[ATM] re: breaking strength of glass

["Ellen Mackenzie" <mackenzieconsulting@sympatico.ca>]

The Pilkington(PPG)web page has considerable engineering data for glass as
far as Young's Modulus, deflection formulas go. However, with the
availability of front surface mirror glass, why not start with a mirror? The
edges of your disc must be flawless. My reference work ( Theory and Design
of Pressure Vessels isbn 0-442-23184-9)adresses the deflection of circular
plates without the mention of hoop stress on the circumference. The hoop
stress on a glass plate must be considered since glass has such a poor notch
resistance.
I do wonder how you propose to reach the 30 foot focus of your instrument?


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