In order to investigate a fatigue properties of SiC/SiC composites, tensile tests and the low cycle fatigue tests of SiC/SiC composites were carried out at room temperature. Two types of SiC/SiC composites were manufactured for the tests. Tensile tests were conducted with a loading rate 0.02,1,10MPa/s to investigate the relationship between the ultimate strength and a loading rate. As a result of tensile tests, it was seen that ultimate strength decreased with a loading rate. Low cycle fatigue tests were conducted with a frequency 0.02Hz and R=-1 with strain-controlled and stress-controlled conditions. As a result of low cycle fatigue tests, it is seen that the SiC/SiC composites offered cyclic softening behavior and the relationship between the strain range and the fatigue live was evaluated as Manson-Coffin's relation.

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In order to clarify the influence factors on high-cycle fatigue of high strength steel SUJ2, the fatigue test have been carried out up to 10^8 cycles under rotating bending at room temperature. According to the experimental results, in the case of comparative low-cycle range, the fatigue crack initiates from specimens surface. On the other hand, in the case of high-cycle range, the crack initiates from an internal inclusion. In addition, there exisits transitional zone in the S-N curves between surface failure and fish-eye one. The damage, which means slipping would be accumulated in the specimen's surface under the high stress amplitude during two step stress fatigue. In addition, according to the above phenomena, surface appears in the region of extra-high cycle fatigue. According to the observation results, slip bands are generated in the spoecimen's surface. That is to say, speaking of failure form cause of surface hardness and surface damage.

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This present study was done with the aim of improving the reliability of quantitative ultrasonic nondestructive testing. The water immersion ultrasonic method, using an oblique longitudinal wave with large incidence angle (over the critical angle), was applied to measure small surface fatigue crack due to low-cycle loading. Surface fatigue crack initiation process, beginning from persistent slip band initiation, was measured using ultrasonic microscope. To estimate the precision of measurement, four transducers with different frequency, they are 5,10,20 and 50MHz, respectively, were used to make clear the relation between the ultrasonic frequency and its minimum detectable size of surface fatigue crack.

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A nonlinear acoustic measurement is studied for fatigue-damage monitoring. An electromagnetic acoustic transducer (EMAT) magnetostrictively couples to a surface-shear wave resonance along the circumference of a rod specimen during rotating bending fatigue of carbon steels. Excitation of the EMAT at the half of the resonance frequency caused the standing wave containing only the second-harmonic component, which was received by the same EMAT to determine the second-harmonic amplitude. Thus measured surface-wave nonlinearity always showed two distinct peaks at 60 % and 85 % of the total life. We attribute the earlier peak to the crack nucleation and growth, and the later peak to an increase of free dislocations associated with crack extension in the final stage.

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Analytical approaches to the modeling of elastic wave propagation in solids are difficult to apply in the ultrasonic nondestructive testing (NDT) systems, where one is interested in predicting realistic transducer signals from ultrasound interactions with complex defect shapes. This report presents a finite element formulation for an overall ultrasonic NDT. Viscous boundaries are introduced to limit the problem domain to part of a tested material. These make it possible to reduce computational costs.

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The electromagnetic acoustic transducer(EMAT) for Lamb wave, which consists of a meander coil with a distance of 2.5mm between two channels and has a symmetrical structure in the vertical direction for both surface sides of a thin steel sheet, has been researched as a flaw detector of thin steel sheets. This EMAT can generate some Lamb waves with variable wavelengths and multiple modes, and can separately generate symmetrical or anti-symmetrical mode Lamb waves.

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Changes in shear wave velocity were measured by the sing-around method rotating the oscillation direction of the wave with respect to the orthotropic axis of wood. The velocity of the shear wave propagated through the stressed wood decreased suddenly when the oscillation direction coincided with the tangential direction of the wood. The polarization direction of shear wave coincided with the principal axes of wood, not with the direction of the principal stresses. This finding indicated that the polarization direction was much affected by the texture-induced anisotropy of wood. Based on the result, the bending and shear stress distributions in wood beam specimen were estimated by the acoustoelastic birefringent method. The stress values estimated agreed well with those obtained by the strain-gauge method and mechanical calculations.

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It was found out that a local collar could be formed on a rod by a combination of compression, bending and axial-rotation temperature rise in collar forming process was below 15℃ in spite of super plastic deformation. This collar forming method is a technology that Baushinger effect can be applied to form collars by giving altemate bending stress of tension and compression to a rod subjected to axial stress slightly below yield strength.

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Meso-mechanical material modeling of super plastic metal alloy is attempted. Multi-crystal grains in the metal that exibit extensive surface sliding is modeled by setting a tangential spring layer between the grain and the matrix. The constitutive law for the domain in which mult-phase crystal grains of the type are dispersed is derived with the use of equivalent inclusion method on the basis of self-consistent shceme.

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We numerically analyze slip deformation in models of dual phase materials that contains a plastically-deformable or plastically-non-deformable inclusion, and compare dislocation structures in the vicinity of each inclusions. The results show that the hardness of inclusion does not have large effect on the structure of dislocations outside the inclusion. On the other hand, distribution of normal stress in inclusion show large difference between the plastically-deformable inclusion model and the plastically-non-deformable inclusion model. We discuss the relationship between development of slip deformation and stress, distribution in inclusion.

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