[Homeroast] Poisson's ratio WAS: Re: Compak vs Macap vs Rocky Grinders

Mike Koenig koenig.mike at gmail.com
Tue May 18 09:34:03 CDT 2010


I'm probably splitting hairs here, but Poisson's effect happens on the
molecular level, with bonds elongating under pressure or strain.  I'm not a
geoscience guy, but I imagine the effect effect would happen in rocks, dense
clays and shale, etc,  but what you are seeing in a coffee puck is
interactions between discrete non-uniform particles.

I'm not arguing at all that you don't get some lateral expansion during
tamping, since that certainly does happen, but it's not necessarily uniform,
and dependent on the distribution (and re-arrangement under force) of the
particles, as opposed to poisson's effect, which describes a predictable
amount of lateral expansion based on the change axial length.  If the
expansion was due to poisson's effect, the puck would spring back when you
let go of the tamper.   What you are getting is some re-arrangement of the
particles under force (like when you step in sand, and it moves out of the
way under your foot).

--mike



On Tue, May 18, 2010 at 3:01 AM, <raymanowen at gmail.com> wrote:

> Then I don't know why the grounds would press out and seal against the
> sides
> of the basket when you are only applying axial force with the tamper.
> Hydrostatic?
>
> I hope I don't owe a refund of all our pay at the Geophysics Research
> Institute at CSM. Please don't tell Dr. Levent Ozdemir or Dr. Russ Miller
> we
> were doing bad oil shale research. Damn!
>
> What supports you when you walk on a sandy beach?
>
> Teach me, please. -ro
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