by Brooks Hays
Philadelphia (UPI) Sep 21, 2016
New research explains the deformation process of layered materials. Until now, scientists didn't have a solid grasp of how layered materials break down.
The new study, published this week in the journal Scientific Reports, shows the internal layers of layered materials -- whether a sedimentary rock outcropping or a sheet of graphite -- begin to buckle as they become stressed and deformed.
The findings are forcing scientists to rethink their models of metal deformation.
"Dislocation theory -- in which the operative deformation micromechanism is a defect known as a dislocation -- is very well established and has been spectacularly successful in our understanding the deformation of metals," Garritt J. Tucker, an assistant professor of material science and engineering at Drexel University, said in a news release. "But it never really accurately accounted for the rippling and kink band formation observed in most layered solids."
The internal kink bands, or ripple effect, observed by researchers in layered materials, is known as ripplocation.
Dislocation theory suggests a compressed metal can do one of two things, rebound to its original shape -- if it is elastic -- or become permanently dented. Ripplocation offers a third option: a return to its original shape while absorbing considerable energy.
This absorbed energy causes the rippling effect of deformation. Simulations prove the rippling occurs at scale. The same buckling seen within massive deformed rocks occurs at the atomic stage when layered graphite is compressed edge-on.
Scientists further examined the internal buckling process by imaging compressed ceramic layers.
"When we obtained high resolution transmission electron microscope images of the defects that formed as a result of the deformation we were not only able to show that they were not dislocations, but as importantly, they were also consistent with what ripplocations would look like," said Mitra Taheri, also an assistant professor of material science and engineering. "We now have evidence for a new defect in solids; in other words we have doubled the deformation micromechanisms known."
"There are many layered solids, in both nature and the built environment, that are technologically important, so it's essential to understand their behavior," concluded lead researcher Michel W. Barsoum, a distinguished professor at Drexel. "This new finding will require us to reexamine past findings and reinterpret results that to date were incorrectly explained using dislocation theory."
Space Technology News - Applications and Research
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