Subscribe free to our newsletters via your
. 24/7 Space News .

Subscribe free to our newsletters via your

Conquering metal fatigue
by Staff Writers
Boston MA (SPX) Mar 13, 2017

Researchers have developed a type of steel with three characteristics that help it resist microcracks that lead to fatigue failure: a layered nanostructure, a mixture of microstructural phases with different degrees of hardness, and a metastable composition. They compared samples of metal with just one or two of these key attributes (top left, top right, and bottom left) and with all three (bottom right). The metal alloy with all three attributes outperformed all the others in crack resistance. Image courtesy of the researchers.

Metal fatigue can lead to abrupt and sometimes catastrophic failures in parts that undergo repeated loading, or stress. It's a major cause of failure in structural components of everything from aircraft and spacecraft to bridges and powerplants. As a result, such structures are typically built with wide safety margins that add to costs.

Now, a team of researchers at MIT and in Japan and Germany has found a way to greatly reduce the effects of fatigue by incorporating a laminated nanostructure into the steel. The layered structuring gives the steel a kind of bone-like resilience, allowing it to deform without allowing the spread of microcracks that can lead to fatigue failure.

The findings are described in a paper in the journal Science by C. Cem Tasan, the Thomas B. King Career Development Professor of Metallurgy at MIT; Meimei Wang, a postdoc in his group; and six others at Kyushu University in Japan and the Max Planck Institute in Germany.

"Loads on structural components tend to be cyclic," Tasan says.

For example, an airplane goes through repeated pressurization changes during every flight, and components of many devices repeatedly expand and contract due to heating and cooling cycles. While such effects typically are far below the kinds of loads that would cause metals to change shape permanently or fail immediately, they can cause the formation of microcracks, which over repeated cycles of stress spread a bit further and wider, ultimately creating enough of a weak area that the whole piece can fracture suddenly.

"A majority of unexpected failures [of structural metal parts] are due to fatigue," Tasan says. For this reason, large safety factors are used in component design, leading to increased costs during production and component life.

Tasan and his team were inspired by the way nature addresses the same kind of problem, making bones lightweight but very resistant to crack propagation. A major factor in bone's fracture resistance is its hierarchical mechanical structure, so the team investigated microstructures that would mimic this in a metal alloy.

The question was, he says, "Can we design a material with a microstructure that makes it most difficult for cracks to propagate, even if they nucleate?" Bone provided a clue to how to do that, through its hierarchical microstructure - that is, the way its internal structures have different patterns of voids and connections at many different length scales, with a lattice-like internal structure - that combines strength with light weight.

The team developed a kind of steel that has three key characteristics, which combine to limit the spread of cracks that do form. Besides having a layered structure that tends to keep cracks from spreading beyond the layers where they start, the material has microstructural phases with different degrees of hardness, which complement each other, so when a crack starts to form, "every time it wants to propagate further, it needs to follow an energy-intensive path," and the result is a great reduction in such spreading.

Also, the material has a metastable composition; tiny areas within it are poised between different stable states, some more flexible than others, and their phase transitions can help absorb the energy of spreading cracks and even lead the cracks to close back up.

To further understand the relative roles of these three characteristics, the team compared steels each with a combination of two out of the three key properties. None of these worked as well as the three-way combination, he says. "This showed us that our modification has better fatigue resistance than any of these."

The testing of such materials under realistic conditions is difficult to do, Tasan explains, partly because of "the extreme sensitivity of these materials to surface defects. If you scratch it, it's going to fail much faster." So meticulous preparation and inspection of test samples is essential.

This finding is just a first step, Tasan says, and it remains to be seen what would be needed to scale up the material to quantities that could be commercialized, and what applications would benefit most.

"Economics always comes into it," he says. "I'm a metallurgist, and this is a new material that has interesting properties. Large industries such as automotive or aerospace are very careful about making changes in materials, as it brings extra effort and costs."

But there are likely to be several uses where the material would be a significant advantage. "For critical applications, [the benefits] are so critical that change is worth the extra trouble" about the cost, he says. "This is an alloy that would be more expensive than a basic low-carbon steel, but the property benefits have been shown to be quite exceptional, and it's with much lower amounts of alloying metals (and hence, costs) than other proposed materials."

Research paper

Understanding what's happening inside liquid droplets
Atlanta GA (SPX) Mar 09, 2017
For most people, the drip, drip, drip of a leaking faucet would be an annoyance. But for Georgia Institute of Technology Ph.D. candidate Alexandros Fragkopoulos, what happens inside droplets is the stuff of serious science. In the laboratory of Alberto Fernandez-Nieves in Georgia Tech's School of Physics, Fragkopoulos is studying how toroidal droplets - which initially take the shape of a donut ... read more

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

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

Comment on this article using your Disqus, Facebook, Google or Twitter login.

Share this article via these popular social media networks DiggDigg RedditReddit GoogleGoogle

NASA Releases Free Software Catalog

India has capability to develop space station, says top official

Orion spacecraft achieves key safety milestone

The NASA Imager Dentists Use Daily

Europe launches fourth Earth monitoring satellite

Elon Musk: tech dreamer reaching for sun, moon and stars

ULA launches NROL-79 payload for NRO

SpaceX says it will fly civilians to the moon next year

New evidence for a water-rich history on Mars

Humans May Quickly Evolve on Mars, Biologist Claims

NASA Orbiter Steers Clear of Mars Moon Phobos

Remnants of a mega-flood on Mars

Riding an asteroid: China's next space goal

China to launch space station core module in 2018

China's 1st cargo spacecraft to make three rendezvous with Tiangong-2

Thinking Big: China Hopes to Conduct 2nd Mission to Mars by 2030

Iridium Safety Voice Communications Installs Surge Past 500 Aircraft

OneWeb, Intelsat merge to advance satellite internet

Turkey Moves Closer to Launching Own Space Agency

GomSpace to supply satellites for Sky and Space Global constellation

Understanding what's happening inside liquid droplets

3-D printing with plants

Researchers remotely control sequence in which 2-D sheets fold into 3-D structures

Bubble-recoil could be used to cool microchips, even in space

Hunting for giant planet analogs in our own backyard

Faraway Planet Systems Are Shaped Like the Solar System

Biochemical 'fossil' shows how life may have emerged without phosphate

The missing link in how planets form

Juno to remain in current orbit at Jupiter

Europa Flyby Mission Moves into Design Phase

NASA receives science report on Europa lander concept

New Horizons Refines Course for Next Flyby

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