1979 Volume 87 Issue 1011 Pages 571-575
Photoelastic constants (hereafter called as B) of SiO2 glass, 5Na2O⋅95GeO2 glass, Ca(PO3)2 glass, soda-lime glass and Pyrex glass were measured. Weyl's theory on B of glass cannot explain why B of SiO2 is 1.33 times larger than B of soda-lime glass.
The structure of SiO2 glass which consists of nonplanar rings of 6 SiO4 tetrahedra has the vacant space within the rings.
The compressive stress which changes the bond angle at the corner oxygen causes the vacant space to decrease toward the parallel direction of the applied stress. This deformamtion contributes to the increase of B.
In GeO2 and 5 Na2O⋅95GeO2 glasses, the same phenomena occur.
Therefore, B of these glasses is large.
The structures of borate and borosilicate glasses consist of tetraborate group and diborate group both with vacant space.
The compressive stress decreases the vacant space and thus increases the B value.
The structures of Ca(PO3)2 and soda-lime glasses have no vacant space and thus the proposed mechanism cannot work.
Therefore, B of these glasses is small.
