Bolt loosening-fatigue tests under small transverse vibrations have been performed to understand the loosening-fatigue characteristics in the long life region. The current study is focused on the influences of the initial clamping forces and the amplitudes of the transverse vibration. Results show that loosening-fatigue life of bolted joint has depended on the amplitudes of the transverse vibration but has not depended on the initial clamping forces in the long life region. Results also show that the loosening fatigue limits almost have been not influenced by the property class of bolts.

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This research is about a statistical diagnostic method for the structural health monitoring which is applicable to existing structures from the present moment. In this method, structural condition is statistically diagnosed by the change of the response surface. The response surface is a regression model of sensor's outputs. The change of the response surface is statistically tested with the F-test. In the F-test, a threshold of normal or fault condition is simply investigated with a theoretical F-probability distribution. Therefore, this diagnostic method only requires data of intact condition and does not require the complicated modeling and information of fault condition. To confirm the effectiveness of the presented method, the health monitoring of jet fans is conducted, In this study, load cells are mounted to a supporting system of the jet fan. The response surface is calculated from time-series load data measured by the load cells. As a result, the structural condition of the jet fan is successfully diagnosed.

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To develop constitutive equations for mechanical ratcheting at elevated temperature, it is useful to examine behaviors of subsequent yield surfaces. A computer controlled testing system for getting subsequent yield surfaces automatically with the biaxial extensometer for elevated temperature and the device of high frequency heating system have been established. The subsequent yield surfaces have been examined experimentally for the initially isotropic materials of SUS316FR stainless steel subjected to mechanical ratcheting under combined cyclic torsion and steady tension at elevated temperature. As the result, the experiments found rotation as well as translation and distortion of the subsequent yield surfaces during mechanical ratcheting. An anisotropic yield Criterion for mechanical ratcheting is newly proposed in this paper.

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Fatigue tests were conducted for a series of ultrafine grained steels comprising ferrite grains below 1μm. The base ultrafine grained steel contained 0.15% and the C added version contained 0.45% of carbon. 0.1% of phosohorus was added to the P added versions. For each ultrafine grained steels, as-rolled and annealed versions were prepared since the as-rolled version was work-hardened. As the result, tensile strength of the prepared ultrafine grained steels ranged from 721 to 1048 MPa. All of the prepared ultra fine grained steels showed high fatigue strength and the fatigue limit ratios (fatigue limit/tensile strength) exceeded 0.5. The faitigue strength of ultrafine grained steels was higher than that of ferrite-pearlite steels, and as high as that of tempered martensite steels.

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The evolution of dislocation structures during cyclic plastic loadings is investigated. The loading paths of cyclic plastic loadings conducted in this study are tension-compression, torsion, cruciform, and circular loading under constant strain amplitudes. The dislocation structures of the specimens after the cyclic loadings are observed by Transmission Electron Microscope (TEM). The meso-structures, the dislocation structures of five neighbourhood grains, are also observed to verify the inhomogeneity of deformation of polycrystalline metals. Finally the relationships between cyclic plastic loadings and the evolution of dislocation structures are discussed.

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The present study investigates plasticity-induced martensitic phase transformation around part-through cracks in a nonmagnetic austenitic stainless steel SUS 304 fatigued at room temperature in air. Spatial distributions of the volume fraction V_<α'> of α' martensitic phase around semi-elliptical fatigue cracks emanating from artificial notches having different aspect ratios were measured with ferrite scope. The results were compared with the distributions of vertical magnetic flux density B_z above the cracks in the specimens magnetized by a strong electromagnet. It was revealed that the B_z distributions above and below the surface cracks reflected the α' phase distributions in the plastic wake regions produced around the cracks: i.e., the distance between the points where B_z reached the maximum and the minimum values B_<zmax> and B_<zmin> had linear correlations with surface crack length 2a. The B_<zmax> and the B_<zmin> values also showed linear relations with maximum stress intensity factors at the surface tip K_<amax> and at the depth position K_<bmax>. Each relation, i.e., 2a vs. 2l, B_<zmax> vs. K_<amax>, etc. can be represented by a single straight line regardless of the stress ratio and of the aspect ratio of initial notches.

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The present paper describes the fatigue behaviour of prestrained type 316 stainless steel. Two types of fatigue tests, S-N test and stress-incremental test, were performed under rotary bending using specimens subjected to 5% and 15% tensile prestrains. Fatigue strength increased with increasing prestrain, with 7% and 27% increase of fatigue limit in the 5% and 15% prestrained specimens, respectively, compared with the unprestrained specimen. The increase of fatigue strength in the prestrained specimens was attributed to higher crack initiation and small crack growth resistance. Under stress-incremental tests, the fatigue limits were increased significantly in the unprestrained and 5% prestrained specimens, but no increase was seen in the 15% prestrained specimen. Remarkable increase in hardness of failed specimens was recognized in the unprestrained and 5% prestrained specimens, while only a slight increase in the 15% prestrained specimen. It was believed, therefore, that the coaxing effect was strongly related to the ability of work hardening during stress cycling.

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