Strength of optical glass under conditions of axial compression

1. The strength of optical glass in uniaxial compression is one-third to one-half lower than the strength of high-strength technical glass, e. g., glass 13v, the sample variation coefficient is 50 to 100% larger, and therefore a higher safety factor is required in designing highly stressed components made of the given materials. 2. The strength of optical glass under axial compression, and also under loading of specimens by smooth metallic supports, depends to a considerable extent on the chemical composition, and in glasses containing lead oxide PbO2 it attains minimum values (800–1000 MPa). 3. The strength of prismatic specimens of optical glass and of pyroceram does not differ by more than 10% from the strength of cylindrical specimens, whereas the scatter of experimental data for the former is 1.25 to 1.35 times higher than for the latter. 4. The ratio of the mean level of rupture stresses in compression of optical glass by smooth metallic supports to their ultimate strength is correlated by a functional dependence with the ultimate strength in axial compression which in the first approximation may be approximated by a straight line. 5. Strength in axial compression, and also the upper and lower confidence limits with a confidence level α=95%, are not substantially affected by peculiarities of the production technology of cylindrical specimens under laboratory and industrial conditions as to the equal height of microunevennesses or by storage of specimens after production under normal conditions for three years or more.