8.9 - strain points is commonly considered the annealing...

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Softening point – 10 7.6 poises. At this temperature the glass will flow at an appreciable rate under its own weight. Annealing point – 10 13.4 poises. Internal stresses can be relieved in about 15 minutes at this temperature. This is roughly T g . (The annealing range is 10 12.5 to 10 13.5 ) Strain point – 10 14.5 poises. Below this temperature the glass is rigid and stress relaxation occurs only at a slow rate. In other words, there is little plastic deformation before failure. The interval between the annealing and
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Unformatted text preview: strain points is commonly considered the annealing range of a glass. A hard glass has a high softening point A soft glass has a low softening point. A long glass has a large temperature difference between its softening and strain points. Above T g , viscosity follows an Arrhenius form: η = η o e +Q/RT where Q is the molar activation energy for viscous flow. (The sign on the exponent would be negative if we considered fluidity instead of η )...
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This note was uploaded on 08/10/2009 for the course ENGN 45 taught by Professor Wendy during the Spring '09 term at City College of San Francisco.

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