Two models of micro-photoelastic equipments are made for trial by improving of a metallurgical microscope. One of them is reflective and the other is transparent model. The sensibility of the former model is twice compared with the latter. A test piece is soaked in a liquid bath which has the same refractive index. Photoelastic fringes can be observed clearly in a monofilament with 200-400μm in diameter. At its necking part the fringe pattern shows sometimes anomalous fringes in process of stretching. The analysis of its fringe was carried out by numerical integration. Then, at the early stage of stretching, the periphery of monofilament was elongated more than the inner part, but finally its elongation becomes uniform. Moreover, practical applications were performed preliminary with polymer monofilaments under some atmospheres.

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An interferometric-photoelastic study has been made of inplane contact between two plates with a circular edge. An interferometric-pattern furnishes both isopachic and isochromatic fringes simultaneously which provide necessary and sufficient information for the complete determination of principal stresses σ₁ and σ₂ for the overall field. Oil immersion procedure is employed to eliminate the disturbance of the light ray due to the thickness change of the model plate and to obtain finely and properly defined fringes even in the utmost stressed region. Special emphasis of the investigation iS laid on elucidating the distribution of tangential stress σ_s (σ₁) along the contact line, particularly the value of maximum tensile stress (σ_s) t max which occurs at the end of the contact patch. The relationship between (σ_s) t max and the shape factor of the plates R₀/R with the length of contact b/R₀ as a parameter is given.

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The dynamic stress distribution, crack initiation and propagation at the bottom of the notch under impulsive bending load were investigated by using the dynamic photoelastic method repeatedly and the velocity gage method. Photoelastic coatings were bonded to the resin mortar plates and aluminum alloy specimens, and these specimens were loaded dynamically by the falling impact indentor. Isochromatic patterns in the coating resin were satisfactorily taken at various stage of impact of the test pieces by the ultra high-speed camera, that is the image converter camera IMACON-790. The measurement of fracture speed made in this way was compared with an alternate technique in which an array of electrically conducting paint stripes was arranged on the other surface so as to signal an open circuit on crack arrival. Finally, it is shown that the photoelastic coatings are very much useful to enhance surfacecrack visualization subsequent to impact, and that the maximum propagating velocity of the crack in the resin mortar is about 900m/s.

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The propagation of polarized light in a 3-D photoelastic medium and a weakly inhomogeneous absorbing anisotropic and optically active medium is investigated on the basis of the equation ∂s/∂z=Ω×s+ (T×s) ×s and the Poincaré sphere. Here, s is the unit polarization vector, z is the propagation distance along a light path. The symbols Ω= (Ω₁, Ω₂, Ω, ) and T= (T₁, T₂, T₃) are defined as the birefringent vector and the dichroic vector, respectively, representing the birefringence and the dichroism of the medium. Some evolutions of polarizalion states are drawn on the sphere for such media having arbitrary constant vectors Ω and T. Some conventional and main equations of 3-D photoelasticity are represented by the unit polarization vector. The properties of the resulting equations are considered with the help of the Poincare sphere and computer drawings of the evolution of polarization states.

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Since the work of Post et al. in the early 50's on application of photoelasticity to fracture mechanics, many investigators have reported the photoelastic methods of determining stressintensity factors for the purpose of applying fracture mechanics to actual design problems. In some of these reports, we can see that several methods of using photoelastic isochromatic fringe data have been proposed. However, the paper to discuss the merits of those ones has not been seen except the critical review by Etheridge and Dally. In the present paper, double check of those ways of determining the stress-intensity factor (K_I) from isochromatic fringe data was made and that was compared with the three methods (the method I, II and III) proposed by the authors in order to find the most accurate one among them. The result shows that, if we put them in order with regard to smallness of the average error determined from each eleven test measurements, those become Smith's method, Irwin's, the method II and the slope method, and so on. Since practice or experiences in this field for a long period would make it possible to acquire better accuracy in the K_I determination, its measurement should be put into a skillful analyst's hands and also, we should be careful not to take inaccurate measurement of the distance of an isochromatic fringe from the tip of a crack.

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Research data of the singular point in the photoelastic experiment is insufficient, and there still remains a wide unexplored domain. This paper deals with an interesting conclusion reached by comparing experiments regarding the isotropic points along the symmetric section of centrally-concentrated loaded beams with the results of calculation. A single isotropic point is formed when the ratio of span to depth is 4.3, and two isotropic points are developed for all ratios greater than 4.5. No isotropic point exists for the ratios less than 4.3, but a single isotropic point appears again when the ratio is 0.8. Furthermore, this paper deals with the properties of isotropic points from the experiment described above.

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A method is proposed for the determination of the internal stresses in a two-dimensional system from data furnished by a photoelastic analysis. The method involves the numerical integration of the Laplace and Poisson type difference equations over a region with known boundary values by the iteration of a set of calculus of variations formulas. In this the complete system of internal stresses is computed, using the data obtained from the usual fringe photograph, without recourse to isoclinic lines, or other supplementary experimental measurements. Comparison of the calculated results and those obtained from elasticity shows close agreement.

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