The molecular dynamics simulation has been widely applied to Si/SiO₂ systems, which are basic materials for the LSI technology. For the simulation, it is necessary to use accurate interatomic potential function, which reproduces the force acting on each atom. However, the validity of potential functions proposed has not been discussed in terms of the force. In this study, the force calculated by the Tersoff potential is compared with that obtained by an ab initio calculation in some snapshots of Si/SiO₂ systems at the temperature of 300K. It clarifies that the potential does not properly reproduce the force. Then, optimizing the parameters in the Tersoff potential on the basis of the force acting on each atom obtained by the ad initio calculation(Force matching method), two modified functions are proposed. One is"Potential A"obtained by optimizing the parameters for the Si crystal and the β-cristobalite SiO₂ crystal. The"Potential A"correctly reproduces not only the forces but also the lattice constants. The other in"Potential B"obtained by optimizing the parameters for a Si/SiO₂ interface model as well as the Si crystal and the β-cristobalite SO₂ crystal.The forces and lattice constants are successfully reproduced. Moreover, the"Potential B"gives a good result for the β-quartz SiO₂, which is not used for the optimization. This implies the versatility of the proposed function.

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In considering mechanical behavior of crystals, it is very important to know the elastic incompatible stresses near the dislocation which plays an important role elasto-plastic deformation. The authors proposed a finite element model of an edge dislocation, based on the mathematical model of dislocation. In this paper, a finite element model of an arbitrary inclined edge dislocation is proposed by the use of a dislocation of displacement, and the stresses around an edge dislocation in an infinite region are obtained and compared with exact solutions. In this analysis, opening mode dislocation of displacement and shear mode dislocation of displacement are located along the same line, and the corresponding nodal points are connected each other. Also, the problem with two edge dislocations is treated. The results coincide with exact ones.

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In this paper, we propose an algorithm of FEM for stress analysis of the materials which have viscoelastic viscoplastic chatacteristics such as UHMW-PE. The constitutive equations for plasticity and viscoelasticity derived from the experimental results were used in the algorithm. The new displacement meter made from eddy current sensors, which was made to obtain more accurate test data at low strains, and the constitutive equations derived from the experimental results by the meter were shown. Finally, the comparisons of the numerical results and the experimental results of the load vs. displacement curves for the specimens with side groove were performed. The calculated values were in good agreement with the experimental results. It was confirmed that the algorithm of FEM and the constitutive equations proposed by the authors were valid for stress analysis of nonlinear viscoelastic viscoplastic problems.

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This paper presents a shear deformable finite element method for the static analysis of composite laminated plates and shells. The finite element based on the Mindlin shear deformation theory of plates. The flat triangular shell element is formulated considering the anisotropic behavior of composite materials with the assumption that the out-of-plane shear strain is constant in two directions within an element. The element consists of three displacements and three rotations as the generalized degree-of-freedom per node. The validity of the present formulation is determined via problems for which the exact solutions and numerical results are available. Excellent accuracy and fast convergence are observed.

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In structural analysis it is often necessary to determine the geometrical properties of cross sectional areas. The location of the shear center is of greater importance for a thin-walled cross section.The purpose of this paper is the computation of the shear center of the arbitrary thin-walled cross sections using the finite element method. The coupling problem of shearing and torsional deformation of a thin-walled beams based on Saint Venant's theory is considered. This problem of coupled shearing and torsional deformation was analyzed using the finite element method in which the matrix of shear rigidity and torsional rigidity were determined. The shear center can be obtained determining the coordinate axes so as to eliminate the nondiagonal terms.

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The axial impact crushing behavior of a curved tube is studied by the finite element simulation, and effectiveness of stiffening at the curved parts and shape perturbation at two straight parts of tube are discussed. Based on the numerical analyses, maximization problem of dynamic crushing energy absorption of curved square tubes is solved by using the crashworthiness maximization technique for tubular structures which combined the techniques of design-of-experiment, response surface approximation as well as usual mathematical programming.

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This paper is concerned with the thermal and thermal stress waves in nonlinear elastic solids subjected to the impulsive heating. The formulation of the problem is based on the generalized theory of thermoelasticity proposed by Lord and Shulman. A set of generalized equation which governs the propagation of plane, cylindrical and spherical waves in nonlinear elastic solids is presented. The solutions are obtained by using the characteristic method. Numerical results for the propagation of thermal and thermal stress waves in nonlinear elastic plates are presented in the graphical form.

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For fundamental deformation of the case of the corrugated fiberboard box shape under uniform compression(1N/mm²), it was discussed that side plate deformation of its case was simulated as the zero displacement of the breadth direction on upper and lower edges. Then an elastic stress formulation, for their side plates(breadth L and height h)was expressed. Also, from this formulation, the stress analysis of its plate was performed and its characteristic behavior was done obviously. In the tange y=3h/8∼5h/8(y:diatance from the center in the height direction), the normal stress σ_x in the breadth direction for the plate decreases with the increases of distance(x-L/2)from the plate center in the breadth direction, and in the range y=3h/8∼5h/8, increases roughly. In y=h/2∼3h/4 range, absolute value σ_y of the normal stress in the height direction for the plate decrease roughly with the in crease of(x-L/2), and in range y>3h/4, the constant σ_y appears about the x=L/2. Also, in the range h/2<y&lnE;3h/4, the absolute shear stress t_xy increases initially and next decreases with the increase of(x-L/2), and in the range y>3h/4 becomes inversely.

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Dynamic creep test and its analysis were performed for Si-Ti-C-O Ceramic fiber bonded body under bend loading at 1400°C. Creep displacement under cyclic loading with mean stress σ_m1=196 MPa and stress amplitude σ_a=49 MPa is quite similar to the one under constant static load of σ₀=196 MPa, while the dynamic creep displacement under loading condition at σ_m1=245MPa and σ₌49 MPa is much larger than static creep displacement at σ₀=245MPa. SEM observations revealed that the failure of matrix material was caused around the neutral plane of the specimen by cyclic shear stressing in the dynamic creep process at σ_m1=245MPa and σ_a=49 MPa. Finite element method analysis was performed for the dynamic creep process, where the gradual attenuation of shear modulus G₁2 with progress of dynamic creep was assumed. The calculation described qualitatively well the dynamic creep deformation behavior of this material. The normal stress distribution of the specimen and the shear stress distribution in the neutral plane along the specimen axis were presented on the basis of the FEM calculation.

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The three-dimensional finite element analysis was carried out by using the compact normal and shear(CNS)specimen with various kinds of specimen size. The complex stress intensity factor K associated with an elastic interface crack was evaluated by the virtual crack extension method. The effect of Young's modulus and Poisson's ratio on stress intensity factors was discussed under various kinds of mixed-mode loading. It is predicted that the stress intensity factors would vary depending on the specimen size. Then, the size effect on stress-intensity factors was discussed. A simple evaluation method for stress intensity factors is needed in the fracture toughness test. Therefore, the polynomial fit is proposed to evaluate the stress intensity factors at the midsection of CNS specimen with an interface crack subjected to mixed mode loading. It is possible to evaluate the stress intensity factors of CNS specimen with high accuracy by the present polynomial eveluation.

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Rotating bending fatigue tests were performed for a high carbon-chromium steel in order to clarify the influence of radical nitriding on fatigue strength and fracture mechanism in the life region where a fish-eye fracture occurs. It was found that crack intiation originated from slips or surface defects under high stress levels and from internal defects under low stress levels in the both quenched and tempered steel and nitrided steel. However, fatigue life in the fish-eye fracture region was extremely shorter in the nitrided steel than in the quenched and tempered steel. Around the non-metallic inclusion of fish-eye, granular facets were observed in the quenched and tempered steel but in the nitrided steel featureless facets generated. Macroscopic examination of fish-eye fracture surfaces also showed that in the quenched and tempered steel, a crack propagated radically with a start at fish-eye, but in the nitrided steel it grew rapidly within diffusion layer and then extended internally from the whole diffusion layer to form a ring-shaped fracture surface.

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In spite of the tough pitch copper material is used for the many kinds of conductors of electrical machining devices, the fatigue phenomenon of the tough pitch copper material does not still clarify under variable stresses considering to a service loading. Then, constant stress amplitude fatigue tests were carried out for the tough pitch copper sheet material and then the fatigue life under variable stresses were predicted by Miner's law using constant stress tests results as shown S-Ndiagram. The program fatigue tests consist of two steps and multifold stress levels were carried out for tough pitch copper sheet specimens compared with the fatigue lives predicted by using Miner's law. As it was clear that the fatigue lives predicted by using Miner's law were shorter than the experimental program fatigue lives under variable stresses in service loading, so new practical diagram modified from original S-N diagram was proposed. The fatigue lives predicted by using new S-N diagram coincide with experimental fatigue lives under variable stress consist of two or three step and multifold stress levels.

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The effect of temperature on fatigue properties of a plain weave glass fabric reinforced plastics(GFRP)under tension/ torsion biaxial loading was studied. Fatigue tests were conducted at several terperatures between -23 and 60°C. The biaxial loads were proportinally applied to specimens. Although the static strength of GFRP at elevated terperature was lower than that at room and low terperatures below 0°C, the fatigue life at 60°C was longest when the specimens were subjected to a tension/torsion biaxial stress combination whose maximum cyclic stress normalized by the static strength at each temperature was constant for all tests.The primary fatigue damage at elevated temperature was meta-delamination occurring at cross-over points between wefts and warps. No meta-delamination was observed in the specimens tested at temperatures below 0°C while matrix cracks propagating across fiber bundles were formed. The modulus decay of GFRP in shear was greatly influenced by internal fatigue damage such as meta-delamination and matrix cracking more than the modulus decay in tension.

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The penetration of a viscous lubricant into a three dimensional surface crack under a rolling contact stress was calculated. The finite element method was applied to solve the Reynolds equation coupled with the elastic deformation of the crack. The process of penetration is roughly the same as the two dimensional model. The lubricant begin to flow into the crack when the contact pressure is passing the crack mouth. The lubricant enters to the crack tip and increases the stress intensity factor, when a nondimensional parameter β=ηυE²/(ap³₀)is small. The crack does not open when β is large, because the contact pressure has passed before the lubricant flows into the crack. The critical value of β was calculated. The penetration of the lubricant is not easy as compared with the two dimensional model.

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A macrocrack in a brittle material containing a cluster of microcracks experiences the stress shielding effect when the macrocrack front locates in the domain of stress relaxation induced by the microcacks. This is called the microcrack toughening effect for the macrocrack in a brittle material such as ceramic. Therefore the existence of microcracks improves the fracture toughness of the macrocracked solid. This paper presents the numerical analyses for the macrocrack in an anisotropically damaged materials. The homogenization method based on the superposition method is used to evaluate the material properties of the damaged materials and the mechanical behavior of the macrocrack in the damaged materials. In order to evaluate the mixed-mode stress intensity factors of a macrocrack in the anisotropically damaged materials, we derive the component separation method based on three dimensional path independent J integral. This paper provides the numerical results for the effective elastic moduli of the damaged materials and for the J integrals and the stress intensity factors of the macrocrack.

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A new method using energy release elements(EREs)for evaluating adhesive strength, which we suggested in our previous paper, is used to estimate debonding temperature of joints made from resin and steel. This estimated temperature agrees well enough for practical use with those measured by Terasaki et al. over all sizes and shapes of test specimens. This agreement shows that the new method can be widely applied for estimating adhesive strength. When joint components are thicker than 2 mm and bonding angle is greater than 90 degrees, detail of the stress-deformation relation of ERE does not affect the estimation of debonding temperature. And different ERE characteristics determined by using one experimental datum give almost the same estimated temperature. These estimated temperature agree with those measured to the same extent as those estimated by Terasaki et al. by using energy release rate g as an evaluating parameter.

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Many of the ceramic coating material can be exposed to harsh working conditions because of their excellent characteristics. Therefore, for producing superior coating materials, it is necessary to establish a methodology for evaluating the mechanical properties of these materials. In the formedr report, nine kinds of TiN film 5μm thick, which were deposited on the different parent materials under different N₂ partial pressure were scratched and the relationship between the characteristics of the detected acoustic emission(AE)signals and the fracture modes of the film(i.e. cracking, chipping and flaking)was investigated. As the results, it was clarified that fractal dimension m determined AE peak amplitude distributions became grater than three when the fracture mode was cracking, the dimension became between one and three when the mode was chipping, and the dimension became less than one when the mode was flaking. However, it is necessary for evaluating the fracture mechanism to recognize the information on the changes of the fracture modes which is included in an AE event. In this report, wavelet transform(WT)was used to attain the subject. From the experimental results, it was found that the changes of the fracture mode are evaluated by observing the time-frequency analysis with WT.

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The great Hanshin-Awaji earthquake has brought a large number of structural failure and destruction. One of them is the fracture of a bridge bearing part of the Nielsen bridge type. It is not expectant that the fracture occurs under ordinary static or dynamic loading, instead the fracture is probably resulted from very high stress due to unexpected dynamic mechanism or impact. In this paper, the three dimensional dynamic behavior of a bridge of the Nielsen bridge type was analyzed, when an impact occurred between the upper and the lower parts of the bridge bearing of that, which might be caused by the great Hanshin-Awaji earthquake. The obtained numerical results show that a high stress sufficient to lead to a fracture occurs in the upper part of the bridge bearing, when an impact of velocity higher than 5m/s occurred between the upper and the lower parts of the bridge bearing.

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When a material is exposed to cavitation for a long time, the sueface is eroded like a sponge, which is one of the evidences of cavitation damage. However, the mechanism of the spongelike surface formation remains unclear. A magnesium oxide single crystal is useful to understand the fundamental mechanisms of cavitation erosion. In this study, magnesium oxide single crystal(100)surface were polished with four grades of emery paper to prepare test specimens. The test specimens were exposed to vibratory cavitation. Many dislocation rows with various lengths which intersect the specimen surface at 45 degrees were observed uniformly on a(010)or(001)cross section for an as-cleaved specimen. On the other hand, the dense dislocation rows were localized at the roots of surface irregularity for rough specimens. The depht of surface roughness increases with exposure time and the acceleration is hogher for rougher specimens. It is concluded that the dense dislocation rows intiated at the roots of irregular surface is responsible for the growth of the spongelike eroded surface.

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In this study, densification process of the capusle free sinter-Hipping was investigated by using Al₂O₃ experimentally. In green compact with many pores, it is known that the densification of capsule free sinter-Hipping is inhibited when these pores in the inside has been connected with the surface and pressurization gas invades into the pores. Then, for the samples which carried out pressureless pre-sintering using electric furnace at 1100°C, the densification process was traced by measuring the density of the samples at any times of capsule free sinter-Hipping process which was pressurized after the onset of heating. As the results, though the increase of relative density to about 58% was very slightly, the rate of densification was rapidly improved to the end of heating up after it and was lowered during the temperature holding process.

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