Why silos burst

Force chain

Believe it or not, grain silos are interesting structures. They’ve been known to explode without warning, which is hard to explain since they are filled with, well, grain.

But grain turns out to be kinda interesting too. In recent years, researchers have begun to get a handle on some of the strange and counterintuitive ways in which grain behaves as it flows and as it is placed under pressure.

One of the most interesting developments has been the discovery of “force chains”, networks of particles that form as the force is passed from one grain to the next (see picture). In this way, forces of many orders of magnitude greater than expected can be transmitted through the medium.

John Wambaugh and colleagues at Duke University in Durham have been studying the force networks that are set up within a two-dimensional silo and how these can make the forces behave in an extraordinary, non-linear way.

When grain is added to the top of the silo, the pressure in the medium increases but goes on increasing in a non-linear way even after the addition of material has stopped before decaying, a so-called “giant overshoot” effect.

How to explain this? Usually, force chains break and reform as the pressure changes in a granular medium and this helps to spread the forces evenly within it.

But Wambaugh thinks the non-linear behaviour suggests that something else is going on. He says that in certain circumstances, the force chains become locked in place and so that the additional pressure spreads much further and deeper than usual, creating the giant overshoot.

It might also explain why silos sometimes burst unexpectedly.

Ref: arxiv.org/abs/0801.3387: Force Networks and Elasticity in Granular Silos

2 Responses to “Why silos burst”

  1. Zephir says:

    Grain silos structures are emergent structures, similar to dark matter streaks and foamy density fluctuations, which are forming inside of dense particle systems, i.e. by the same way, like the strings of string theory (compare the free fermion models of ST).

    http://superstruny.aspweb.cz/images/fyzika/aether/foam_part.gif
    http://www.chem.leeds.ac.uk/People/CMR/criticalpics.html

    Being formed by very dense grainy systems, where the energy spreading & cumulation proceeds very slowly, they’re sharing certain common properties with vacuum phase transforms, like these explosions “without warning”.

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