Abstract

The photo-elastic coefficients of rock-salt, sylvite and fluorite were measured for the mercury lines 436, 546, and 578 μμ by means of a modified Soleil-Babinet compensator. Compared with glass the coefficient was positive for rock salt, negative for sylvite, positive for fluorite stressed normal to a cube face and negative for fluorite stressed normal to an octahedral face. For all cases, except that of fluorite stressed normal to octahedral faces, relative retardation (Δ) plotted against stress per cm²(f) gave a straight line for loads between 10 000 and 20 000 gg; this line extended cut the axis of Δ above zero. Therefore for cubic crystals the relation between photo-elastic effects and externally applied force is not the simple direct relation assumed for noncrystalline materials.

© 1927 Optical Society of America

Photo-elastic Investigations of the Tensil Test Specimen, the Notched Bar, the Ship Propeller Strut, and the Roller Path Ring*

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