51 



successive tints of passage, usually considered as the sharp distinction 

 between the erubescent and blue colors. 



The difference in wedge thickness for the number of divisions 

 corresponding to the compensator constant is one wave-length of white 

 light, 22. 7 X 10" inches. For an incremental change of load on the 

 specimen, the tint of passage moves along the compensator. The number 

 of divisions that the tint of passage moves on the compensator is the 

 figure used in the stress computations. 

 3. Advantages of a Birefringent Coating Analysis 



The technique of birefringent coating analysis is useful in deter- 

 mining: 



?i. The elastic or plastic strain distribution from static or dynamic 



loading. 



b. Instantaneous detection of stress concentration areas. 



c. Stress concentration factors around cracks, small holes, 

 fillets, and notches'^^^ 



d- Residual strains or stress from plastic deformations. 



e. True Yield strength. 



f . , Stresses in composite materials such as reinforced concrete. 



g.. Stresses in anisotropic materials such as wood. 



h- Stresses in and around the weld of dissimilar metals. 



i. Stresses in and around heterogeneous inclusions' '. 



Some of the special advantages of birefringent coating analysis are 



as follows: 



