[ATM] RTV, You Will Comply

[stuart452 at earthlink.net (Stuart Hutchins)]

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