This paper elucidates the mechanism of formation of the data-curves and their properties. The curves are the loci of the unit polarization vector s (i, 0) plotted on the Poincaré sphere. The reason why a curve bends sharply under a certain condition is clarified, and an example of such phenomenon caused by the uniform rotation of the secondary principal stresses is described in detail.

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Fracture of blades or disks due to centrifugal force in rotary machines has often caused serious accidents. To optimize their dimensions and to ensure their safety in service, a practical study of the strength under centrifugal force is necessary.
In this paper, stress intensity factors were determined by using the photoelastic and caustics method. Stress intensity factors in a single crack are calculated as a function of the inclination crack of length 2a, the position at different velocities and at different values of the inclination crack angle φ and are measured in models of rotating disks using a photoelastic stress freezing method. The ratio (K_II/K_I) of the stress intensity factors determined by using the isochromatic fringe loops angle θ_m near the crack tip. The results of this experiment coincided favorably with the theoretical analysis results of Ishida and Terada (1).
Branched cracks are frequently encountered in the unstable fracture of various brittle materials. Stress intensity factors K_I and K_II were determined by using the photoelastic and caustics method, as a function of the branched crack of length ratio a_II/a_I and at different values of the branched crack angles 2θ at two velocities. The interaction in branched cracks was also discussed, together with a comparison of the results of these experimental methods.

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The thermal stress intensity factors for the crack on the outer edge of annulus under steadystate temperature distribution are evaluated by the photothermoelastic experiment. The photoelastic epoxy resin models of annuli with the various crack depth and wall thickness are prepared and installed in the vacuum chamber equipped in the experimental apparatus. The steady-atate temperature distribution of the annulus model under heating conditions of 5°C and 0°C on the inner and outer edges, respectively, is realized by means of the high frequency induction heating apparatus developed by the authors, into which the cooling system is incorporated.
The image processing analyzer is used effectively to collect the image data from the isochromatic fringe patterns around the crack tip. These data are analyzed using the overdeterministic method. The results estimated for the thermal stress intensity factors are shown in diagrams.

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Two-dimensionsl image processing is usually used in analysis of the images captured by optical methods. The ability of computers has been remarkably progressed in memory space and processing speed. Three-dimensional image processing is now possible with such computers. It is much faster and easier to analyze three dimensional data using three-dimensional image processing rather than using two-dimensional one.
In this paper, a general purpose program of three-dimensional image processing is developed and it is applied to a photoelastic three-dimensional image with the spatial coordinates (x, y) and the angle θ of the crossed polaroids. This image is obtained by changing the angle of the crossed polaroids. Each two-dimensional image data consists of the isochromatics and isoclinics. The three-dimensional image processing separates isochromatics and isoclinics automatically by processing the data along the third axis θ.

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In estimating the strength of materials, it is widely recognized that the stress intensity factors in the vicinity of the crack tip are useful for quantitative explanation of the destruction. Many cracks in construction materials are three-dimensional. Analysis of the stress intensity factors of materials with three-dimensional cracks are therefore of great importance. In thispaper, the stress intensity factors are determined photoelastically with a thick cylinder having a crack in the direction of the circumference or axis on the inner surface being loaded by internal pressure. In the experiments, by using the stress freezing method, inner pressure is loaded at every depth of the crack. The stress patterns at the tip are observed and the fringe orders are determined. The experimental results are analyzed and compared with conventional results reported in the past.

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Stress concentration of the square plate with a rounded square hole is experimentally observed by a reflective photoelasticity. Two-dimensional square hollow models are prepared for lots of form factors on the corner curvature of the rounded hole and the wall thickness of the model. Additionally, the three-dimensional hollow square bar models of the same configuration of 180mm long are made.
Pressure load is applied to the rounded square hole of both models. For three-dimensional model, a special loading apparatus is designed only to give internal pressure. Stress concentrarion parameters are defined and summarized for the corner curvature of the rounded hole and the wall thickness of the model.

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In turbine design, because the joint between the turbine blade and the rotor bears the largest stress, it is important to study the stress at this position. The fir-tree type is one of the most efficient joint configurations for blade fastenings.
Many papers have reported on the fir-tree turbine blade, but these mostly dealt with experiments using two-dimensional analysis and tensile load, rather than centrifugal load. Data are of minimal value if the stress distribution of tensile load is evaluated in the same light as centrifugal load. We therefore experimented on the fir-tree straight entry type with threedimensional stress analysis in frozen photoelasticity. The loading methods were given with both tensile and centrifugal loads.
The results: Radially in both the tensile and centrifugal loads the highest stress concentration point was the tip serration. Axially in the tensile load the stress concentration at the edge was low. In the centrifugal load the distribution was uniform.

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