How granular material becomes solid: Stress causes clogs in coffee and coal
It's easy to get in a jam. But it's much harder to explain exactly how or when it started.
Scientists still aren't sure what causes clogs in flowing macroscopic
particles, like corn, coffee beans and coal chunks. But new experiments
by Duke physicist Robert Behringer and his colleagues suggest that when
particles undergo
a force called shear strain, they jam sooner than expected.
The results appear in the Dec. 15 issue of Nature. Shear strain is sort
of like cupping sand between your hands, and then, without changing the
width between them, moving one hand forward and the other hand
backward, Behringer said. Not much sand flows between your hands with a
force like this. Many flows, including those of nuts, coffee and coal,
inherently produce this type of movement among grains, but the design
and engineering for hoppers and other dispensers that don't account for
it won't work well, Behringer said.
The new work "points out
the deficiencies in our current theoretical framework for when granular
materials jam," said Corey O'Hern, an expert in granular media at Yale
University who was not involved in the new study. A deeper understanding
of this point will lead to the design of new composite granular matter
and also to the development of advanced materials that could counter
weapons of mass destruction, including amplifiers and other
countermeasures for deflecting blast waves, he said.
Read more at: http://phys.org/news/
Image: Photoelastic grains under shear. Photo: Behringer Group, Duke University
How granular material becomes solid: Stress causes clogs in coffee and coal
It's easy to get in a jam. But it's much harder to explain exactly how or when it started.
Scientists still aren't sure what causes clogs in flowing macroscopic particles, like corn, coffee beans and coal chunks. But new experiments by Duke physicist Robert Behringer and his colleagues suggest that when particles undergo
It's easy to get in a jam. But it's much harder to explain exactly how or when it started.
Scientists still aren't sure what causes clogs in flowing macroscopic particles, like corn, coffee beans and coal chunks. But new experiments by Duke physicist Robert Behringer and his colleagues suggest that when particles undergo
a force called shear strain, they jam sooner than expected.
The results appear in the Dec. 15 issue of Nature. Shear strain is sort of like cupping sand between your hands, and then, without changing the width between them, moving one hand forward and the other hand backward, Behringer said. Not much sand flows between your hands with a force like this. Many flows, including those of nuts, coffee and coal, inherently produce this type of movement among grains, but the design and engineering for hoppers and other dispensers that don't account for it won't work well, Behringer said.
The new work "points out the deficiencies in our current theoretical framework for when granular materials jam," said Corey O'Hern, an expert in granular media at Yale University who was not involved in the new study. A deeper understanding of this point will lead to the design of new composite granular matter and also to the development of advanced materials that could counter weapons of mass destruction, including amplifiers and other countermeasures for deflecting blast waves, he said.
Read more at: http://phys.org/news/
Image: Photoelastic grains under shear. Photo: Behringer Group, Duke University
The results appear in the Dec. 15 issue of Nature. Shear strain is sort of like cupping sand between your hands, and then, without changing the width between them, moving one hand forward and the other hand backward, Behringer said. Not much sand flows between your hands with a force like this. Many flows, including those of nuts, coffee and coal, inherently produce this type of movement among grains, but the design and engineering for hoppers and other dispensers that don't account for it won't work well, Behringer said.
The new work "points out the deficiencies in our current theoretical framework for when granular materials jam," said Corey O'Hern, an expert in granular media at Yale University who was not involved in the new study. A deeper understanding of this point will lead to the design of new composite granular matter and also to the development of advanced materials that could counter weapons of mass destruction, including amplifiers and other countermeasures for deflecting blast waves, he said.
Read more at: http://phys.org/news/
Image: Photoelastic grains under shear. Photo: Behringer Group, Duke University
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