A new method is developed for determining of retardations and azimuth angles in two-ply retarder. This method is based on Senarmont's compensator. But linearly, circularly and elliptic polarized light and two monochromatic lights are used in this method. It is discussed in detail by the Stokes'parameter how a state of incident polarized light is transformed by the two-ply retarder on the Poincare sphere. Each azimuth angle and retardation can be measured without separating the test piece into each retarder. Good agreements are obtained between experimental and theoretical values.

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Stokes parameters (S₁, S₂, S₃) of monochromatic light can be measured by adjustable quarter-wave plate and linear polarizer (AQP method). In the Stokes parameters measurement of the light at an arbitrary wavelength over a wide wavelength range, S₃ by the AQP method is affected by the phase difference error Δρ_i of the quarter-wave plate mismatch and the Stokes parameter S₂. S₃ by a JCAQP method developed the AQP method is calculated by considering only Δρ_i. In this paper, JCAQP method was proved visually on Poincare sphere and was discussed.

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A mechanism of form optical activity in inhomogeneous non-absorbing and absorbing objects is investigated on the basis of coupled-mode equations. It is considered how to represent the effect of form optical activity and natural optical activity in the medium on the state of polarized light passing through it. This can be treated as a problem representing the optical property of a small interval on a light path in the medium by a combination of optical elements, such as a retarder, a rotator and a partial polarizer.

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An improved phase-shift method called a generalized one is used for automatically measuring the principal-stress directions in the whole field of a model. This method uses light intensity values obtained with the rotation of the polaroids in a dark-field plane polariscope at each point. In order to investigate the accuracy of the measurement, light intensity curves in time series with different noise, ΔI, different numbers of data which constitute the curves, n, and different fringe orders, N, and principal-stress directions, φ, at measured points are used in computer simulation. The magnitude and sign of noise are determined within the range of ±1% to ±20% of the light intensity at a point using random numbers. As a result, the accuracy of the principal-stress directions obtained by the method is not affected very much by noise for the number of data more than 50. The errors, |ΔΦ|, for N=0.1, 0.25 and 0.5 are 0.886, 0.290 and 0.221deg for n=100 and ΔI_max=±15%, respectively. Furthermore, the method is applied to the experimental images obtained from a circular disk subjected to a diametrically compressive load in a dark-field plane polariscope with a white lamp. The result is in good agreement with the theory except for region near the zero-and first-order fringes.

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A new method is presented for obtaining directly the elastic stress and moment at a point in a thin, frozen stress isotropic plate. The stress and moment were obtained by use of modified cone method and subslice methods, involving measurement of the relation between fringe order and azimuth angle of extract pieces under immersion state. The experimental results show good agreement with the theory of elasticity.

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The stress concentration factors on the edges of square plates with rounded square holes and the stress intensity factors for the corner edge cracks of square plates with square holes are evaluated by photoelastic experiment. The epoxy resin models of hollow square plates are fitted into a pantograph frame, and the models are loaded by tensile loads in the diagonal direction of the frame.
Numbers of the isochromatic fringe patterns taken by means of a CCD camera are recorded in a magneto optical disk, and transformed into the thinning images of them by utilizing an image processing analyzer. From the thinning images obtained, the required data are collected to evaluate the stress concentration factors and the stress intensity factors.
The local stress concentration factors are shown in the diagrams for the local muximum stress at the some points on the inner and outer edges of the hollow square plate, and finally a diagram of the stress concentration factor depended on the radius of curvature of the corners and the wall thickness are obtained from their local stress concentration factors. Moreover, and the stress intensity factors for the corner edge cracks are given as diagrams representing the behavior depended on the crack depth and the wall thickness.

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The temperature dependence of the mechanical and physical properties of heated plastic materials have been examined by several material tests. The materials used are epoxy resin, acrylic resin and polycarbonates. For instance, the mechanical properties such as Young's modulus and Poisson's ratio etc. have been examined. And the physical properties such as the thermal conductivity etc. have been examined, too.
Also, the optical constants in the caustic method are of great importance in the case of the calculation of stress intensity factor. Therefore, the temperature dependence of optical constants was particularly examined by the tension test using thermostatic oven. Some cases of stress intensity factor with regard to the temperature have been calculated. Our experimental results are as follows.
1) The values of the mechanical properties such as Young's modulus varying with the change of temperature have been obtained.
2) The values of the optical constants and photoelastic sensitivity for the variation of temperature have been obtained, too.

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The automatic retardation tester was made to measure easily and precisely the absolute retardation in the polymar films. The retardaion in the test piece can be measured for all visible light, because the tester has the composite quater wave plate in it's optical system.
In the present study, this equipment is applied for the stress analysis in the photoelastic model. The photographs has been used as the most popular method of stress analysis in the photoelasticity. Its method, it is difficult to determine the absolute fringe order in the isochromatics fringe pattern. Moreover it is also difficult to determine precisely the direction of the principal stress in each point of the test piece. The error is included in each measured value in the photograph's method. The validity of the tester for stress analysis is confirmed by comparing the results of stress analysis of photograph's and tester's method.

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