| Heat-treated glasses are classified as either fully tempered or heat strengthened. According to Federal Specification DD-G-1403B, fully tempered glass must have a surface compression of 10, 000 psi or more or an edge compression of 9, 700 psi or more. Heat-strength glass must have a surface compression between 3, 500 and 10, 000 psi, or an edge compression between 5, 500 and 9, 700 psi. The fracture characteristics of heat- strengthened glass vary widely from very much like annealed glass near the 3, 500 psi level to similar to fully tempered glass at the 10, 000 psi level. |
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