Failure of microelement such as a conductor in an LSI originates mostly from an atomic-scale defect. In this study, the nucleation process of grain boundary groove in an aluminum conductor is analyzed in terms of atomic mechanics. The motion of atoms near an intersection between grain boundary and surface near the melting temperature is simulated by the molecular dynamics. It, however, is impossible to analyze initiation of groove at the intersection in an actual component at its operating temperature by the molecular dynamics because the simulation can only reproduce the behavior of atoms over a very short period (about lO^-9 sec) due to the limitation of computational resources. A Monte Carlo method to simulate the atomic behavior in a longer period is proposed, focusing on the jumps of atoms along the surface. The grooving at a reasonable temperature is successfully simulated by the proposed method.

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Mechanical remodeling of bone is a kind of adaptation and is performed to regulate the stress and/or strain in the tissue in response to the changing mechanical environment due to tissue growth and atrophy. We propose a phenomenological model of mechanical remodeling of bone structure considering residual stress. The lattice continuum model is used to represent the bone structure, such as the trabecular structure of cancellous bones. The basic idea in the previous report, which concerns mechanical remodeling that takes into account the residual stress, is extended to the continuum with the internal tissue structure. A remodeling rate equation of the tissue structure is expressed so as to result in an equistress state at the remodeling equilib-rium as an optimality of the bone structure in the steady state. A case study of a long bone under bending moment reveals basic features of the proposed model of the stress regulation process. Remodeling simulation for the vertebral body under repetitive bending with compression demonstrates apparent density and residual stress distribu-tions that coincide with the experimental observations.

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To simulate not only plastic deformation of a workpiece but also that of a shot in a peening process, the effect of the interaction between the shot and workpiece in the collision is included in the dynamic rigid-plastic finite element method. In the formulation, the equilibrium equations of nodal forces are solved simultaneously with velocity boundary conditions at the interface between the workpiece and shot for sliding and non-sliding contacts. Axi-symmetric plastic deformation in peening of a circular workpiece with a single shot is computed. The calculated shapes of the workpieces and the shots are in good agreement with the experimental ones for plasticine workpieces and shots. It is shown that almost no plastic deformation of the shot occurs under actual shot-peening conditions for steel workpieces when the flow stress ratio of the shot to the workpiece is larger than two.

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Calculations of SiO₂ static-fatigue strength are used to show that the strength-degradation behavior of the material under the influence of the ambient atmosphere can be analyzed using an interatomic potential which is based on the Tersoff potential but extended to take charge transfer effects into account. The force-elongation curves of the Si-O interatomic bonds of the SiO₂ are calculated with and without H₂O in the atmosphere. Based on these curves, crack propagation behavior is analyzed, and calculated results are shown to correspond well with experimental results. Moreover, the calculated values of the strength decrease caused by the H₂O also show fair agreement with the experimental values.

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Molecular dynamics simulation was performed on bcc α-iron having two different lattice orientations which both included a primary slip direction <111> in the plane of applied tensile stress. Cracks on the (100) and on the (011^^-) plane with crack growth-edge direction [011] were studied. For cracks on the (100) plane, no nucleation of dislocations was observed, and the cracks propagated in both low- and high-temperature environments. For those on the (011^^-) plane, brittle fractures without nucleation of dislocations occurred at low-temperature, but at high-temperature nucleation of [111] dislocation from the crack tip was observed. Local stress on the cleavage plane and on the slip plane are discussed from the viewpoint of the fracture mechanism.

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A three-dimensional transversely isotropic constitutive model of cardiac muscle is proposed. Stress in the cardiac muscle is first divided into the sum of passive and active parts. The passive part is represented by a strain energy density function of the exponential type, while the active part is formulated by introducing internal variables describing the activities and the sarcomere length. The evolution equations of the internal variables are established by taking account of excitation-contraction coupling. Comparison of the simulation results with those of experiments in the literature shows that the present model can describe qualitatively the mechanical properties of cardiac muscle.

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It is known that intrinsic mechanical stress exists in a general free surface or interface, because of surface atomic structure changes relative to the bulk. We present an analysis of using the interrelationship between surface stresses, free surface and volume stress deduced in our previous paper. The surface stresses are closely related to the surface energy and surface geometry (mean curvature) of materials. In the present paper, an elastic contact problem in which an axisymmetric elastic body is pressed into an elastic half-region coated with a thin elastic film is analyzed using the three-dimensional theory of elasticity. In this analysis, the relevant dimensionless parameter, called the elastic capillary number, which is a function of surface energy, elastic modulus and the film thickness, is introduced. It is shown that the elastic modulus of the thin film apparently increases and the bulk stress also increases when the surface stresses are taken into account.

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The stress and strain in a very thin film under uniaxial tension are analyzed based on the motion of particles in the film by means of two-dimensional molecular dynamics (MD) simulation. The Lennard-Jones(L-J) potential is assumed as a two-body potential. The tensile load is applied by elongating the fundamental cell longitudinally. The numerical results show that the stress decreases considerably as the size of the region for defining the stress decreases. It is found that more than 130 particles are necessary in the region for the stress concept to be applicable in continuum mechanics.

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In this paper we describe a new user-friendly structural design system for pressure vessels, which is based on finite element stress analyses. The basic concept of the developed system is to minimize input data required for the finite element analysis and to perform the analysis quickly. To realize this, the system is equipped with the finite element modeling module based on fuzzy knowledge processing, the input data generation module, the finite element analyzer, the graphic user-interface module for analysis results, and the stress evaluation module. Fundamental performance of the present system is clearly demonstrated through the analysis of a top nozzle.

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When a transversely isotropic solid cylinder is subjected suddenly to a uniform temperature rise, a stress wave occurs at the surface the moment thermal impact is applied. The stress wave at the surface proceeds radially inward to the center of the cylinder. The wave may accumulate at the center and give rise to very large stress magnitudes, even though the initial thermal stress is relatively small. This phenomenon is called the stress-focusing effect. In this paper we analytically analyze the effects of these waves using the ray series. The results give clear indications of the mechanism of the stress-focusing effect in a transversely isotropic solid cylinder.

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It has been found that the boundary integral equations for steady problems such as those of potential, elasticity, fluid mechanics and so on can be regularized by introducing relative quantities of field functions. This paper describes that fundamental integral equations for unsteady heat conduction problems can also be regularized by applying the same techniques. The regularized integral equations with relative quantity are obtained by superposing a particular solution under the condition of time-independent uniform potential upon the conventional ones. This approach has made it possible to derive the integral equation of potential gradient on a surface point, which has not been given up to now in the conventional formulation due to hyper-singularity. Through two-and three-dimensional numerical investigations, it is verified that the present integral equations give accurate numerical results everywhere over the domain and that they are valid and effective.

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A systematic method of spall damage analysis was developed on the basis of damage mechanics. By use of a scalar damage variable, the damage evolution equation of Lemaitre et al. and the viscoplastic constitutive equation of Perzyna modified for damaged materials were incorporated into the commercial finite difference program MANJUSRI-3D for nonlinear dynamic analysis. The spall damage process, and stress wave propagation and temperature histories were analyzed for plate impact of OFHC copper disc targets. The computational results for the stress history and the particle velocity at the rear surface of the target plates were compared with the corresponding experimental results.

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Structural components operating at high temperatures in power plants are subjected to interaction of thermal fatigue and creep which results in creep-fatigue damage. In evaluating the life of those components, it is important to understand microscopic damage evolution under creep-fatigue conditions. In this study, static creep and creep-fatigue tests with tensile hold-time were conducted on a SUS 304 stainless steel by using a high-temperature fatigue testing machine combined with a scanning electron microscope (SEM), and cavity growth and coalescence behaviors on surface grain boundaries were observed continuously by the SEM. Quantitative analysis of creep cavity growth based on the observations was made for comparison with theoretical growth models. As a result, it was found that cavities nucleate at random and grow preferentially on grain boundaries in a direction almost normal to the stress axis. Under creep condition, the cavities grew monotonously on grain boundaries while remaining an elliptical shape. On the other hand, under creep-fatigue conditions, the cavities grew due to the effect of the local strain distribution around the grain boundary due to cyclic loading and microcracks of one grain-boundary length were formed by coalescence of the cavities. Also, cavity nucleation and growth rates under the creep-fatigue condition were more rapid than those under the static creep condition and the constrained cavity growth model coincided well with the experimental data for creep.

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An incremental theory is developed to describe the elastic-plastic behavior and damage behavior of particulate-reinforced composites, based on Eshelby's (1957) solution for an ellipsoidal inclusion and Mori and Tanaka's (1973) concept of average stress/strain for a finite concentration of particles. In the composites containing hard spherical particles in a ductile matrix, debonding of the particle-matrix interface is a significant damage process, since the accumulation of the debonding damage affects the deformation and strength of the composites. The debonding damage is assumed to be controlled by the stress of the particle and the statistical behavior of the particle matrix interfacial strength. During debonding, the stress of the particle is released and the site of the particle is regarded as a void, resulting in a void concentration which increases with deformation. The theory describes not only the reinforcing effect due to the intact particles but also the weakening effect due to the damaged particles. Analysis of the stress-strain response under uniaxial tension has been carried out on the particulate -reinforced composite based on the present theory. The influence of the damage on the stress-strain relation of the composite is very strong and depends on the statistical properties of the particle-matrix interfacial strength.

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Nonlinear fracture behavior of stepped-lap bonded joints is studied. The joints used have adherends of eight kinds of metals: three of carbon steel, four of aluminum alloy and one of brass. The joints also have various thicknesses, lap lengths and step numbers. The effect of Young's modulus and yield strength of adherend material on the joint strength is calculated by means of elastoplastic finite-element analysis. It is found that the strength of the joint which yields at an adherend corner is nearly equal to the yield strength of the adherend material, because the displacement of the adhesive layer increases abruptly after the adherend yield and exceeds the layer's deformation capacity. The joint strength diagrams obtained by the strength prediction method applying our adhesion criteria show good agreement with the experimental results for all currently available joints having various dimensions and materials.

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We describe numerical analysis methods for multiobjective shape optimization of linear elastic structures. As an example, we consider a multiloading mean compliance minimization problem with a volume constraint. The methods presented here are based on the traction method, in which the speed field representing the domain variation is analyzed. A weighted lp-norm method with four types of norm is employed to scalarize the multiobjective functionals. The shape gradient functions for each scalarized objective functional are obtained using the Lagrange multiplier method. A general-purpose finite element code is used to perform the numerical analyses. Numerical analysis results for a multiply connected plate problem and a solid structure problem under multiloading conditions are presented to demonstrate the validity of the traction method in obtaining Pareto optimal solutions.

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This paper deals with optimization of truss topology using boundary cycle in algebraic topology. Elimination of unnecessary members from the ground structure, one of the popular means to optimize truss topology, is employed. The elimination has a disadvantage that unstable structures possibly appear in the process of the optimization. Boundary operator, which has the ability to represent equilibrium of internal force in members, is used to generate the boundary cycle from chain. Design variables derived by the boundary cycle can always satisfy this equilibrium and avoid a category of unstable structures without imposing any constraint. An attempt is made through numerical examples to minimize the total weight of a plane truss, which is fixed to a rigid wall and supports a vertical load acting at a point distant from the wall, under the condition that the distribution of strain energy density is uniform and equal to a certain value. The validity of this formulation is verified by the numerical examples concerned with the weight minimization of the truss.

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An ultrasound detection system with optical heterodynes shows nonlinear behavior in the large-amplitude region (>λ/8, λ: wavelength of detecting light), and entails some problems in the measurement of laser ultrasound (ultrasound generated by laser deposition), especially for thin specimens. We studied the mechanism of the nonlinear response and found a method for improving it. Through experiments, we devised an improved demodulation method using signal processing techniques to extract actual ultrasonic waveforms in the large-amplitude region, and confirmed its effectiveness. We also carried out numerical experiments to investigate the characteristics of our improved demodulation method and the standard demodulation method. The results show that compared with the standard demodulation method, our method is more robust against noise of beat signals, and more useful for measuring laser ultrasound even in the small-amplitude region.

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The microstructure of newly developed yttrium-oxide-dispersed tungsten alloy was investigated by examining the effect of sintering temperature on the particle size of yttrium oxide and the crystal size of tungsten. Also, it was confirmed that the bending strength of yttrium-oxide-dispersed tungsten alloy was more strongly affected by the sintering temperature in comparison with a sintered tungsten sample. The residual stress, induced by the coefficient of thermal expansion mismatch, is analyzed for the tungsten matrix composite with a particle of yttrium oxide using the finite element method. Because of the high residual stress, particles of yttrium oxide become crack initiation sites under the fabrication process. Finally, it is also shown that the bending strength of yttrium-oxide-dispersed tungsten alloy can be estimated simply by the fracture mechanics approach, based on the assumption of a flaw introduction effect by the yttrium oxide dispersion.

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Crack propagation tests were carried out in various environments from water to vacuum using compact tension specimens. The main results obtained are as follows :(1) In vacuum, the crack propagation rate under cyclic load is faster than that under static load. Cyclic fatigue can occur without the presence of water vapor. This behavior is substantial cyclic fatigue in this material. (2) The degree of crack propagation rate acceleration increased as partial pressure of water vapor rose. (3)These results are explained by the mechanism in which the origin of the cyclic effect is the decrease in the stress shielding effect by cyclic load. In this respect, the only necessary condition for cyclic fatigue is not stress corrosion cracking due to water vapor but load cycling.

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Oxidation kinetics of as received and preheat-treated C/C composites fabricated by the preformed yarn method were investigated. The weight loss due to gasification was measured with oxidation time. In situ observation of microscopic morphological change due to oxidation was conducted using a laser microscope during heating in flowing air. Then, degraded inner and outer morphologies of C/C composites oxidized at various temperatures were examined through observation by SEM and measurement of pore distribution using a mercury porosimeter. As a result, degraded morphologies due to oxidation were extremely different depending on the oxidation temperature range. The inner structural changes became obvious as the oxidation temperature decreased. Therefore, the rate-determining process of the oxidation was changed from the surface chemical reaction to reactive gas diffusion across the boundary layer of a gaseous oxidation product as the oxidation temperature increased. The oxidation reactivity of C/C composites was related to metallic impurities such as iron and residual stress generated during fabrication.

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In order to investigate crack growth characteristics due to thermal striping in liquid sodium coolant used for fast breeder reactors (FBRs), thermal striping tests in sodium have been conducted using Type 304 stainless steel and material produced by plasma carburizing Type 3o4 stainless steel. The results showed that the threshold stress intensity factor range, derived from a thermal stress analysis under the condi-tion of plane stress, could be used to predict the final lengths of the nonpropagating cracks. The depths of nonpropagating cracks increased with increasing carbon content. This tendency was attributed to the difference of the stress intensity factor range, caused by the difference in Young's moduli of the materials.

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Atomic force microscopes (AFMs) can be used for atomic-scale imaging and nanofabrication. Taking advantage of this we developed a nanoindentation technique. Hardness measurements were carried out on cementite-spheroidized S 25 C carbon steel (Vickers hardness H_v =128) and 400°C-tempered SNCM 439 low alloy steel (H_v =414), using a cantilever with a three-sided pyramidal diamond tip. The depth of indentations created was between 14 and 330 nm. The difference in hardness between S 25 C and SNCM 439 steels was detected in the nanoscopic region. From these results, it was concluded that nanoindentation was realized with AFM

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