ASU research points way to designing crack-resistant metals


June 24, 2015

Sometimes looking at something at the smallest scale can lead to solutions to big problems.

A recent study into the interactions of metal alloys at the nanometer and atomic scales is likely to aid advances in preventing the failure of systems critical to public and industrial infrastructure. cracking in gold alloy The image shows corrosion of a silver-gold alloy spontaneously resulting in the formation of nanoscale porous structures that undergo high-speed cracking under the action of a tensile stress. It helps demonstrate a discovery by an Arizona State University research team about the stress-corrosion behavior of metals that threatens the mechanical integrity of engineered components and structures. Download Full Image

Research led by Arizona State University materials science and engineering professor Karl Sieradzki is uncovering new knowledge about the causes of stress-corrosion cracking in alloys used in pipelines for transporting water, natural gas and fossil fuels – as well as for components used in nuclear-power-generating stations and the framework of aircraft.

Sieradzki is on the faculty of the School for Engineering of Matter, Transport and Energy, one of ASU’s Ira A. Fulton Schools of Engineering.

His research team’s findings are detailed in an advance online publication June 22 of the paper “Potential-dependent dynamic fracture of nanoporous gold” on the website of the journal Nature Materials.

Using advanced tools for ultra-high-speed photography and digital image correlation, the team has been able to closely observe the events triggering the origination of stress-corrosion fracture in a model silver-gold alloy and to track the speed at which cracking occurs.

They measured cracks moving at speeds of 200 meters per second corresponding to about half of the shear wave sound velocity in the material.

This is a remarkable result, Sieradzki said, given that typically only brittle materials such as glass will fracture in this manner and that gold alloys are among the most malleable metals.

In the absence of a corrosive environment, these gold alloys fail in the same manner as children’s modeling clay, Sieradzki explained: Roll modeling clay into a cylindrical shape and you can stretch it by about 100 percent before it slowly tears apart. In the presence of corrosive environments, silver is selectively dissolved from the alloy causing porosity to form (see photo). If this occurs while the alloy is stressed, the material fails as if it were made of glass.

These results provide a deeper understanding of the stress-corrosion behavior of such metals as aluminum alloys, brass and stainless steel that threatens the mechanical integrity of important engineered components and structures.

The team’s discoveries could provide a guide for “designing alloys with different microstructures so that the materials are resistant to this type of cracking,” Sieradzki said.

The research has been funded by the Department of Energy’s Basic Energy Science program.

His co-authors on the Nature Materials paper are former or current ASU materials science and engineering graduate students: Shaofeng Sun earned her doctoral degree in 2013; Xiying Chen is a third-year doctoral student; and Nilesh Badwe earned a doctoral degree earlier this year.

Joe Kullman

Science writer, Ira A. Fulton Schools of Engineering

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ASU works with Navajo planners to map out tribe's destiny through training program


June 24, 2015

The Navajo Nation is continuing to map its own future, and ASU is playing a key support role.

In 1998, the Navajo Nation passed the Local Government Act, which decentralized community planning for the Navajos and gave significant governing authority to the nation’s local jurisdictions, called chapters. However, the legislation came with its own set of problems. woman conducting training program Shea Lemar (center) conducts a community-planning training session for 16 members of the Navajo Nation on June 17 in Tempe. Photo by: Courtney Pedroza/ASU News Download Full Image

The Navajo Nation hired outside planners and consultants, but the results were not effective, possessed little creativity and the plans mostly sat on a shelf for years.

After conducting a two-year study, ASU’s School of Geographical Sciences and Urban Planning concluded that a new planning approach was needed. Furthermore, a training program was developed to provide the latest approaches and techniques for the tribal community's own regional plans.

That training is happening right now for the first time over a 12-day session at the Tempe campus, ending on June 26.

“We spent a lot of time and money on consultants, and they didn’t necessarily do very good work,” said Elerina Yazzie, one of 16 Navajo Nation planners participating in the training program. “To me, all they did was copy and paste their plans for every single chapter. They didn’t do the community work that was mandated, and they weren’t familiar with the land or people. It was a failure.”

David Pijawka, a professor of planning in the School of Geographical Sciences and Urban Planning and director of the Community Planning Training Program for the Navajo Nation, said the mistakes of the past can be corrected through proper guidance and use of the latest Geographic Information Systems and planning technologies.

“What we’re doing is bringing Navajo planners the decision-making tools they need to be effective and showing them the most advanced training possible,” Pijawka said. “Many people attending the program see the importance of what they’re doing here and will be going back to their chapters and transforming their communities. It’s groundbreaking.”

The coursework includes: Community-Based Planning in the Navajo Nation; Geographic Information Systems and Mapping; Tribal Legal Issues in Planning; Planning Methods; Land Use Issues, Grazing and Jurisdictions; Environmental Resources Assessment, Sustainable/Heritage Cultural Tourism and Social Entrepreneurship, and Transportation Planning.

Approximately 320,000 people identify themselves as Navajos, and the Navajo Nation covers land that is roughly the size of West Virginia.

Planner Faye Nez, who oversees 29 chapters near Gallup, New Mexico, said the training program has been invaluable and hopes that others will follow in her footsteps.

“Development means growth, and often that means getting a formal education,” Nez said. “It’s very hard to come from one culture and enter another. I know there are a lot of Navajo students with great minds, and they’re finally going to get organized training.”

For senior planner Louis Shepard, the program is an opportunity for dialogue and continued learning opportunities.

“I’m learning about methods and models that are currently being used and the planning environment, principles and applications,” Shepard said. “Hearing the different perspectives on the rural versus urban settings and how to address the needs of the people has been particularly helpful to me.”

Reporter , ASU Now

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