Текст B. Toughened glass is about five times stronger in bending than ordinary annealed glass because the surface of the glass is prestressed in compression

TOUGHENED GLASS

Toughened glass is about five times stronger in bending than ordinary annealed glass because the surface of the glass is prestressed in compression. No tensile stresses will take place on the surface if the stress that is applied is not greater than this prestress. In order to make toughened glass its surface, when it is at a high temperature, is rapidly cooled. This process not only produces compression on the surface but tension in the middle of the toughened glass and this accounts for the characteristic way toughened glass shatters into pieces when broken. This is a relatively safe way when a failure takes place. The greater safety of toughened glass over annealed glass is an important reason for its selection. Because toughened glass has a significant tensile strength, it is able to accept not only the applied stress due to loads but also stresses due to temperature difference. In this way it can take thermal shocks and not crack. Disadvantages of toughened glass are its loss of properties above about 300°C (575°F) and the fact that it may not be drilled, cut or shaped after toughening has been finished. Toughened glass has been widely used in buildings. High glass wall elevations have been constructed with the use of toughened glass. In this case the glass wall is hung from supports to avoid buckling.

Notes:

cool v. охлаждать(ся)

safe adj. безопасный

shatter v. разбиваться

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1. How strong is toughened glass?

2. Why is it so strong?

3. How is toughened glass made?

4. What is an important reason for its selection?

5. Why does toughened glass not crack due to temperature dif­ferences?

6. What are the disadvantages of toughened glass?

7. Where is toughened glass used in buildings?