[ATM] Re: RTV, You Will Comply

[jonah at eecs.berkeley.edu (Jeff Anderson-Lee)]

Thanks Stuart.  I think this is much less than the PSI estimate of 
89900psi from the other day.

F = EA(dh)/H  or E = FH/A(dh)

(7.2 lb) *  (0.125 in)  / (0.82^2/4/pi in^2) / 0.004 in  = 427 lb/in^2 
27131.14


That makes a *big* difference on the viability of RTV on a stiff plate 
backing.  I'm a little tired tonight, so perhaps another time.

Jeff

Stuart Hutchins wrote:

>Concerning the compliance of RTV blobs used in a mirror cell, here are the
>measurements taken on my sample, a "typical RTV pad".  These measurements
>give a way to calculate the force transmitted to the mirror by thermal
>expansion, warping or other movement of the mirror cell if the mirror is
>glued to it with a set of similar pads.
>
>The test unit is a single RTV pad between two 1 inch square aluminum plates,
>1/8 inch thick.  The plates were spaced apart by a short 1/8 inch diameter
>rod across each corner while the RTV blob cured.  The average diameter of
>the pad is .82 inches, and the thickness .125 inch.
>
>Measurement of deflection under compression:  reasonably linear, average
>spring constant is
>1791 lb/inch.
>     LOAD(lbs)       DEFLECTION(inches)
>        2.0                      .001
>        3.75                    .002
>        5.4                      .003
>        7.2                      .004
>
>Measurement of sideways deflection under shear load.  Linear within
>measurement error.  Average shear spring constant is 142 lbs/inch.
>     SHEAR LOAD(lbs)        DEFLECTION(inches)
>        1.0                                .006
>        2.0                                .012
>        3.0                                .022
>        4.0                                .028
>
>Hopefully this may be of some use to those who are designing/modeling glued
>mirror cell systems.
>
>Stuart Hutchins
>
>
>  
>