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Folding bowls for dogs, flexible medical tubes and drinking straws all seem to work on a common principle, breaking down in a variety of mechanically stable and useful states. Despite the many applications of such "designer material" structures, however, the fundamental mechanisms of their operation have so far remained mysterious, according to materials scientists at the University of Massachusetts, Amherst, directed by Ryan Hayward.
Now he and his colleagues, including Hayward's first author and former Ph.D. student, Nakul Bende, and their fellow physicist theorist at UMass Amherst, Christian Santangelo, along with mechanic James Hanna and students at Virginia Tech, report that he and his colleagues, they have discovered how these "multi-stable" structures composed of the stacked conical sections are subjected to an accumulated tension of prestressing "because the material is forced into a closed ring which is more curved than it naturally desires. "says Hayward.
"What we have discovered is that the very useful property of being mechanically stable in a curved configuration seems to require prestressing.As far as we know, no one had ever looked at how and why these structures had a curved state stability, "he adds.
"It will be helpful for us to understand this fundamental principle, which is essential for designing new applications. If you want to build a reconfigurable device, it's important to know why it works and when it may fail. "The details appear in the current online number of Soft matter.
Hayward argues that the mechanisms behind the ability of corrugated tubes to be lengthened and shrink are "fairly well established", as is the idea that moving materials between mechanically stable states requires overcoming an energy barrier. By playing with a variety of colorful flexible tubes on his desk, he demonstrates that the tube retains its shape in either state and that a barrier of energy is crossed when it appears.
"The mystery is why this tube of stacked cones should be stable in a bent state," he notes. "There is no obvious reason why a curved straw should want to be stable when it is curved."
To experience this, he and his colleagues cut a tube lengthwise to see what would happen. Cutting the tube, he said, "we realized that the tube would open and flatten, which was an unexpected moment, it was something we had to go back and try to understand. The key to discovering the role of We found that when we relax the curvature, the lack of stored energy eliminates stability in the curved state.We also built tubes that we forced to close to a smaller radius, in order to introduce prestressing, and found that it restored the hold a curved shape.
They analyzed this effect of "prestressing" by analyzing the curvature during deformation with X-ray tomography and a simple mechanical model to capture the qualitative behavior of highly reconfigurable systems.
The authors point out that "many biological mechanisms exploiting instantaneous transitions between mechanically stable states of slender and mechanically stable elastic structures allow for rapid movement. Although much of the literature has focused on bistability, systems supporting multiple stable states attract the design of highly reconfigurable structures, such as those to which they report.
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Material provided by University of Massachusetts at Amherst. Note: Content can be changed for style and length.
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