Aluminum alloy sheet and plate are commonly used in automobile, train, aircraft and so on where lightweight is required. However, lower costs and lighter weight materials are demanded. In order to satisfy the demand for lightweight without changing the material, it is necessary to raise the second moment of area to increase the bending stiffness. The purpose of this study is creating isotropic patterned shell structures to increase the bending stiffness of aluminum alloy sheet and plate. In this paper, patterned shell structures which have the large second moment of area in arbitrary cross sectional dimensions were developed. FEM results and experimental results indicated that the developed patterns reduce by half the weight of sheets under equivalent bending stiffness condition.

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In this paper, the shear response of three-dimensional lattice structure was investigated based on numerical stress analysis, FEM. In particular, effects of number of unit cells in three directions on the mechanical properties (shear modulus G^* and collapse strength τ^*) of lattice structures were discussed based on theoretical analysis and FEM. It is found that the mechanical properties strongly depend on the number of unit cell in three directions x,y,z, and for a flat structure(N_y=1), the deformation pattern in the structure can be classified into two types. The shear modulus G^* for a flat structure obtained by FEM can be estimated by the elementary beam theory with a good accuracy. Also, for a flat structure with slender struts, the collapse is occurred by elastic buckling, and that with relatively thicker struts, the collapse strength agrees well with the theoretical result. Moreover, the cubic structure having the same number of unit cell in x and z directions(N_x=N_z=N) shows a unit curve for the shear modulus G^*, so that the modulus can be estimated by the curve for various cubic structures.

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The radiated sound from the impacted body must have the information with respect to the impact force and the other properties. We have proposed the method in order to identify the impact force and many properties by analyzing the radiated sound from the impacted body. In the present method, the relationship between the impact force and the radiated sound pressure is calculated by using FEM analysis. And, the time dependence of the impact force, the impact placement, the Young's modulus of the impacted body and the radius of the impact bar are identified by using least square method and the measured sound pressure of the many microphones. By the actual experiments, the efficiency of the proposed method is confirmed.

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Loosening mechanism of bolted joint was examined experimentally and numerically. The loosening tests were carried out using Junker's type loosening machine. In the Junker's tests, transverse repeated displacements were applied to the bolted joint with a hexagon bolt and nut, and then a reduction in the axial bolt force was measured. In the FEM calculations, the loosening behavior of the bolted joint was examined for the model of Junker's type loosening machine. In addition, the effects of the flatness and the surface roughness at the bearing surfaces in the clamped part on the reduction in the axial bolt force were examined in the FEM calculations. As the results, the loosening mechanism was elucidated and it was shown that the effect of the nut rotation was important as well as the elastic torsion of the bolt. The amount of the reduction in the axial bolt force was estimated in the FEM calculation taking account of the flatness and the surface roughness. The numerical results were in a fairly good agreement with the measured results. Discussion was made on the loosening mechanism in bolted joints under transverse repeated displacement.

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Mixed mode fatigue tests are conducted using through cracked specimen. Slant through cracked specimens are made where crack angle is 15°, 30° and 45°. It is shown that factory roof is made in all crack tips due to ΔK_III, and crack growth rate decreases by the factory roof. Fatigue crack growth is simulated using S-version FEM( Finite Element Method) using crack growth criteria. It is shown that conventional crack growth criteria are not available to predict fatigue crack growth with factory roof. In authors' previous study, modified new criterion for the prediction of crack growth rate is proposed. In this study, by using new criterion, fatigue crack growth simulation is conducted, and results are compared with those of experiments and discussed.

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A numerical simulation method of electropaintings using boundary element method (BEM) is proposed. The proposing method treats the electrolytic bath filled with paint solution as a Laplace field, and the boundary conditions on anode and cathode surface are given in the form of robin boundary conditions with polarization curves. The growth of paint thickness is described in mathematical formulas as a deposition model at the same time. Polarization curves and parameters in the deposition model are identified through a series of experiments of one-plate paint tests. Taking advantages of BEM in comparison to conventional researches using finite element or finite volume methods, some examples of analysis including a moving cathode problem in an automotive paint line are carried out to show the validity and effectiveness of the proposing method.

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In the previous research, the neutral band model which assumes the undeformed region nearby its neutral plane was devised to estimate the flexural rigidity of a porous resin /Al laminate. In the present research, the neutral band model may be modified as the magnitude of the neutral band factor, which implies the thickness of neutral band, differs from point to point in the beam. By adopting the modified neutral band model to the case for the partial distributed applied load, the neutral band factor can be expressed as a function of the applied length of the distributed load. The magnitude of the flexural rigidity of the porous resin /Al laminate is calculated by equating the applied length to the circular arc length of loading roller of the 3-points bending instruments. The results obtained are good agreement with the experimental ones irrespective of the span length of the 3-points bending test.

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C/C composite materials have many advantages in the characteristic and the weakness of the low impact strength. Therefore, it is important to evaluate impact damage properties and the details of the impact damage mechanism. In this study, the properties and the damage process under the low-speed range is evaluated by using a drop weight impact test. The impact load-deflection diagram and the absorbed energy change for stiffness of specimen is used for evaluating the impact damage. The measured impact load signal is decomposed in approximation components and detail components, and is reduced higher mode of vibration by multiple resolution analysis in wavelet transform. The results are as follows. In impact damage evaluation of C/C composite materials, it is effective for evaluating the damage properties by using the impact load-deflection diagram and the relationship between absorbed energy and the stiffness reduction ratio.

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Friction-stir-welding (FSW) was performed between high strength aluminum alloy A6061-T6 and cold-rolled steel SPCC-D. The FSWed material was aged again at 453 K for 18 ks to recover hardness of A6061 side in the joint. For the joints of the FSWed material and its aged material, the macroscopic features, microstructures, hardness distributions and element distributions were examined in detail. Especially, the microstructures were investigated through electron back-scattered diffraction (EBSD) for the FSWed material. The result showed that no remarkable defect was formed by FSW and the joint was under good condition. The microstructure of A6061 side in the joint became very fine as well as that of SPCC side near the joint. Such fine microstructures contributed to accelerate diffusion of aluminum and ferrous each other through the interface and to maintain the strength of the joint. Furthermore, no brittle compound layer was detected around the interface. As a result, the static strength of the FSWed material was relatively high. Although the hardness of A6061 side in the joint was decreased by FSW, it was recovered by aging and the static strength of the aged FSWed material reached to that of uniform A6061 material.

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The various subloop behaviors for the superelastic deformation of TiNi shape memory alloy were investigated based on the local temperature variation and the surface observation in the tension test. The results obtained are summarized as bellows. (1) The upper and lower stress plateaus during loading and unloading appear accompanying the progress and reduction of the martensitic transformation (MT) band, respectively. In the case of unloading from the upper stress plateau under low stress rate, strain increases due to the progress of the MT band in the initial stage of unloading. (2) If stress is held constant in the upper stress plateau, creep deformation appears. The creep deformation appears based on the progress of the MT band. The volume fraction of the martensitic phase increases in proportion to an increase in strain. (3) If the transformation strain varies in the stress plateau during loading and unloading, the return point memory appears in the reloading stress-strain curve. The progress and reduction of the MT band start from the boundary of the MT band which has appeared in the preceding process. (4) The angle of boundary of the MT band inclined to the tensile axis is 33° for an aspect ratio of 5 and 42° in the central part of the specimen and 37° in the vicinity of the gripping part for an aspect ratio of 10.

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The laser welding methods are widely used for manufacturing the products that the high quality welding conditions are required. Therefore, the establishment of the evaluation method for the melting conditions is desired. In the previous paper, the method by using the features of detected AE signals, when the irradiation energy was changed at the pulse width, was proposed. The results showed the following: (1) The frequency range of the signal of melting is near 300 kHz. (2) The correlation coefficients of the regression equations that evaluate the melting conditions from the AE energy of transversal wave components showed the high value. (3) The high correlations were recognized with the equations that evaluate the conditions by the led largest Lyapnov exponents from the wavelet transform results of the longitudinal wave component. However, it was proven that the frequency range of the thermal shock wave overlaps to the range of the melting, when the temperature rise rate lowers with the decrease of the lamp input voltage. Therefore, the evaluation method in the previous paper is not able to use in case of the evaluation of the melting conditions under the condition for changing the irradiation energy at the voltage. The method for evaluating the melting conditions, when the irradiation energy is changed by the voltage and the pulse width, is proposed in this paper. Concretely, the detected signals in the range (i.e. after 2 ms from the irradiation completion) that the influence of the thermal shock wave fades out, and the temperature of the irradiation part keeps the over melting point are analyzed with chaos and wavelet transform analysis method. The summaries of the result in this study are like the following. The correlation coefficients of the regression equations that evaluate the melting conditions from AE parameters showed the high value. One of the parameters is the correlation dimension Cd of transversal wave component, and the rest are the largest Lyapnov exponent LLy and the correlation dimension Cd of the time fluctuation waveform on the energy rate of the wavelet coefficient of longitudinal wave component. From the above results, it was shown to be possible that the melting conditions can be evaluated with the proposed method in this study, when the irradiation energy is changed by the lamp input voltage and the pulse width.

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New high speed tool steels, referred to as NF1 and NF2, were made experimentally by controlling the chemical compositions in order to improve the fatigue strength and evaluated with cantilever-type rotating bending fatigue test in air at room temperature in very high cycle regime. Larger size of MC-carbide particles were precipitated more in matrix of NF2 compared with those of NF1 and common high speed tool steel, JIS SKH51, due to the addition of more carbon and vanadium. From the experimental result of fatigue test, two kinds of the materials showed clear duplex S-N curve, composed of three or two types of failure mode, such as, a surface inclusion-induced failure mode (S-mode), a subsurface inclusion-induced failure mode without (I-mode) and with granular bright facet (GBF) area in the vicinity of inclusion (IG-mode) depending on the stress amplitude level. Fatigue strength of specimen failed by internal failure mode in the high cycle regime was the highest in NF2, followed by NF1 and JIS SKH51. As the result of discussion for the effect of microstructure of materials on subsurface crack initiation and growth behavior, size of inclusion at crack origin was the same among three kinds of the materials and crack propagation rate of NF2 was slower than those of NF1 and JIS SKH51, because the MC-carbide particles in the matrix acted as obstacle to crack growth. Also it was suggested that M₆C-carbide particles distributed in the matrix did not affect for subsurface crack growth.

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A new monitoring system has been developed to observe the state of a particle-jetting device which is used to prevent wheel slip in a railway vehicle. The particle-jetting detection ability of the proposed monitoring system was examined by conducting bench tests and vehicle running tests. The result of experimental study shows that the proposed system has sufficient detection ability even for the vehicle running condition. During the jetting of ceramic particles, hard ceramic particles collide with the flow detecting device, and wear away the sensing device. The decrease of detection performance was evaluated by the durability tests which were conducted with repeated jetting of ceramic particles. The result of durability test shows that the proposed system has sufficient detection performance after the repeated jetting which is equivalent to twenty years of vehicle operation, and that the proposed system can be used in real operating vehicles.

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There was a concern that weld toe and welding defects can be causes of the enhancement of the reduced fatigue strength due to hydrogen. Thus, the effect of hydrogen on the fatigue strength of weld-jointed tubes was evaluated. The welding defects were intentionally produced by incomplete penetration. The materials were SUS304 and SUS316L. Fatigue test was done in 0.6MPa hydrogen gas using hydrogen pre-charged specimens. For both materials, hydrogen caused no reduction in the fatigue strength of the welded specimens even if the fatigue strength was influenced by the stress concentration of the weld toe and there were crack-like welding defects.

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