Re: [ATM] Break Strength of Glass

[Jan Bentz <jbentz@inreach.com>]

 Bob--The breaking strength will depend almost entirely on scratches, 
visible or not and other defects.  The quality of polish, particularly 
around the edge,determines to at least a factor of 10 the breaking 
strength of glass.  If the required vacuum  applies over roughly 
1000lbs/sq in tension then you should think of flame polishing the edge.

Jan Bentz

Bob Walker wrote:

>Here's one for all of you structural engineers out there.  I'm thinking of
>vacuum flexing a large, thin mirror just for the heck of it.  I did a PLOP
>analysis and figured that with a 36" x 3/8" disc of plate glass, about 5 psi
>of vacuum would produce about 5 1/5 mm of sag (and sagitta, too), resulting
>in an f/10 mirror.  Probably nothing but an ant-burner, but what else am I
>going to do with 3/8" glass?  The question, which has resisted all my
>efforts to research it via Google, is: can such a piece of glass bend that
>much without breaking?  When I built my bridge, I had no trouble finding
>tables and equations for beam strength of any species of wood you care to
>name, but no dice for glass. As I recall, even Schmidt himself broke a plate
>or two with his vacuum pan, but still I'd rather not.
>
> *  Best regards, Bob
>*
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