Friday, August 13, 2010

Watching concrete crack: A new strength record



A small slab of a special concrete laced with short, twisted wires set a tensile strength record a few weeks ago in the civil engineering Structures Lab, the researchers involved say. Tensile strength is essentially resistance to stretching.

This stuff has about 100 times the stretchiness of conventional concrete. It can withstand 5,000 pounds per square inch after it starts cracking. It's the combination of strength and stretchiness that makes the material unique, the researchers say.

Postdoctoral researcher Kay Wille and professor emeritus Antoine Naaman invited me to watch one of their tests. They put a specimen of their concrete in a machine that pulls it apart until it fractures. I videotaped it. I was expecting something dramatic.

Turns out the drama was in what didn't happen. The material didn't break in half. It slowly cracked in scratches so tiny we could barely see them without a microscope. Wille first knew they were happening because he heard them.

There's more detail in the video. Naaman even offers to test anyone else's plate-like specimen purported to be stronger than theirs. (That buzz in the background is the natural din of the lab.)

Wille and Naaman are working on this new "ultra-high performance fiber reinforced material" with associate professor Gustavo Parra-Montesinos and professor Sherif Al Tawil.

Wednesday, August 4, 2010

A real-world test for a "fishy" clean energy technology

A device that works like a fish to harness clean, renewable energy from slow water currents was recently tested in the St. Clair River. This was the first real-world trial for VIVACE, which stands for Vortex Induced Vibrations for Aquatic Clean Energy. Here's some underwater video courtesy of Vortex Hydro Energy, the University of Michigan spin-out company that's commercializing it.



This is some seriously clever technology. Its shape and placement in the water set off "vortex induced vibration," a phenomenon that fish use to help them swim faster in a school. These are the same vibrations that, in wind, toppled the Tacoma Narrows bridge in 1940. Here's more detail on how it works and why it improves upon other hydrokinetic energy technologies.

On Aug. 2, researchers lowered a 10x11x15-foot, two-cylinder array 16 feet deep and 60 feet from shore at Port Huron. The converters ran for two hours.

“We’re very optimistic because it performed well," said Gus Simiao, CEO of Vortex Hydro Energy. "We did have one glitch with one of the subsystems, but it’s something that we can repair. We just have to spend some time redesigning it and testing it in the lab before we go back to the river.”

The team expects to be back at the river in May or June of 2011, when they plan to leave it there for prolonged testing over a couple of months.

Bernitsas is a professor in the Department of Naval Architecture and Marine Engineering.