The stresses in plane rotating discs with two eccentric holes located in symmetry with respect to the diameter of disc are investigated by means of photoelastic reflection and stroboscopic methods. The preliminary photoelastic experiment for rotating disc without eccentric holes is conducted in order to confirm the reliability of the experimental procedure in comparison with the known theoretical solution. The epoxy disc models with two eccentric circular holes of various radii or two eccentric rectangular holes with various radius of curvatures in the both ends are prepared. The results obtained for the tangential stresses on the boundaries of holes of rotating discs are shown in diagrams.

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Examination of quarter wave plate is carried out on the Poincare sphere for photoelastic experiments. The light intensity through an analyzer is given by coscos² ρ, where ρ is the half angle between a incident polarized light and the analyzer on the Poincare sphere. Using proper quarter wave plates, a test piece with a birefringence δ gives the light intensity of sinsin²δ /2 in the dark field. If quarter wave plates have same error Δ, its intensity is coscos²Δ ·sinsin²δ /2. And if each plate has different error, its intensity error becomes more large depending stress direction. In addition, optical alignments in which these plates have dichromatic and rotary power are also investigated on the Poincare sphere. Both cases give few error to experimental result with commercial plates. It is more easy to discuss light intensities of photoelastic of photoelastic fringes on the Poincare sphere.

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This paper describes a new method of finding the principal stress lines in a two-dimensional model by means of 5-8 rule as numerical integration by analytical theory of elasticity. The method is applied in detail to square and circular plates compressed by two diagonally opposite forces, and is found to be easy of operation and to yield results of good accuracy. In addtion, the determination of the special cases of 5-8 rule, and differential coefficient with arbitrary increaments is described in appendix.

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The steady thermal stresses produced in the hollow square plates with a circular hole or a square hole having rounded corners are investigated by means of photoelastic reflection method using high frequency induction heating apparatus already developed by authors. A lot of epoxy resin models of the hollow square plates are prepared. The radius of circular hole, radius of curvature in the corners of square hole and wall thickness are systematically varied.
The inner and outer boundaries of the models are kept constant temperature of 50°C and 0°C, respectively. The photoelastic experiment is conducted when the steady temperature distribution in the model was realized. The temperature distribution in the models and the thermal stresses on the inner boundary are obtained and summarized in several diagrams.

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Crystallographic conditions for photoelastical measurement of stresses induced in a silicon single crystal plate are made clear by numerical calculations. It is found that the coordinate system of the plate is specified depending on an incident light direction. Mechanical anisotropic properties of the plate are also calculated for the case where the plate has an elastically symmetrical axis in its plane. It is found that the variation of the mechanical anisotropy is small. Experiments on silicon cantilever in bending are performed by using an infrared photoelastic method. Experimental results show that the silicon single crystal plate can be used as a photo-anisotropic elastic material.

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A correction method of the relative retardation ρ and the angle φ of the principal stresses obtained in photoelasticity using Stokes parameter method is described. These errors are due to those of azimuth, ellipticity of the circular-polarized incident light and the phase difference of the quarter-wave plate used on the observing side. The Stokes parameter S3 in this method is obtained from both the intensities measured by the set of the circular polarizer and a rotated quarter-wave plate by 90°. The analysis using S₃ obtained in this method is in higher accuracy than the previous methods without the correction calculation, though the corrected value of ρ is obtained by approximation neglecting square term of error. The φ corrected is obtained without approximation. This method is also capable of applying to a different wavelength incident light.

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