We have been so far analyzed several three-dimensional joints using BEM and FEM. However, many unsolved problems in three-dimensional joints exist untill now. In this study, on the basis of FEM using an interpolation function considering a stress singularity field near the vertex of three-dimensional joints, an eigen equation was derived for determining the order of stress singularity. Four typical models of joints are analyzed in our calculations. Model 1 is a typical joint of three-dimensional joints which is composed of two blocks with different properties. Model 2 is a joint which a 1/8 elastic material bonds to a 1/4 elastic material so that a free surface in the 1/8 material coincides with a free surface in the 1/8 elastic material. Model 3 and model 4 are joints which a block of material 1 is embedded into material 2. In model 4, an interface in three interfaces for material 1 surrounding a vertex disbonds from material 2. An accuracy of calculation is examined by varying the mesh size and the number of gaussian integration points in model 1. Contour map of the order of stress singularity is mapped on Dundurs' parameter plane in model 2, model 3 and model 4. The distributions of displacement and stress near a vertex were precisely investigated determining the eigen vector of the eigen equation in model 3 and model 4. The characteristics of displacement and stress can be expressed by a sum of series of the product of the λth power of distance from the vertex and the distribution functions of intensity.

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Multiscale Modeling for heterogeneous media such as fiber or particulate reinforced composite materials and porous materials is one of the recent topics in computational mechanics and materials science. Homogenization technique has been studied and used for the micro-macro bridging under the conditions of periodicity of the microstructures and of uniformity of macroscopic field. However, these two conditions make the evaluation of microscopic stresses using the homogenized model useless in the real applications, because the stresses with high gradient at the interface, edge or surface as well as the stress concentration due to voids etc. must be calculated. To solve this problem, in this paper, the finite element mesh superposition method is employed to calculate the microscopic stresses directly for local heterogeneity without the periodicity under non-uniform macroscopic strain field. Through two numerical examples, the efficiency of the modeling and the effectiveness of the microscopic stress evaluation are discussed.

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This paper presents a shape optimization method to displacement path control problem taking into account geometrical non-linerity. The aim in this paper is to minimize the time integration of squared displacement error norm on the responded mode and the prescribed mode by varying a boundary shape under a volume constraint. The shape sensitivity is derived using the Lagrange multiplier method and the formula of the material derivative. A procedure to solve this problem using the traction method is presented, which one of the authors has proposed as an approach to solving domain optimization problems. The validity of proposed method is verified by applying to basic numerical examples.

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In this paper, we analyze the microscopic symmetric bifurcation buckling of cellular solids subjected to macroscopically uniform compression. To this end, showing the principle of virtual work for periodic solids in the updated Lagrangian form, we build a homogenization theory of finite deformation, which satisfies the principle of material objectivity. Then, we state the following postulate : At a microscopic symmetric bifurcation point, microscopic displacement rate gets spontaneous, but changing the sign of the spontaneous displacement rate field has no influence on the variation of macroscopic states. By applying this postulate to the homogenization theory, we derive the conditions to be satisfied at the bifurcation point. The resulting conditions are discretized using a finite element method in order to employ the present theory in computational analysis. The finite element discretization also deals with a general case, which includes microscopic non-symmetric bifurcation as well as symmetric one.

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Molecular dynamics simulation is carried out to investigate the anisotropy of heat conduction in fcc crystal. Here the heat is forced to flow into four different directions ; <100>, <110>, <12^^-1>and <111>by arranging the unit cells in corresponding directions, while atoms are disposed on the lattice point of fcc crystal. Lennard-Jones potential function is employed and periodic boundary conditions are imposed on all directions. A certain amount of energy is supplied to the central region and temperature on the side regions are kept constant. After a period in equilibrium state, heat supplied at the central region flows continuously to the side region. Then the thermal conductivity is evaluated by two ways: one is based on conventional Fourier's law and the other is energy transportation per atom. As a result, <111>, <12^^-1>, <110> and <100> directions are revealed to have the higher heat conductivity in this sequence. One of the factors affecting the anisotropy is explained by interatomic correlation function of heat flow per atom.

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The previous paper on the deformation behavior of the diamond-like carbon (DLC) pointed out the following two things. One is that the content rate of sp³ bonded atom in the initial atomic model was much less than the experimental results. And the other is that the Tersoff type interatomic potential employed in the previous molecular dynamics simulations never resists the torsional deformation. It may be fatal defect when considering the deformation of the amorphous-like imhomogeneous structure. In the present paper, Order (N) tight-binding molecular dynamics scheme (O(N)TB-MD) is applied to elucidate these problems. First, we demonstrate that an environment dependent TB potential proposed by Wang and et al.is applicable to the DLC containing the various crystal structures with different binding energies. Moreover, the density matrix method as an Order (N) scaling is adopted to reduce the drastic computational time with keeping the reasonable accuracy of an interatomic force as the first-order gradient of the potential energy and elastic stiffness as the second-order gradient. It is found that the high content of sp³ in the initial DLC model by quenching process is obtained, which is in good agreement with the experimental results. And the torsional resistance plays an important role in the deformation of the DLC film.

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In order to estimate the accuracy of multiscale analysis for materials with microstructures based on the eigenstrain fields formulated by Nemat-Nasser and co-workers, we performed the computational simulation employed the piecewise approximation method, so called Subdivisions Method that discretizies inclusion region into the sub-domains where the eignenstrains are taken as constant. Through the numerical evaluation of the overall properties and microscopic deformation behavior of elastic solids that contain periodically distributed hard inclusions in soft matrix, we found that the results significantly depend on the way of discretization of inclusion into subregion. The results of Subdivisions Method with subregions that have the same volume show the excellent agreement with those due to Homogenization Method, whereas, those with the different volume were very poor. Therefore, it has been concluded that Subdivisions Method with the same volume of subregion provide efficient tool for the estimation of the macroscopic mechanical properties of the materials with periodic microstructures. The Subdivisions Method with the same volume of subregion is applied to investigate the overall complex properties and microstrain of unidirectional/short-fiber reinforced composite materials and the effect of the location of reinforcements under a constant volume fraction on its macroscopic mechanical properties are clarified.

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This paper is concerned with the theoretical treatment of transient thermal stress problem involving a cross-ply laminated cylindrical panel consisting of an orthogonal pile of layers having orthotropic material properties due to nonuniform heat supply in the circumferential direction. We obtain the exact solution for the two-dimensional temperature change in a transient state, and thermal stresses of a simple supported cylindrical panel under the state of plane strain. As an example, numerical calculations are carried out for a 3-layered cross-ply cylindrical panel, and some numerical results for the temperature change, the displacement and the stress distributions are shown in figures.

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This paper deals with the two-dimensional generalized thermoelasticity based on the Lord and Shulman's theory and the Green and Lindsay's theory by use of the state space approach. The fundamental equations of generalized thermoelasticity, which include both generalized theories, are used. The generalized thermoelastic problem for a layered medium, which consists of homogeneous and isotropic layers and whose surface is traction free and subjected to a partial heating, is analyzed by means of the Laplace and Fourier transforms. The inversions of the Laplace and Fourier transforms are carried out numerically. The numerical calculations for temperature and stresses based on the Lord-Shulman's theory are carried out.

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This work considers the two-dimensional thermoelastic problem in an infinitely long cylinder with free surface subjected to an asymmetrically instantaneous heating on the basis of the generalized thermoelastic theories, i. e. the Lord-Shulman (L-S) and the Green-Lindsay (G-L) theories. The combined forms of the governing equations of both theories are used. The solution in the Laplace transform domain is derived analytically. Using the numerical inversion of Laplace transform has made it possible to obtain the two-dimensional thermal stress and temperature in physical domain for all time scales. Calculations have been performed on the basis of the L-S theory. The behavior of the thermal stress wave is exhibited. The effects of the relaxation time and the thermomechanical coupling on the thermal stress are discussed.

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The three kinds of fracture specimens are tested under different constraint conditions. One is 3PB (3 Point Bending) specimen, another is CCT (Center Cracked Tension) specimen, and the third one is called CCB (Center Cracked Bending) specimen. By the SEM (Scanning Electron Microscope) observation, it is shown that the roughness of fracture surface is different from each other largely. The number of large voids and the average diameter of them are also different from each other. They are the effect of constraint condition. The dimple fracture process is simulated by the finite element method. By the finite element analyses, the crack tip stress fields are obtained. The distribution pattern of the high stress triaxiality area corresponds to the fracture surface roughness qualitatively. The fracture pattern near the initial crack tip also agrees with the experimental data.

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In the case of plane strain plastic compression, behavior of a viscous lubricating oil trapped in a small pit on a contact surface is calculated by a finite element method. The oil pressure is controlled by the yielding condition. When the oil pressure is constant over the surface, the oil does not flow and the pit is not flattened. When the lateral deformation of material is constrained and pressure gradient is produced, the oil in the pit flows out and the pit is flattened. Reduction in heigth required to flatten the pit is above several times of the pit depth. A decrease in the viscosity and an increase in the pit depth enhance the flattening. When the compression tool is slid with a high speed, a hydrodynamic effect of the oil causes a pressure change and the pit moves in the sliding direction.

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To clarify the mechanism and mechanics of dislocation nucleation and motion in the atomic scale, a molecular dynamics simulation of tension along [001] direction is conducted on a nanoscopic specimen of single crystalline nickel. After showing perfect elastic behavior, the specimen plastically deforms at the applied strain of 0.084 by the passage of partial dislocations nucleated at the surface of the specimen. Detail observation of the dynamic process of a dislocation nucleation reveals that two successive instable behaviors of local lattices take place at the nucleation site in the homogeneously deformed body. The first instable behavior is the collapse of local lattices in the transverse direction to bring about the deformation concentration at the nucleation site. The second is the instable shear of local lattices on a slip plane in the deformation concentrated area. The nucleation and glide of a partial dislocation is recognized as the migration of atoms on the slip plane as the result of these instable behaviors. In order to elucidate the onset condition of the instable behaviors of local lattices, the positive definiteness of the elastic stiffiness coefficients, B_ijkl, of all local lattices are investigated. That is, the instability criterion proposed by Wang and Yip is adopted to the evaluation of the local instability. The results show that the minor determinants of B_ijkl related with the compliances of lattice for the transverse collapse and the slip deformation become negative at the onset of each instable behavior. Thus, the local lattice instabilities bring about the dislocation nucleation and motion and can be clarified by the negative definiteness of local B_ijkl.

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The effect of crystal grain size on the stress corrosion cracking (SCC) of a high-strength aluminum alloy 7475-T 6 sheet has been investigated using two types of tensile specimens with and without pre-crack, exposed in 3.5% sodium chloride solution. Little differences in the tensile property and fracture toughness are exhibited in the three materials A, B and C, having a fine-, medium- and coarse-grain size, respectively. The SCC rupture time of the smooth specimen is prolonged with the increase in grain size, namely in the order of material A<B<C. The resistance to SCC initiation and propagation of the pre-cracked specimen is also enhanced with the increase in grain size. Based on the test results together with the elasto-plastic FEM stress analysis, the threshold stress intensity K_ISCC of SCC initiation is derived to be in agreement with the K_I condition under that the plastic zone size R_p=(K_I/σ_ys)²/π in front of crack tip expands to a width of grain diameter, where σ_ys is the yield strength. Thus it is supported that the SCC process of the alloy 7475-T 6 is controlled by hydrogen embrittlement achieved over a critical distance corresponding to one grain size.

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To evaluate the biodegradability of polycaprolactone (PCL) 50 vol%Cu composites produced by the mechanical alloying (MA) method, degradation tests by lipase have been performed for some mechanical alloying time of the composites. As the results, total oxygen content and the weight decreasing rate caused by biodegradation have lower values at the long-time mechanical alloyed composites, while at the short-time mechanical alloyed composites have that of higher value. This results indicate that the biodegradability of the composites decrease with increasing the MA time. The cause of these results can be explained that the composites are not perfectly degraded, because it decomposes from the circumference of the metal powders aggregates at the short-time mechanical alloyed composites. On the other hand, the lower biodegradability in the long-time mechanical alloyed composites is probably caused by uniformity dispersion of copper powder in the PCL, because biodegradation occur successively from the outer layer.

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The change of the dynamic viscoelaticity during the fatigue process and the fracture surface phases were investigated to the fatigue fracture mechanism of PC and PMMA at high temperature in this study. The results are following as : (1) For the dynamic viscoelaticity testing, PC is heat-resistant materials because the change of E' was little from low temperature to high temperature of 140°C, however, PMMA is a sensitive materials to the temperature change. (2) For the tensile testing, PMMA comparing with PC was very large on the initial elasticity and low strain stress companion to the increase of temperature, therefore, PC is a ductile materials and PMMA is a brittle materials. (3) PMMA was more than PC on the low fatigue life due to the increase in testing temperature. Because there was an angle between the load direction and the crack propagation, the ductile fracture of PC took place in the part section. There was no change for the fatigue life of PC on the increase in the stress amplitude. (4) The fatigue fracture mechanism of PC is the same as that of PMMA at each temperature. There are closely relationship with the fatigue process of E' and the change trend of tan δ as well as the characteristic of the fracture surface.

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The effect of LCP content on the microstructure and fatigue fracture property of PP/LCP blend materials with easily recycle was investigated in this study. The results are following as : (1) PP/LCP blend is an immiscible two-phase material. While LCP content was below 40%, it would be easily formed fiber. (2) Because the thermal expansion coefficient of PP is large, LCP is a nonexpansion material. Thus, the mechanics joining strength of the interphase between PP and LCP phase would be improved when the PP content was more than 60%. (3) According to the tensile testing results, PP was a ductile material, but LCP is a typical brittle material. For those blend materials companion with the increase in the addition content of LCP, the tensile strength was increased, but the stretch would largely decreased. (4) E´would decrease and tan δ would increase on the recycling fatigue of PP single phase, because the specimen producing heating itself happened ductile fracture. Companion to the increase in the addition content of LCP on the fatigue process, the trend degree of the decrease in E´and increase in tan δ would lower, the specimen lifetime would become larger, the fracture would also change to the brittle property.

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Rotating bending fatigue tests up to 10⁸ cycles were carried out in order to investigate the effects of double shot peeing using super-hard fine particles on the fatigue strength and the fracture mechanism in an 18%Ni maraging steel. The effects of surface roughness, residual stress and work hardened layer on the fatigue strength were examined in connection with the size of shot particles. The S-N curves of double shot peened specimens showed the same two steps as those seen in the S-N curves of single shot peened ones. The fatigue strength in the short life region is greatly increased by the double shot peeing irrespective of the size of shot particles, especially in the specimens with rough surface caused by the first stage of double shot peening. The high fatigue strength is due to very small surface roughness and high compressive residual stress generated just under the surface due to the second stage of double shot peening using super-hard fine particles. On the other hand, the fracture mechanism in the double shot peened specimens is just the same as that in the single shot peened specimens, i. e., in the short life region, surface fracture occurs, while in the long life region, fish-eye fracture, a typical interior fracture happens. As a matter of course, the fracture mechanisms can transit from surface fracture to interior fracture depending on the stress applied. However, at the stress levels between surface fracture and interior one, a unique interior fracture with the initiation site in the weak structure like a grain boundary was observed. This fracture surface showed a radial and rough one instead of the typical fish-eye surface which showed a flat surface.

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This study is conducted to clarify the relationship between the fatigue strength of nitrided titanium and that of the substrate. The result shows that the fatigue strength of nitrided pure titanium is improved by the increase in the fatigue strength of its substrate. It can be considered that this improvement is caused by the reduction in the magnitude of the stress field which is generated in the compound-layer by the slip of the substrate. However, the above improvement is limited in case of nitrided titanium alloys which have high strength such as nitrided Ti-6 Al-4 V and SP-700 alloys. That is because the compound-layer is subjected to the additional intensive tensile stress induced by the difference of Young's moduli between the layer and the substrate.

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Rotating bending fatigue tests were carried out to investigate the influence of shot peening on the fatigue strength of squeeze cast Al alloy AC4CH, and the results were compared with those of wrought Al alloy 6061-T6. The fatigue strength increased by shot peening in both materials and the increase in the fatigue strength is larger in the wrought Al alloy than in the cast Al alloy. In shot peened materials, a crack initiation and its early growth process is accelerated by the stress concentration due to surface roughness and the damage, and the growth of a small crack is suppressed by the work hardening and the compressive residual stress.

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The purpose of the present study is to investigate the unique slip behavior near the interface boundary (IB) in the high cycle fatigue. Push-pull fatigue tests were carried out for two-phase (α/γ) stainless steel bicrystal, which consists of ferritic (Fe 30 Cr) and austenitic (FellCr 19 Ni) single crystals. In the tests, the unique slip, which is not expected from the crystal orientation, was observed in the γ-phase near the IB. The analysis of finite element method reveals that the slip is caused by the increase of resolved shear stress, τ_rss, due to the constraint of deformation at the IB.

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A new film fatigue testing method was proposed by which fatigue cracks can be initiated and propagated in a film adhered to cover an elliptical through-hole in a base plate subjected to push-pull cyclic loads. Using this method, in order to discuss the effect of rolling texture on fatigue crack propagation properties of commercially-pure iron films with the thickness of 100 μm, the films were annealed at 873 K, 1 073 K and 1 173 K after rolling, and the two types of specimen whose rolling direction was either parallel or perpendicular to loading direction were fatigued. The crystallographic characteristics of rolling textures in annealed iron films was analyzed using EBSD (Electron Backscatter Diffraction) system. As a result, the anisotropy of rolling texture remained after annealing, and there was a difference between the two types of specimen in crack morphology on the specimen surface. When compared at the same stress intensity factor range, ΔK_est, evaluated from the crack opening displacement, fatigue cracks in the film loaded to the perpendicular direction to the rolling direction propagate faster than that in the film loaded to the parallel direction. The reason was probably that the slip plane of the rolling texture in iron film materials is different in accordance with the relationship between rolling direction and crack propagation direction.

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Fatigue strength and fracture mechanism of a medium carbon steel (S35C) with gas flame thermally sprayed Co-based alloy coatings were investigated by rotating bending tests. After fusing treatment, machining was done to manufacture three kinds of specimens having 0.3 mm, 0.5 mm and 1.0 mm in coating thickness. The fatigue strength of all coated specimens was much higher than that of the substrate and that of the grit blasted ones. Especially, it was found that the fatigue strength of the specimens with 1.0 mm coating were higher remarkably compared to that of ones with 0.3 mm and 0.5 mm coatings. The result showed that at lower stress levels, the fatigue cracks were initiated inside the substrate of 0.3 mm and 0.5 mm coated specimens only (Internal failure in the substrate). At higher stress levels the fatigue cracks were initiated at the coating layer, which were originated from the porosity located in coating layer of all coated specimens (Surface failure in the coating layer). But no fracture mode transition was noticed for the case of 1.0 mm coated specimen. Discussion have been made on the cause of the fracture mode transition depending on the coating thickness on the basis of the results of the calculation of the stress at the location where the fatigue fracture was initiated.

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Japanese cedar is the most important conifer for reforestation in Japan. Recently, compression process upon lumbers are expected to be an effective way to progress the mechanical property and able to extend the uses of Japanese cedar. This study evaluated the static & dynamic bending strength of compressed Japanese cedar lumber (compressed lumber) and tried to progress the bending strength of Al alloy shape by compressed lumber as the reinforcement. As the results, bending strength of compressed lumbers are equal to the A class lumber used for structures by the regulation of JAS (Japanese Agricultural Standard). Bending strength of Al alloy shape can be progressed by compressed lumber.

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We present the method of constructing a pressure sensitive yield function which accounts for the porosity, incorporating the data from the compression of cylindrical metal powder assembles. The load paths consist of fluid hydrostatic pressure loading up to a set value, followed by the addition of an increasing mechanical axial load. The yield function (yield curve) for less than fully dense states is represented in the relation of deviatoric stress q to hydrostatic stress p. In powder metal assembles the curve which gives the relation between p and q at constant density has been frequently used as yield curve. However, it does not seem to have been examined experimentally whether the constant density curves are consistent with the yield curve. For the prediction of yield function two quantities are required, for example, axial stress and volumetric strain developing with an increasing axial strain. Here, the data obtained by Jin and Cristescu and by Gurson and McCabe are used. Our results indicate that several current models proposed for powder metal deformation do not represent actual constitutive behaviour under the assumption that associated flow rule is valid and yield curve expands in a similar shape with compressive deformation.

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Structural health monitoring is a noticeable technology for aged civil structures. The present paper proposes a new diagnostic tool for the structural health monitoring that employs a statistical diagnosis of self-learning method. Most of the structural health monitoring systems adopt parametric method based on modeling or non-parametric method such as artificial neural networks. The new statistic diagnosis method does not require the complicated modeling and a large number of data for the training of the artificial neural networks. In the present study, the proposed method is applied to detect pipe deflections due to plastic bending, which simulates disaster damage of gas pipes. Response surfaces among the measured natural frequencies of the pipes are produced at the initial stage and monitoring stages, and the difference of the response surfaces of the monitoring stages from the initial stage is statistically tested using F-test. As a result, the new method successfully diagnoses the damage without using modeling and a large number of data for training.

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