The Secret Strength of Gnashing Teeth
martyb writes:
The Secret Strength of Gnashing Teeth:
The strength of teeth is told on the scale of millimeters. Porcelain smiles are kind of like ceramics-except that while china plates shatter when smashed against each other, our teeth don't, and it's because they are full of defects.
Those defects are what inspired the latest paper led by Susanta Ghosh, assistant professor in the Department of Mechanical Engineering-Engineering Mechanics. The research came out recently in the journal Mechanics of Materials. Along with a team of dedicated graduate students-Upendra Yadav, Mark Coldren and Praveen Bulusu-and fellow mechanical engineer Trisha Sain, Ghosh examined what's called the microarchitecture of brittle materials like glass and ceramics.
"Since the time of alchemists people have tried to create new materials," Ghosh said. "What they did was at the chemical level and we work at the microscale. Changing the geometries-the microarchitecture-of a material is a new paradigm and opens up many new possibilities because we're working with well-known materials."
[...] Stronger glass brings us back to teeth-and seashells. On the micro level, the primary hard and brittle components of teeth and shells have weak interfaces or defects. These interfaces are filled with soft polymers. As teeth gnash and shells bump, the soft spots cushion the hard plates, letting them slide past one another. Under further deformation, they get interlocked like hook-and-loop fasteners or Velcro, thus carrying huge loads. But while chewing, no one would be able to see the shape of a tooth change with the naked eye. The shifting microarchitecture happens on the scale of microns, and its interlocking structure rebounds until a sticky caramel or rogue popcorn kernel pushes the sliding plates to the breaking point.
That breaking point is what Ghosh studies. Researchers in the field have found in experiments that adding small defects to glass can increase the strength of the material 200 times over. That means that the soft defects slow down the failure, guiding the propagation of cracks, and increases the energy absorption in the brittle material.
"The failure process is irreversible and complicated because the architectures that trap the crack through a predetermined path can be curved and complex," Ghosh said. "The models we work with try to describe fracture propagation and the contact mechanics at the interface between two hard-brittle building blocks."
Better to bend than break.
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