From: Aplanatic{at}aol.com
To: atm{at}shore.net
Reply-To: Aplanatic{at}aol.com


Hi Tom,

A few years ago I also needed to know the elastic modulus of RTV.  I was
interested in calculating the differential flexure between a guide scope
and a Schmidt camera for exposures of up to one hour.  One component of
this flexure is mirror tip due to compression/expansion of the RTV
attachment of the mirror to its cell.  Another component is shearing of
this attachment.

At the time I could not find the shear or bulk modulus of RTV, so I did an
experiment.  I attached a piece of glass to an aluminum base with a
controlled thickness of RTV.  Viewed through the glass, I then estimated
the area of RTV in contact with the glass.  By using a dial indicator to
measure displacement and weighting the glass with pieces of lead around the
edge, I was able to estimate the bulk modulus of the RTV at 170 PSI.  This
is just a ball-park estimate for clear GE Silicone II.

I'm sure that the test setup could be improved substantially; mine was
rather quick, dirty and probably not all that accurate.

Dave Rowe

Ton wrote:
> I seldom find mention of modulus of elasticity.
>
> Can I convert the above values to modulus of elasticity?  How?
>
> Thanks in advance,
> Tom Krajci
> Tashkent, Uzbekistan
>
>
>
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