Photoplasticity is a full-field technique that is based on the interpretation of optical patterns in transparent birefringent materials that have been stressed beyond their elastic limit. Polycarbonate resin, a photoplastic model material, has been subjected to much study. In this study, we attempted to investigate the dependence of the stress-strain curves of polycarbonate resin on temperature and tensile speed at high temperature, to find the best temperature for plastic strain freezing. We also considered whether the theoretical equation of Ramberg-Osgood could be applied to the stress-strain curve that was obtained by photoplastic experimentation. Therewith, the aim of next study is an examination of the possibilities of the plastic strain freezing method in comparison with the elastic stress freezing method. First, we attempted to determine the best temperature for plastic strain freezing. Further, it became apparent from systematic experimental results that it is 'strain' and not 'stress' which is frozen in plastic regions. In other words, it was made clear that the Birefringence N in strain freezing was proportional to the difference in the principal strains (ε₁-ε₂).

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Recently the fiber reinforced plastics (FRP) consisting of carbon and aramid fibers have come to be used as structure components of spaceships etc. From the viewpoint of mechanical properties such as elastic modulus, tensile strength and ultimate strain, each of these fibers has its own advantages and disadvantages, e. g. carbon fibers have high elastic modulus and high tensile strength but low ultimate strain, and aramid fibers have high ultimate strain. By combining fibers of different types, hybrid FRP having specially required mechanical properties can be obtained. Meanwhile the mechanical behavior of matrix resin of FRP changes generally with time and temperature, that is, viscoelastic behavior. Therefore, it can be also considered that the fracture behavior of hybrid FRP changes with time and temperature remarkably. In this paper, a materials design guideline of hybrid FRP is reviewed from the viewpoint of laminate constitution and viscoelastic behavior of matrix resin based on the research works of authors about the mechanical behavior of carbon/aramid hybrid unidirectional FRP laminates.

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An optimum design method of fibrous laminated composites is proposed. This method yields optimum laminate configuration with the maximum strength being subject to required in-plane stiffness under in-plane loading condition. Tsai-Wu criterion is used for determining a first-ply-failure strength, and the margin of safety is adopted as the objective function in optimizing process. The fiber orientation angles are 0°，±45°and 90°, which are usual for aircraft structures.

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There are many studies on natural frequencies of structural systems, where the system is treated as quasistatic. In the viewpoint of safety and reliability, however, dynamic responses become important. The less cycles of stress variations to a material are, the less fatigue is stored in it by the fatigue failure theory, and the body has relatively longer lifes. Therefore, it is desirable for a structure with damping, which is subject to a vibration, that a rate of amplitude reduction is larger. This study considers a shape design problem of structures, and aims to maximize their damping ratios. As a numerical treatment, Finite Element Method and Method of Modal Analysis are applied for beams, and a simple optimization scheme which uses the sensitivity analysis is proposed. The shapes obtained are different from each other depending on values of Rayleigh coefficients.

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A method of evaluating effective failure path of multiple layer composites laminates under off-axial load condition is presented. It is necessary to select the important failure path whose occurence probabilities are greater than the others since the number of failure path of multiple layer composite laminate is great deal of number of combination of failure path. The proposed procedure of selecting effective failure path depends upon the branch and bound rule. An extended study is examined in order to estimate the failure probability of laminate from resultant effective failure path. Some numerical analysis based on the proposed algorithm are represented to graphite/epoxy composites laminates (T300/5208).

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This paper is intended to propose a new technique based on linear-photoviscoelastic theory on the stress freezing method in order to improve the accuracy of measurement. Three functions for evaluating the accuracy of measurement on the stress freezing method are newly defined. The method for optimizing the temperature and loading conditions during stress freezing process is induced from linear photoviscoelastic theory. The availability of this method is confirmed experimentally by four-point bending-test of epoxy beam.

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Failure mechanisms of short glass fiber reinforced poly(ethylene terephthalate) were investigated with particular attention to the effects of fiber volume fraction (V_f＝1 wt.%, 30 wt.% and 60 wt.%). A fracture morphology study was carried out for the surface and for the interior of uniaxial tensile specimens. On the surface, tensile cracks occurring mostly at the fiber ends seemed to be more influential in catastrophic fracture initiation with decreasing V_f. However, the failure mechanisms in the interior were different from those on the surface. For specimens of low V_f (1wt.%), shear bands grew around the fiber ends. A "specific layer" was formed in the matrix along the fiber-matrix interface and shear cracks propagated near the fiber interface in the fiber length direction. The fiber pull-out from the matrix as well as the voiding at the fiber ends, induced by the shear cracks, had strong effect on the fracture initiation. For intermediate and higher V_f (30 wt.% and 60 wt.%), the shear-band induced cracking near the interface caused matrix shear cracking which was the most influential factor in the fracture initiation.

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Square plate of laminated glass, whose interlayer is the polyvinyl butyral, are impacted transversely by a circular steel ball. The impact critical energies U_c and U_p which are the energy to initiate a crack in the outerlayer glasses and penetration energy of the ball, are measured by changing the dropping height of the ball. The static bending strength and U_c are depending on the total thickness T of glass in the laminated glass. But, U_p is independent of T and depends on the thickness of the interlayer. The penetration fracture of the laminated glasses consists of three steps. The first step is until initial cracks initiate in the outerlayer glasses, the second fracture is the bending fracture of the laminated glass and the third is the fracture due to shearing the interlayer. Considering the relationships mentioned above and material properties of the laminated glasses, we can propose the penetration formula for estimating U_p. The validity of this formula is discussed in terms of the results of experimental and theoretical examination.

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Metallic materials for machine structural use are usually composed of a number of fine crystal grains, and the crystallographic orientation of individual grain indicates the characteristic distribution pattern depending on the fabrication process. For the metal annealed sufficiently, the orientation is supposed to distribute at random in the material space. When the cyclic loading is applied to such a polycrystalline metal, slip bands are observed in the respective grains on the specimen surface. The orientation of each slip band is determined by the combination of the loading direction and the slip system of the crystal. In this study, the slip bands formed on aluminum sheet specimens under the cyclic loading were carefully observed for a number of surface grains by an optical microscope, and the probabilistical analysis was developed on the distribution characteristics of the slip band orientation. The analytical distribution thus obtained was in good agreement with the experimental results on the orientation distribution of the slip bands.

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All plastic optical fiber (APF) has been usually applied in the field of short distance optical signal transmission. However, heat-resistance of commercial APFs is so low that their application has been limited. In this paper, core of APF was made from crosslinked polymer. In order to make clear the controll factors of APF's properties, fabricating condition, crosslinking density and others were studied. As a result, the heat resistance for optical fiber is relate with the deformation during heating. Drawn fibers are deformed by heating and their light tansmittances are reduced by deformation. On the other hand, undrawn and crosslinked core fiber shows excellent heat resistance, because it has never been elongated in fabricating process. And the developed fiber has the desirable mechanical characteristics, along with chemical durability.

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The ratios of residual deformation of epoxy resins which the silica is filled and the silica is filled with graphite are measured by changing the glass transition temperature and are compared with the ones of phenolic resins with particulate fillers of same kinds and quantities. The results obtained are shown as follows :
(1) The ratios of residual deformation of particulate filled epoxy resins decrease with an increase in the glass transition temperature.
(2) The ratios of epoxy resins which the silica is filled with graphite are lower than the one of epoxy resins which have a same glass transition temperature and the silica is filled, but the ratios of particulate filled phenolic resins show a different tendency to the ones of the particulate filled epoxy resins by the kind of filler.
(3) The secular change of particulate filled epoxy and phenolic resins can be estimated by the master curves of the residual deformation. It is found that after 20 years a ratio of residual deformation of epoxy resin which the glass transition temperature is higher and the silica is filled with graphite is lower than the one of phenolic resin which the silica is filled.
4) The tendency described above for the ratios of residual deformation can be found by the activation energy and crosslinking density instead of the glass transition temperature.

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