When we estimate the fatigue life of lead-free solder joints, we have to conduct FE analysis using a constitutive model which can exhibit mechanical properties of lead-free solder. In FE analysis of solder joints under cyclic temperature load, a constitutive model has to express stress strain curves, stress strain hysteresis loops and stress relaxation curves accurately, containing these temperature dependencies and these rate dependencies. In this study, we proposed a separate type viscoplastic-creep constitutive model which can describe stress strain curves, stress strain hysteresis loops and stress relaxation curves, with these temperature dependencies and these rate dependencies. We implemented the proposed model into finite element analysis code ABAQUS. We conducted tensile tests, tension-compression tests and tension-stress relaxation tests of Sn3.5Ag0.5Cu0.07Ni0.01Ge solder and determined material parameters of the proposed model from tensile test data and tension-compression test data. Then, we analyzed the conducted material tests using the proposed model and compared FE analysis results with experimental test data to examine the validity of the proposed model. It was confirmed that analytical results were in good agreements with the experimental ones.

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The contact gasket stress distribution in a wavy oil-pan shaped flange connection under the internal pressure was examined using finite element method (FEM) for estimating a location where a principal leakage occurred and for calculating the amount of leakage. Leakage tests were also conducted to validate the estimated results using an actual connection under the internal pressure. The effects of flange shape on the contact gasket stress distributions were examined. The sealing performance for the difference types of inner fluid (gas/liquid) was evaluated from the contact gasket stress distributions. It was seen that the estimated amount of leakage was in a fairly good agreement with the measured results. The difference of the contact gasket stress distribution and the sealing performance were shown between the box-shaped flange and the wavy oil-pan shaped flange connections. In addition, a method how to determine the bolt preload taking into account the allowable amount of the leakage was demonstrated. Furthermore, discussion was made on the effect of the bolt pitch on the sealing performance.

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This paper presents a numerical solution to a non-parametric shape optimization problem for design of suspension arm in which strength of suspension arm is evaluated by reaction force to plastic buckling load due to compulsory displacement. To deal with buckling phenomena, the geometrical non-linearity and material non-linearity are considered. Hyper-elastic theory is applied to calculate the deformation of suspension arm, under assumption of monotonous loading. Mass and the reaction force integral to the buckling phenomena are chosen as an objective function and a constraint function, respectively. The shape derivatives of these functions are evaluated by the shape optimization theory. A numerical scheme based on a sequential quadratic approximation method is applied to reshape by using the shape gradients. In this scheme, the traction method is used to find the decent directions of the cost functions. The scheme is implemented by using a commercial shape optimization program. In this program, the shape gradients are calculated by a user sub-program which is developed by using the result of non-linear FEM analysis of a commercial solver. The numerical example for a suspension arm model shows 12% of mass reduction while keeping the reaction force integral constant.

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In the authors' previous studies, the theoretical model of ultrasonic wave velocity propagating in plastically deformed solids has been proposed by one of the authors and successively verified experimentally. Then, deformation localization was analyzed by adopting the proposed theoretical model. The onset of localization of plastic deformation has been defined as the occurrence of “stationary discontinuity” characterized by a vanishing velocity of an acceleration wave based on acceleration wave theory. Moreover, based on shock wave theory one of the authors derived that the micro-crack nucleation is caused by the jump of the velocity along the intersected crossing line between two different stationary discontinuity bands characterized by vanishing velocity of an acceleration wave. In the previous paper, to consider dependence of the progress of ductile fracture of crystal solids on crystal orientations the algorithm of acoustic tensors derived from the proposed model was built into finite element crystal plasticity model (FEPM) and the progress of ductile fracture in FCC single crystals was analyzed. In this paper, dependence of the ductile fracture progress in FCC bi-crystal models on combinations of crystal orientations is examined.

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In this paper, we propose an orthotropic hyperelastic model for the fiber-reinforced rubber material used as rubber seals in electric generators. The fiber-reinforced rubber is composed of rubber matrix material that is reinforced by two families of fibers. The mechanical properties is anisotropic on directions of two fiber families. We improve an anisotropic model by adding terms to the strain energy function to consider its mechanical properties in small deformation region. The energy functions of the fiber families was represented by power series of invariants of stretch and shear deformation in fiber families. Moreover, the proposed strain energy function was polyconvex in totality. In order to identify material parameter of the proposed model, biaxial tensile test result of the rubber matrix and uniaxial tensile test result of the fiber-reinforced rubber were approximated by the nonlinear least squares method. Finally, applicability to the fiber-reinforced rubber of proposed model by FEM simulation of tensile, shear and compression was demonstrated to evaluate the applicability of the proposed model to the rubber seal.

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Extruded magnesium alloy shows a strong anisotropy of mechanical properties, which is caused by both of a crystallographic nature in hexagonal close packed lattice structure and a fiber texture with basal plane aligned parallel to the extruded direction by mechanical processing. To evaluate fatigue deformation behavior and fatigue life of extruded magnesium alloys, total strain-controlled and stress-controlled low-cycle fatigue test of three extruded magnesium alloys, AZ31, AZ61 and AZ80, were performed in ambient atmosphere at room temperature using smooth round bar specimen. Mean tensile stress during the total strain-controlled fatigue process and mean compressive strain during the stress-controlled fatigue process appeared due to the difference between tensile yield stress and compressive one, which resulted in mechanical twinning in the compressive phase. Fatigue criteria proposed previously considering the mean stress effect were evaluated in terms of fatigue life predictions based on the experimental results. Also, an energy-based model taken into account of plastic and elastic energy density was discussed to predict the fatigue lives obtained from the total strain- and the stress-controlled fatigue experiments.

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In this paper, time-dependent dimensional change in a symmetrical cross-ply laminates was predicted by transverse properties of the CFRP laminates. CFRP with pitch-based carbon fiber and cyanate ester resin was chosen for the study. Viscoelastic property was obtained by performing tensile creep test for unidirectional laminates in the transverse direction. In addition, shrinkage caused by physical aging was obtained by measuring the strain change for unidirectional laminates as well. Experimental results were applied to the classical lamination theory in order to predict the time-dependent dimensional change of a symmetrical cross-ply laminates. The strain change in a symmetrical cross-ply laminates was obtained experimentally using an extensometer, and the result was compared with the prediction. From the comparison, it was concluded that the proposed prediction method is appropriate. It was also found that physical aging shrinkage must be compensated in order to evaluate the relaxation modulus from tensile creep test result. The effect of physical aging shrinkage must also be considered in prediction of time-dependent deformation in cross-ply laminates.

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The fracture splitting method of the connecting rod production has been developed since about 20 years ago. We examined the mechanism of the fracture to improve the accuracy of the fracture splitting of the surface of the big end of the connecting rod, using the test specimens which were simulating the big end of the connecting rod, and made of the same kind of material, S50C quenched and tempered steel. On the bore of the test specimen a V- notch was fabricated with two kinds of methods, the machining and laser processing. Then applying the tensile load on the specimen, the crack growth phenomenon was measured by using ultrasonic surface wave. As a result, significant differences were not observed in the crack growth phenomenon between the two test specimens. The crack initiation loads were 72-75% against the fracture loads. On the fractured surfaces of the both kind of test specimens, similar ductile and brittle fracture surfaces were recognized. The ductile fracture surface appears when the crack velocity was slow, and was accompanied by transformation. It can be proposed that the actual mass production jig systems should have the movement system that would be able to apply a big rupturing load rapidly, after keeping the full preload before the crack initiation.

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Influence of interlayer thickness on singular stress fields around vertexes in 3-layered 3D-joints is evaluated through eigen analysis and BEM using fundamental solutions for two-phase materials. A model for analysis is three-layered joints consisting of Si, resin and FR-4.5. A relationship between singular stress fields and the resin thickness is precisely investigated. All stress components are expressed as spherical coordinate systems in which their origins are located at the vertex of each interface. They are derived from the transformation of coordinate system; from x-, y- and z-coordinates to r-, θ- and φ-coordinates. Here, θ is the angle from z-axis, φ is the angle from side surface and r is the distance from the stress singularity point. Angle, θ_max, for the maximum of stress, σ_θθ, near the vertex of the interface is firstly searched for various angle φ. A coefficient of the power-law term in the expression of stress distribution for the r-direction is determined for the stress distributions in the θ_max direction. The coefficient is referred to as the intensity of singularity in the r-direction. The intensity of singularity increases with the resin thickness, and attains to an upper limit in the case where the resin thickness is larger than the width of the model. Intensity of singularity in the φ-direction along θ_max direction is also investigated. Values of the intensity of singularity in the φ-direction are a constant for Si-resin and resin-FR4.5 interfaces. Three-dimensional intensity of singularity at the vertex in three-dimensional joints is defined considering the intensities of singularity for the r- and φ-directions. Variation of the three-dimensional intensity of singularity at the vertex with the resin thickness is similar to that of the intensity of singularity for the interface.

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The constitutive equation based on the concept of continuum damage mechanics is formulated for the gray cast iron as used in diesel engine parts, assuming it as an elastic damage viscoplastic solid. The microscopic stress and strain evaluation is simplified in the two-scale model for the damage evolution. Lots of material parameters in the constitutive equation are determined by using the uniaxial tensile/compressive and the fatigue test results. The local approach to fracture analysis (the uncoupled analysis) for the fatigue tests of notched circular bars is conducted by using the identified constitutive equation model and the commercial three-dimensional finite element program. The validity of the proposed model is illustrated by comparing the calculated results with the experimental results. It is expected that the developed computational modeling can be used effectively to predict the fatigue life of gray cast iron machine parts.

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We investigated the mechanical properties of graphene or graphite containing cluster-type vacancies or two single vacancies under tensile loading using molecular dynamics (MD) simulation. In the MD simulation, two types of potentials were used: the second-generational REBO potential for covalent bond and the Lennard-Jones potential for the interlayer interaction of graphite. We found that the tensile strength drastically decreases with increasing the size of vacancies, while the Young's modulus hardly changes. We also found that the slip deformation occurs in graphene containing vacancies under Zigzag tension, while that doesn't occur in pristine graphene until just before fracture. In addition, it was found that the tensile strength of graphene is affected by the slip deformation rather than by the distance between two single vacancies which are distributed in the loading direction or its traverse direction. Our results show that the displacements of atoms around the vacancy become a trigger that causes the slip deformation.

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When a local compression load is vertically applied on a face sheet of Honeycomb core sandwich panel (hereafter, HSP for brevity), a dent will be formed at relatively low force. Therefore, local compression tests of HSPs with different core height were carried out for a peripherally clamped specimen and a bottom face fixed specimen. From obtained results, the follows were summarized: 1) There was no effect of core height on strength. 2) Two peaks on load — displacement curve appeared for the peripherally clamped specimen. But, one peak appeared for a bottom face fixed specimen. 3) A peak load at first time for a peripherally clamped specimen was least for all. A peak load at second time for a peripherally clamped specimen was higher than that for a bottom face fixed specimen. 4) An Energy absorption for a peripherally clamped specimen was superior to that for a bottom face fixed specimen, because of a deflection observed for the only peripherally clamped specimen.

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A crystal lattice in a metal during recrystallization process is modeled as an elastic bar element subject only to stretch and its kinematics is discussed. The balance laws of mass, momentum, angular momentum and energy of the lattice element are formulated. These laws are summed up over a phase in a representative volume element (RVE) and averaged in the RVE so as to prepare to develop macroscopic balance laws for a continuum mixture consisting of several phases. When the RVE converges on a material point at the final procedure of formulation, the present model can be regarded as a director model whose direction vector expressing the crystal orientation is attached to a material point of simple body. During the averaging process, two useful theorems are proposed for averaging terms associated with mass source and then these theorems are verified. Moreover, defining the representative lengths both in macroscopic and microscopic scales and performing an order-estimation for the balance law of angular momentum, this law can be separated into the bulk and lattice parts. The former results in the usual form, so that the Cauchy stress keeps symmetric even though the spin angular momentum of crystal lattice is taken into account. On the other hand, the latter corresponds to the evolution equation of crystal orientation of KWC type phase-field model.

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Multi-phase-field (MPF) method which is capable of using several phase-field variables is applied to simulate martensitic transition in micro-scale Ni-Ti shape-memory alloy (SMA). By modeling Ni-Ti SMA specimen in MPF simulation assuming only three major variants of martensite crystal in monoclinic structure, the detailed manner of forming martensite variants and interaction between them are observed. We adjust several free energy (densities) usually used for the phase-field functional to Ni-Ti SMA properties, e.g. chemical free energy, elastic strain energy, gradient energy, and double-well potential energy. Especially in the formulation of elastic strain energy, to express austenite (cubic)-to-martensite (monoclinic) transition of Ni-Ti alloy, microscopic parameter available from experimental result for lattice mismatch between austenite and martensite is brought into free energy functional. We discuss the different growth of martensite variants depending on initial condition for martensite nucleus, in which some arbitrary area in the computation domain is provided with random number. It is confirmed that a martensite variant with a positive lattice mismatch (i.e. the direction of larger edge in monoclinic unit) grows preferentially in the case of tensile loading in that direction. In compression, a variant with the most negative mismatch in the compressive direction grows strongly. The starting time of loading is sometimes a factor for the resulted variant structures. We found that, once a lamellae structure is formed, the relation between direction of further loading and that of lamellae interface plane dominates the resulted structural combination of variants.

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This study investigated effect of titanium-fine-particle bombarding (Ti-FPB) treatment on corrosion resistance of A7075-T6 aluminum alloy and S45C carbon steel. Ti-FPB treatment is a surface-modification method to bombard countless titanium-fine-particles accelerated to high speed to the materials. After the treatment was conducted on the materials, the characteristics of the formed surface layers were examined in detail. As a result, it was shown that titanium composing the fine-particles was diffused over the surfaces because kinetic energy of the fine-particles was converted to thermal energy and the surface temperature was rapidly increased. At the same time, the surface hardness was remarkably increased and compressive residual stress was introduced. Further, the Ti-FPBed materials were immersed in 5 mass% salt-water maintained at 353 K. In this test, the specimens were fixed under stress of 80% of the yield strength. The results showed that the diffused titanium through Ti-FPB treatment improved the corrosion resistance of A7075-T6 alloy and S45C steel and the reduction in the tensile strength and elongation was suppressed.

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This study investigated damage condition of the large GFRP scrubber which was used to cleanse acid-gas for 35 years without large maintenance. Samples were obtained from four typical parts of the scrubber and optically observed on the inside surfaces and the cross-sections in detail. Ultrasonic-echo inspection and bending tests were further carried out for the obtained samples. The results showed that fishnet-like cracks were formed on the inside surface of the scrubber. Since acid-gas or clearing fluid invaded the inside of GFRP through the fishnet-like cracks, the damage such as delamination was induced in the chopped strand mats existing under the surfacing mats. However, the bending strength of each part was suitably maintained because the damage was generated in limited area. Furthermore, a relatively clear relationship was found between the ultrasonic-echo data and the residual bending strength. This result suggested the possibility of practical application of the ultrasonic-echo inspection for GFRP products.

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Dynamic tensile properties of a variety of plastics, were studied over a wide range of strain rates from 10^-2 s^-1 to 10³ s^-1 by using the Sensing Block Type High Speed Material Testing System (SBTS). The plastics were composed of seven kinds of polycarbonate, eight kinds of polyamide, one kind of polypropylene and acrylic-butadiene-styrene (ABS). It was observed for all the tested plastics, that the flow stress at each plastic strain increased monotonically with the logarithmic strain rate, and also increased linearly over the strain rates from 0.01s^-1 to 32 s^-1. It was observed that the strain rate sensitivity of the flow stress of these plastics decreased monotonously with the enhanced quasi-static flow stress. These phenomena are similar to those observed frequently for many metallic materials. The plastics were classified tentatively into three groups based on the rate sensitive characteristics. The possibility of expressing these dynamic properties for each group by using Tanimura-Mimura model was discussed.

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For the commercialization of solid oxide fuel cell (SOFC), in addition to the electrochemical reliability, it is also important to ensure the mechanical reliability of SOFC. Thus, the establishment of a suitable mechanical testing method under various temperatures and oxygen partial pressure conditions is a prerequisite for the development of reliable SOFCs. In this study, the in-situ mechanical testing method was developed in order to investigate mechanical property (i.e.: Elastic modulus and Fracture strength, Creep and Fatigue property) of solid oxide fuel cells components under high oxidizing/reducing environments. And mechanical property of gadolinium doped ceria (Gd_0.1Ce_0.9O_2-δ ; GDC) as oxygen non-stoichiometric compounds were evaluated in oxygen partial pressures under reducing conditions by developed In-situ mechanical testing machine. The experimental results of the investigation of elastic modulus and fracture strength on the SOFC components, the fracture stress of GDC were almost constant regardless of oxygen partial pressure, while elastic modulus decreased with decreasing oxygen partial pressure in reducing atmospheres. Mechanical properties of SOFC materials should be characterized by in-situ method because these results are different to quench method.

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In this study, the effect of a hybrid surface modification process; combination of fine particle peening (FPP) and plasma nitriding, on microstructure of pure iron was investigated. Surface microstructures of plasma nitrided specimens pre-treated with FPP were characterized by Optical microscopy, Scanning electron microscopy (SEM), Energy dispersive X-ray spectrometer (EDX), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). It was clarified that the nitrided layer of the hybrid surface treated specimen was thicker than that of the nitrided one. This was because the fine grains created by FPP facilitated the nitrogen diffusion during the following nitriding process. However, no noticeable differences were observed in crystal structure of the compound layer between hybrid surface treated specimen and nitrided specimen. In order to change the crystal structure of the compound layer, FPP was performed using a chromium particle; has a strong affinity for nitrogen, prior to nitriding. The results showed that chromium nitride was generated on the treated surface during the nitriding. These results mean that the proposed hybrid surface modification process is possible to shorten the nitriding time and to change the structure of the compound layer.

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This study aims to develop the manufacturing method of micro-structured parts by the metal powder injection molding (MIM) inserted micro-sacrificial plastic molds which were prepared by nano-imprint lithography (NIL) technique. In this process named NIL/μ-SPiMIM, the feedstock composed of nano-sized copper powder and polyacetal-based binder was adequately prepared and molded into polymethylmethacrylate films with fine line-scan structures, and the molded parts were sintered in a reductive gas atmosphere followed by solvent debinding of the films. The behavior in debinding and sintering was investigated by thermo-gravimetric analysis, carbon and oxygen analysis and SEM observation. The effects of sintering temperature on sintered density, shrinkage, and profile accuracy were evaluated systematically. It can be concluded that the manufacturing method named NIL/μ-SPiMIM proposed in this study has great potential to produce precisely 3 dimensional complex metallic parts with fine micro-structures.

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Magnesium has the smallest specific gravity in the structural metallic material applied to automotive parts. It is expected to be suitable light material to meet the needs of a vehicle weight reduction in recent years. However, magnesium alloy has low forgeability due to its crystal structure and low mechanical property at temperature over 373K compared with aluminum alloys. Therefore, magnesium application for automotive power-train part is quite few. On the other hand, Al-Ca series magnesium alloy has been developed by some researchers as low cost and heat resistant alloy. In addition, authors have developed the cast-forge process with semi solid injection molding process to improve the forgeability. The purpose of this research is to validate the feasibility of cast-forge process of Al-Ca series magnesium alloy applying the semi solid injection molding for preforming. Accordingly in this research, semi solid injection molded 4 mass%Al - 3mass%Ca magnesium alloy has been chosen because of a good heat resistant properties, and its forgeability and mechanical properties after forging has been studied. As a result, it is proved that 4 mass%Al-3mass%Ca magnesium alloy shows excellent forgeabilty and heat resistant compared to conventional magnesium alloys. It is expected that applying this new alloy to cast - forge process with semi solid injection molding and forging realizes low cost manufacturing process for automotive magnesium parts.

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Steel conveying rollers used in hot rolling mills must be exchanged frequently at great cost because hot conveyed strips induce wear and deterioration on the surface of roller in short periods. In this study, new roller structure is considered which has a ceramics sleeve connected with two steel shafts at both ends by shrink fitting. Here, although the ceramics sleeve can be used for many years, the steel shaft sometimes has to be exchanged for reconstruction under corrosive action induced by water cooling system. Since the thermal expansion coefficient of steel is about five times larger than that of ceramics, it is necessary to investigate how to separate the shrink fitting system by heating outside of sleeve and cooling inside of the shaft. In this study, the finite element method is applied to analyze the separation mechanism by varying the geometrical and thermal conditions for the structure. Finally the most appropriate dimension and thermal conditions have been found, which may be useful for designing of new rollers.

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The basket of transport and storage cask must have not only a structural strength during transport and storage conditions, but also heat removal function. The basket material is also preferable to be light in order to reduce the weight of cask because it is very important to increase the number of fuel assemblies loaded in the cask for efficient transport and storage. Especially, aluminum alloy is a suitable base material for the basket due to its low density and high thermal conductivity. In order to use this material for cask basket, it is necessary to be registered to the “Rules on Transport / Storage Packagings for Spent Nuclear Fuel (JSME S FA1-2007)” by the Japanese Society of Mechanical Engineers. Therefore, various mechanical properties such as tensile strength at elevated temperature with or without long term aging and creep properties, etc.. And the allowable stresses of A5083FH-O have been evaluated according to the “Rules on Transport / Storage Packagings for Spent Nuclear Fuel (JSME S FA1-2007)”.

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