The superconducting magnetic levitation (Maglev) systems for trains running at higher speeds than the Shinkansen trains, which represent the high-speed railway in Japan, have been developed. In order to achieve the levitation running, the reduction in weight for the Maglev vehicles is required, and therefore aluminum alloys are applied to bogie frames, while steels are still used for the conventional railway. Considering that the strength of aluminum alloys is relatively low, the safety and reliability method for designing the bogie frames made of aluminum alloys was newly introduced, fulfilling the requirements for the application, such as load conditions and strength conditions. From the results of bench tests, including metal fatigue tests, after trial manufacture and running tests in Yamanashi Maglev Test Line, it was verified that the new design method based on quality control was established.

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Threaded fasteners are widely used in mechanical structures since the disassembly for maintenance is easy and low cost. However vibration-induced loosening due to dynamic loading has remained to be problematic. Various kinds of anti-loosening components such as spring washer, flange nut and double nut have been proposed and used in order to prevent loosening. In this paper we have evaluated the loosening proof performance of plain washer and flange nut under the condition of shear loading by three-dimensional finite element analysis. As for the loosening induced by bearing-surface slip, it is found that both plain washer and flange nut show no loosening proof performance. As for the loosening induced by micro bearing-surface slip, the plain washer shows lower critical loosening load and higher loosening rate, as compared with conventional nut. Although the critical load of flange nut is similar with that of conventional nut, the loosening rate is smaller. Therefore, it can be concluded that plain washer and flange nut show negative and positive loosening proof performance, respectively. It is also found that critical slip width Scr is not suitable for the evaluation of the loosening under force-controlled loading condition. In order to evaluate the loosening proof performance, critical loosening load and loosening rate must be investigated from the viewpoints of both bearing-surface slip and micro bearing-surface slip.

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Polycrystalline piezoelectric materials have a large possibility to exhibit higher performance ina macroscopic scale by design of crystal morphology in a microscopic scale. In this paper, a multiscale finite element method by using crystallographic homogenization method has been applied to a typical piezoelectric ceramics, barium titanate (BaTiO₃) in order to estimate macroscopic properties considering microscopic crystal morphology. Then, microscopic crystal orientation distribution has been optimized by steepest decent method to maximize macroscopic piezoelectric strain constant d₃₃₃. Computational results indicated that BaTiO₃ polycrystal consisting of three layers with different crystal orientations has the highest piezoelectric performance d₃₃₃=258 pC/N, that is beyond single crystal because of mechanical effect in microscopic inhomogeneous structure.

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The digital engineering is considered as a powerful technology for improving the competitive power of products. Especially the optimal design is an important technology for it. The products, which have the competitive power, usually have core technologies in the design and manufacturing fields. The spot weld technology, such as positions and number of spot welds on white-body, indicates the technological level of automotive company. This technology is typical core technology. Authors proposed a new hybrid meta-heuristic method by reflecting recognition of dependence relation among design variables automatically. The proposed method was applied to some benchmark functions to check its performance, and was confirmed that it improved an amount of computational cost and convergence up to the optimal solution. In this paper, authors apply the proposed method for an estimation of it to the optimization of spot welding positions which is an actual engineering problem. The effectiveness of the proposed method is discussed through the optimization of spot weld positions for application of engineering problems.

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It is important to consider the interaction between multiple cracks for evaluating the reliability of structures. In this study, the stress intensity factor (K value) calculated from finite element method is used for evaluation of interacting surface crack. For simplification, it is assumed that neighboring two cracks with various aspect ratios have same dimension and located parallel. Interaction criterion for coalescence of two cracks is set as 10% amount of rise of maximum value of K value. As a result of investigation about the interaction criterion of located parameter, it is confirmed that the criterion is much affected with aspect ratio of cracks. Finally, simple criteria as functions of aspect ratio are obtained.

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Previously several kinds of anti-loosening bolts and nuts were invented; however, they usually need a certain amount of prevailing torque even before the nut touches a fastened plate. A new outer cap nut named “Super loose proof (SPR)” has been developed to overcome such inconvenience. At first this outer cap nut can be rotated smoothly by hand until the nut touching the fastened plate; however, after fastening the outer cap nut, anti-loosening performance can be realized by deforming the outer cap and producing thread contact force at the outer cap region. In this study, stress concentration and tightening-loosening behavior are analyzed by axi-symmetric and three-dimensional finite element methods. Under a certain bolt-axial force, the load distribution of 1st pitch decreases more than 12% with increasing initial clearance of outer cap nut. Stress concentration appearing at the 1st pitch of the bolt can be about 10% smaller than that of conventional nut, reflecting the increase of the thread contact force at the outer cap region. On the other hand, it is found that anti-loosing performance of SPR can be realized when the outer cap has high yield stress.

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This paper is concerned with a dual reciprocity boundary element method (DRBEM) applied to the transient heat conduction problem of anisotropic materials. The integral equation formulation employs the fundamental solution of Laplace equation for isotropic materials, and hence from the anisotropic part of the governing differential equation a domain integral arises in the boundary integral equation. This domain integral is transformed into boundary integrals by using new radial basis functions. Furthermore, time derivative is approximated by the finite difference method, and the domain integral also appears from this approximation. Such a domain integral at each time step is also transformed into boundary integrals via the same dual reciprocity method. The details of the proposed DRBEM are presented, and a computer code is developed for two-dimensional problems. The usefulness of the present method is demonstrated through comparison of the results obtained by the computer code with the analytical ones.

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This paper is concerned with an application of the boundary element method using Green's theorem to analyze nonlinear transient heat conduction in anisotropic solids. In this study, as the fundamental solution of this problem is not obtained, the concept (Analog Equation Method) proposed by Katsikadelis and Nerantzaki is applied. A standard linear partial differential operator in which the fundamental solution can be obtained extracts from a nonlinear partial differential equation. One can consider the remainder as a body force and transform a domain integral into a boundary integral using Green's theorem. Mathematical formulations of this approach for two-dimensional problems are presented in detail. The proposed solution procedure is applied to a couple of typical examples, and the validity and other numerical properties of the proposed BEM are demonstrated through discussions of the results obtained.

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The Preisach model is applied to hysteresis of required energy for reorientations of martensitic variants of shape memory alloys. To express tension-compression asymmetric behavior, three variants are considered, which are the thermal induced, the tensile stress induced, and the compressive stress induced martensitic variants. Residual stresses due to unconformity at interfaces between grains are also considered into the energy. Stress-strain hysteresis loops for a bar under tension-compression cyclic loading are simulated and they are compared with available measured data. Results show that this model can capture quite well asymmetric stress-strain deformation behavior for tension and compression and difference in stress-strain relationship between the first and the second cycle. This indicates that the proposed model can be used for explanation of the deformation behavior of shape memory alloys and for design of structural elements with shape memory alloys.

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Influences of stress ratio on constant amplitude fatigue behavior of CFRP laminates have been examined and a rational fatigue life prediction method has been developed. First, constant-amplitude fatigue tests are performed at room temperature on a quasi-isotropic CFRP laminate [45/90/-45/0] _2s for six kinds of stress ratios. The experimental results show that fatigue strength is lower for fatigue loading with larger amplitude. It is observed that the stress amplitude for a given fatigue life becomes largest under a fatigue condition in which stress ratio is equal to the ratio of compressive strength to tensile one. A procedure to construct a nonlinear constant fatigue life (CFL) diagram is developed on the basis of the static strengths in tension and compression and the reference S-N relationship for a critical stress ratio equal to the compression-tension static strength ratio. The fatigue lives predicted on the basis of the nonlinear CFL diagram agree well with the experimental results over the range of fatigue life up to 10⁶ cycles for all the stress ratios tested. It is demonstrated that the proposed fatigue life prediction method can also be successfully applied to the fatigue behavior of different types of CFRP laminates [0/60/-60] _2s, and [0/90] _3s.

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In order to investigate the effect of frequency on the crack growth behavior, ultrasonic fatigue tests were carried out for an extruded age-hardened Al alloy, 7075-T 6, in ambient air and in N₂ gas, and the results were compared with those in rotating bending fatigue. Fatigue strength was higher in ultrasonic fatigue than in rotating bending one. This was caused by the retardation of a crack initiation and its early propagation. In ultrasonic fatigue, the growth direction of a crack changed macroscopically from a tensile mode to a shear one which the direction was about 35 degrees against to the specimen axis, and fracture mechanism also changed from striations to transgranular facets with voids microscopically. Crack growth rate at the transition of crack growth direction was about 3 × 10^-9 m/cycle. The relation between an applied stress σ_a and a crack depth at the transition of crack growth direction b_T was expressed by σⁿ_ab_T=constant. These results were explained from the time dependent environmental effect and texture of microstructure.

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Fatigue life prediction of solder joints is one of the most important areas of research in the development of reliable electronic packages. In the present study, a new method of estimating the crack propagation, which is based on finite element analysis without geometrical crack model, was examined. On the basis of a damage model assumed for solder, the new method called 'damage path simulation' was verified for solder joints in QFP (Quad Flat Package). It was clear that the extension of the damage path showed good agreement with the behavior of crack propagation observed in the actual thermal cycle tests. Damage path extension from a pointed end of outer lead was also simulated simultaneously with that from the upper surface of the solder fillet, and both damage paths were finally combined. The advantage of the proposed method was especially evident when the fatigue cracks were initiated from two or more regions. The effects of the frequency of thermal cycle were also discussed. It was shown that the frequency of thermal cycle has a noticeable effect on the crack propagation rate. It was concluded that the estimation of the crack propagation in solder joints based on the proposed method is satisfactory for engineering purposes.

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Cavitation erosion was studied for pure tianium (TB270H, TB340H, TP49H) and stainless steel (SUS316L) samples using a rotating disk apparatus in seawater and tap water. In addition, identical experiments for titanium alloy (Ti-6Al-V, Ti-15V-3Cr-3Cn-3Al) samples were carried out in salt water (3%) and ion exchange water using a vibratory apparatus. Erosion resistance of pure titanium in seawater is excellent, as it is in tap water, but the incubation period in seawater is shorter than that in tap water. Erosion resistance of stainless steel is excellent in tap water, but it is necessary to advance the time for its inspection when stainless steel is used for the seawater pump impeller material because the resistance decreases remarkably in seawater. Normalized erosion resistance of these metals using a rotating disk and a vibratory apparatus can be evaluated similarly in terms of Vickers hardness (HV) when it is arranged using a standard material.

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Cavitation erosion tests were carried out by using vibratory apparatus to obtain MDE (Mean Depth of Erosion) and MDER (MDE Rate) curves for pure aluminum and aluminum-base alloys. The relation between the surface profile and impact load of cavitation was studied. Since aluminum alloys are very soft materials, the surface roughness increases with exposure time to cavitation. The impact loads on the specimen surface decreases with increased roughness, and the deceleration stage of MDER curves appears. It was concluded that the erosion rate d with exposure time can be expressed by four parameters α, β, c, and k in the following equation.
d= (α/β) {1/ [1+ (α/β) ce^-at+kt]}

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In our previous studies, it was revealed that the adhesive strength of TiN film deposited on the steel substrate was drastically improved by the substrate quenching after TiN coating. In order to investigate the mechanisms of the improvement of the adhesive strength by such the substrate post quenching, the depth profile of atomic concentrations near the interface between TiN film and the steel substrate was investigated by rf glow discharge optical emission spectrometry (rf-GDOES). It was confirmed that the atomic diffusion at the interface was promoted and the thickness of the diffusion layer increased by the substrate post quenching. A good correlation was recognized between the variation of the adhesive strength with increasing the heating time in the substrate post quenching and the variation of the thickness of the diffusion layer. From these results, it was concluded that the main reason why the adhesive strength was improved was the increase of the thickness of the diffusion layer in the heating process of the substrate post quenching.

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Considering a rational maintenance rule of Light Water Reactor piping, reliable flaw evaluation criteria are essential to determine how a detected flaw is detrimental to continuous plant operation. Ductile fracture is one of the dominanant failure modes to be considered for carbon steel piping, and can be analyzed by the elastic-plastic fracture mechanics. Some analytical efforts have been provided as flaw evaluation criteria using load correction factors such like the Z-factors in the JSME codes on fitness-for-service for nuclear power plants or the ASME boiler and pressure vessel code section XI. The present correction factors were conventionally determined taken conservatism and simplicity into account, however, the effect of internal pressure which would be an important factor under an actual plant condition was not adequately considered. Recently, a J-estimation scheme, “LBB. ENGC” for ductile fracture analysis of circumferentially through-wall-cracked pipes subject-ed to combined loading was newly developed to have a better prediction with more realistic manner. This method is explicitly incorporated the contribution of both bending and tension due to internal pressure by means of the scheme compatible with an arbitrary combined loading history. In this paper, the effect of internal pressure on the flaw evaluation criteria was investigated using the new J-estimation scheme. A correction factor based on the new J-estimation scheme was compared with the present correction factors, and the predictability of the current flaw evaluation criteria was quantitatively evaluated in consideration of internal pressure.

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In this study, singular fields at the ends of fibers are discussed by the use of models of rectangular and cylindrical inclusions in a semi-infinite body under pull-out force. The body force method is used to formulate those problems as a system of singular integral equations where the unknown functions are densities of the body forces distributed in a semi-infinite body having the same elastic constants as those of the matrix and inclusions. Then, generalized stress intensity factors at the corner of rectangular and cylindrical inclusions are systematically calculated with varying the elastic modulus ratio and aspect ratio of inclusions. The effects of elastic modulus ratio and aspect ratio of inclusion upon the stress intensity factors are discussed.

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This paper contains an analysis of the stress and displacement distribution arising in a strip with a circular inclusion when the strip is subjected to bending at infinity. Two types of inclusion, i.e., perfect bonding and sliding inclusion are treated in this paper. The solution which is based on the Papcovich-Neuber displacement potentials is obtained by combining the harmonic potentials in integral forms and infinite series. The boundary conditions of the problem are fully satisfied using the relationships between the harmonic functions of Cartesian and polar coordinates. The effect of the inclusion on the stress and displacement are given in the form of graphs to show the availability of the present method.

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The effects of injection-molding conditions and interfacial structures on the shear welding strength of polyamide material were investigated and the following main results have been obtained. (1) Variations of the first injection-molding speed and temperature exert an influence on the welding strength when the secondary injection-molding temperature T₂ is low (below T₂=265°C), but the influence vanishes when T₂ is higher than 285°C. (2) Under any first injection-molding condition, the welding strength intensifies with the increase of secondary injection-molding temperature, and the highest welding strength reaches 45 MPa, which is almost the same as that of the non-welding base material. (3) It greatly influnences the welding strength that a trans-crystal which is perpendicular to the welding interface is formed in secondery molding. When T₂ is higher that 285°C the trans-crystal layer is formed in the whole welding interface and a stable high welding strength may be obtained. Above results show that it is possible to obtain a high shear welding strength close to that of base material by controlling welding conditions in the injection welding method applied in the present research.

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