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Message ID: 124     Entry time: Mon May 13 14:49:35 2013
Author: Koji 
Type: Mechanics 
Category: Characterization 
Subject: Mounting Glass Bracket still broke with tightenin stress 

[Koji / Jeff]

This is the elog about the work on May 9th.

We made two glass brackets glue on the junk 2" mirrors with the UV glue a while ago when we used the UV bonding last time.

On May 7th:

We applied EP30-2 to the glass brackets and glued invar shims on them. These test pieces were left untouched for the night
and brought to Bob for heat curing at 94degC for two hours.

On May 9th:

We received the test pieces from Bob.

First, a DCPD mount was attached on one of the test pieces. The fasteners were screwed at the torque of 4 inch lb.
It looked very sturdy and Jeff applied lateral force to break it. It got broken at once side of the bracket.

We also attached the DCPD mount to the other piece. This time we heard cracking sound at 2 inch lb.
We found that the bracket got cracked at around the holes. As the glass is not directly stressed by the screws
we don't understand the mechanism of the failure.

After talking to PeterF and Dennis, we decided to continue to follow the original plan: glue the invar shims to the brackets.

We need to limit the fastening torque to 2 inch lb.

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