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Novel laminated nanostructure gives steel bone-like resistance to fracturing under repeated stress

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.

Read more.

Earlier this fall, I attempted my first corn maze. It didn’t work out very well. Early on I unknowingly cut through an area meant to be impassable and thus ended up missing the majority of the maze. Soap, as it turns out, is a much better maze-solver, taking nary a false turn as it heads inexorably to the exit. The secret to soap’s maze-solving prowess is the Marangoni effect. 

Soap has a lower surface tension than the milk that makes up the maze, which causes an imbalance in the forces at the surface of the liquid. That imbalance causes a flow in the direction of higher surface tension; in other words, it tends to pull the soap molecules in the direction of the highest milk concentration. But that explains why the soap moves, not how it knows the right path to take. It turns out that there’s another factor at work. Balancing gravitational forces and surface tension forces shows that the soap tends to spread toward the path with the largest surface area ahead. That’s the maze exit, so Marangoni forces pull the soap right to the way out! (Video credit: F. Temprano-Coleto et al.)

In slow motion, vortex rings can be truly stunning. This video shows two bubble rings underwater as they interact with one another. Upon approach, the two low-pressure vortex cores link up in what’s known as vortex reconnection. Note how the vortex rings split and reconnect in two places – not one. According to Helmholtz’s second theorem a vortex cannot end in a fluid–it must form a closed path (or end at a boundary); that’s why both sides come apart and together this way. After reconnection, waves ripple back and forth along the distorted vortex ring; these are known as Kelvin waves. Some of those perturbations bring two sides of the enlarged vortex ring too close to one another, causing a second vortex reconnection, which pinches off a smaller vortex ring. (Image source: A. Lawrence; submitted by Kam-Yung Soh)

Note: As with many viral images, locating a true source for this video is difficult. So far the closest to an original source I’ve found is the Instagram post linked above. If you know the original source, please let me know so that I can update the credit accordingly. Thanks!

Yerres, Path Through the Old Growth Woods in the Park via Gustave Caillebotte

Size: 43x31 cm Medium: oil on canvas

How to Beam ➝ Noemi Makra Style

“I first ran for Congress in 1999, and I got beat. I just got whooped. I had been in the state legislature for a long time, I was in the minority party, I wasn’t getting a lot done, and I was away from my family and putting a lot of strain on Michelle. Then for me to run and lose that bad, I was thinking maybe this isn’t what I was cut out to do. I was forty years old, and I’d invested a lot of time and effort into something that didn’t seem to be working. But the thing that got me through that moment, and any other time that I’ve felt stuck, is to remind myself that it’s about the work. Because if you’re worrying about yourself—if you’re thinking: ‘Am I succeeding? Am I in the right position? Am I being appreciated?’ – then you’re going to end up feeling frustrated and stuck. But if you can keep it about the work, you’ll always have a path. There’s always something to be done.”

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