: Astronauts chronicle missions

TECH SPACE
The Last Tiangong

China aims to go deeper into space

Latest Mars film bespeaks potential of China-U.S. space cooperation

Exhibition on "father of Chinese rocketry" opens in U.S.

TECH SPACE
RSC Energia patented inflatable space module for ISS

Clearing the Space Fog on ISS

International Space Agencies Meet to Advance Space Exploration

Meet the International Docking Adapter

TECH SPACE
Ariane 5 is delivered for Arianespace's sixth heavy-lift mission of 2015

ORBCOMM Announces Launch Window For Second OG2 Mission

10th Anniversary of the Final Titan

China puts new communication satellite into orbit for HK company

TECH SPACE
NASA's K2 Finds Dead Star Vaporizing a Mini 'Planet'

Cosmic 'Death Star' is destroying a planet

Most earth-like worlds have yet to be born, according to theoretical study

Airbus DS ready to start testing exoplanet tracker CHEOPS

TECH SPACE
Nanoscale diamond 'racetrack' becomes breakthrough Raman laser

Deutsche Telekom, Huawei in cloud link to rival Amazon

Ukraine to receive U.S. radars by mid-November

Metal defects can be eliminated by cyclic loading




Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News






The content herein, unless otherwise known to be public domain, are Copyright 1995-2017 - 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. Privacy Statement