Stronger, Lighter, Cheaper

Written by Catherine Bolgar*
NanomaterialIndustrial materials involve trade-offs. Desirable qualities tend to come with undesirable flip sides. Strength, for example, tends to come at the expense of ductility, or the ability to stretch without breaking. So the stronger something is, the more it’s likely—ironically—that when it does fail, it fails completely.

What if you could have both high strength and ductility? This is likely to happen, thanks to breakthroughs in new materials, many of which involve building the materials in innovative ways at the atomic level.

A microscopic view of metals would show them as made up of grains. Stronger materials have smaller grains, and more ductile materials have larger grains, explains Yuntian Zhu, professor of materials science and engineering at North Carolina State University in the U.S. However, if you make an entire part with small grains for high strength, it might fail catastrophically under stress.

When you make any structure, you want at least 5% ductility. The more ductility, the safer it is. But the downside is that the strength comes down,” he says.

Dr. Zhu found that by forming steel with larger grains inside and gradually moving to smaller grains at the surface, the result has both strength and ductility. This gradient structure is found in nature, he says, for example in plants and bones.

Near the surface, it’s harder. As you go deeper it gets softer,” Dr. Zhu says. “Nature just puts raw materials where they’re needed most. It minimizes the material cost. In nature, that proves useful.”

Using a gradient structure in steel could extend the lives of bridges, ships and oil pipelines, for instance.

Hardening steel by working it is another technique to make steel that’s both strong and ductile. Twinning-induced plasticity—or TWIP—steel is strengthened by twisting, deforming, bending, flattening or hammering it. At Brown University, researchers twisted cylinders of TWIP steel to deform the molecules on the surface. The molecules in the center remained unaffected, providing the flexibility, while the surface got harder, providing more strength.

Usually when something is strong, it’s also heavy. What if you could have both strength and lightness?

Nicholas X. Fang, associate professor of mechanical engineering at the Massachusetts Institute of Technology, has developed a foam material that can withstand a weight 10,000 times greater than its own.

“It’s as light as aerogel, yet as stiff as a hammer,” he says. Much of the space between the structures is void, which is why the material is so light.

The material uses nanotubes or nanowires a quarter of the size of a human hair to form a network or structure that takes away the load. “Each of the nanotubes under the load are under compression or a stress state,” Dr. Fang says. “But they turn out to be quite resilient. In the lab, we compress the samples to 60% of their original size.”

Dr. Fang is contemplating applications for this new material. The material could absorb impact while reducing weight, for example, in a tennis racket that’s lighter than aluminum alloy, yet able to deliver similar strength against a bouncing ball.

It could be important for microstructures in batteries,” he adds. Batteries receive a lot of shock when charging, which causes the structure to suddenly expand—and corrode. “If we could use this material in a battery, we could solve the challenge of quick charging,” he says.

Satellites also could benefit from a material that’s very lightweight, to reduce the payload, yet able to withstand shocks.

Nanowires in three-dimensional structures also are being explored by researchers at the University of California, Davis. By combining atoms of semiconductor materials—such as gallium arsenide, gallium nitride or indium phosphide—into nanowires that form structures on top of silicon surfaces, they hope to create a new generation of fast electronic and photonic devices.

The nanowire transistors could be used to make sensors that can withstand high temperatures and are easier to cool.

polymer surfaceSomething everybody wants to be strong yet shatterproof is their smartphone screen. Researchers at the University of Akron in Ohio have come up with a transparent layer of electrodes on a polymer surface that could stand up to repeatedly having adhesive tape peeled off and retain its shape after being bent a thousand times. The new film may be cheaper to make than the coatings of indium tin oxide now used on smartphone screens.

In fact, in a number of cases, the materials or processes themselves aren’t necessarily expensive, which makes them likely to be adopted relatively quickly.

It’s actually quite easy,” says Dr. Zhu about making steel with a gradient structure. “The only thing is, can we do it in an industrial way or develop a technology to do it?” The cost is likely to be very low, and some in industry already are trying it.

“It might take a few years for widespread adoption,” he says.

The super-strong foam material developed by Dr. Fang isn’t expensive, but the manufacturing process is—at least for now. Only a few centimeters of the material can be made, which is a limitation of the printing process, not the material itself, Dr. Fang says. “Now it’s important to connect the dots to make it into a larger format at lower cost.”

*For more from Catherine, contributors from the Economist Intelligence Unit along with industry experts, join The Future Realities discussion.

Catherine

Catherine

Catherine Bolgar is a former managing editor of The Wall Street Journal Europe, now working as a freelance writer and editor with WSJ. Custom Studios in EMEA. For more from Catherine Bolgar, along with other industry experts, join the Future Realities discussion on LinkedIn.
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