Computer simulations are about to replace experiments in various fields. Regarding with this, the scale of model to be solved tends to be extremely large. In order to perform such large scale analyses, the authors propose the parallel use of several computers connected to a network. In other words, a computer network is regarded as a parallel computer. As a parallel numerical algorithm for the fimite element analysis, the present authors have proposed a domain decomposition method combined with an iterative solver, where a whole analysis domain is ficitiously divided into a number of subdomains without overlapping. The present algorithm is first implemented on a network composed of several engineering workstations, and the efficiency is confimed on the EWS network. The system is then successfully applied to the analysis of a sample problem of the order of one million degrees of freedom by using a supercomputer network which consists of several supercomputers.

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With increasing diversity of products, it becomes more and more important to make appropriate decisions at the earlier stages of design. These decisions are more often qualitative. To effectively cope with this situation, we have developed a two dimensional shape model Coded Boundary Representation method. This method represents a shape in the form of a list using directional codes. Its major features are : (1) It can easily process rough sketches, (2) It can extract form features with ease and (3) It is compatlble with the mechanics model. Although most of the conventional models can treat only closed figures, our model can treat open ones as well. What differentiates our model from the newly emerging nonmanifold model is that our model can take into consideration the relation between a shape and loadings. Thus, our model provides a very flexible tool at the preliminary design stage for predicting the mechanical behavior of a product.

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An a posteriori error estimation method for finite element solutions for 3-dimensional elastic problems and plate bending problems is presented. The method is successfully applied to 3-dimensional elastic problems and plate bending problems. In order to decrease the computing time and memory use, error is estimated element by element. The major difficulty in the elemestwise error estimation technique is satisfying the self-equilibrium condition of applied forces in 3-dimensional problems and plate bending problems. These forces are mainly due to traction discontinuity on the element boundaries. The difficulty is circumvented by employing an elementwise optimal procedure. It is also shown that a very accurate stress solution can be obtained by adding estimated error to the original finite element solution.

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A procedure to handle the constitutive properties of materials with crystalline structure in computer simulation is examined, so as to treat mechanical interaction between the macroscopic field and the evolution of microstructures which constitute the elemental mechanism of plastic deformation. In this report, numerical analysis of opening of a central crack in a plane strain block is performed by means of a physical model of plasticity, whose properties are described on the basis of the crystal slip theory proposed by Asaro, et al. and it is shown that this model gives plenty of valuable information in microscale field and it has right to take the place of the phenomenologically formulated constitutive equation in computational plasticity.

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Focusing on thermal distribution during deformation, ductile-brittle transition of α-iron single crystals under constant tensile stresses has been simulated by a molecular dynamics approach where the Newton equations of motion are solved utilizing the Johnson potential. A simulation where the ad-hoc velocity scaling method was used to control the deforming crystal at a low temperature showed brittle fracture starting at the notch in a plane perpendicular to the tensile direction. Another simulation where no scaling was used, where the temperature of the crystal was substantially increased during the deformation, showed plastic deformation at slip planes. From these two types of simulations, brittle-to-ductile transition of α-iron can be attributed to the temperature effect under deformation. Using a definition for local temperature at a nonequilibrium state, a substantial temperature increase was observed to occur near the crack.

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In the analysis of small structure such as the electronic devices, all of the material properties or dimensions of each component can not be grasped clearly in practice. In this study, uncertain thermal deformation of IC package mounted on the printed circuit board is evaluated by the stochastic finite element analysis based on the first order perturbation technique. In the analysis, the uncertainties of elastic constants, coefficients of thermal expansion and the position error of Si chip are taken into account. The numerical example shows the effect of each uncertain factor on the deformation of package lead related to the thermal fatigue of solder joints. Furthermore, the strain of solder joint is estimated by considering the uncertainty of lead deformation.

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A numerical simulation system is developed to estimate the mechanical behavior of a ceramic granule compact in cold isostatic pressing. In this system, a new yield criterion and constitutive equations proposed in the first report are used. Simulated results are compared with results of actually pressed <Al>₂O₃ compact. The agreement between calculated and the measured deformation of compact is relatively good.

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In this paper, an approximate solution for the elastic contact problem between two-layered bodies is proposed. This solution is analytically derived by applying the Hertzian contact theory and assuming stress field in the two-layered body. As a numerical example, the elastic contact problem between a rigid cylinder and a two-layered elastic body, which is composed of elastic film and a semi-infinite elastic body, is treated. From the result, the effectiveness of the present solution is examined by comparison with the Hertzian contact theory and the theoretical solution of Gupta et al.

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In this paper, two approximate solutions to axially symmetric contact problems between two-layered elastic bodies are proposed. These solutions are derived by applying the Hertzian contact theory and assuming stress field in the two-layered body. The difference in the two solutions is dependent upon displacement formulation on the boundary face between different materials in the two-layered body. As a numerical example, the elastic contact problem between a rigid sphere and a two-layered elastic body, which is composed of elastic film and a semi-infinite elastic body, is treated. From the result, the effectiveness of the present solutions is examined by comparing them with the Hertzian theory and the finite-element solution.

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It is important to study the fundamental deformation behaviour, especially the nonuniform distribution of stress and strain in the rubber composite material. In the present paper, tensile deformation of the rubber composite material under the condition of plane strain is analysed numerically with the Mooney-Rivlin-type strain energy function. Namely, a plane model of in-homogeneous material is adopted as a model of a rubber composite material. Ellipsoidal inclusions with different elastic constant are assumed to be placed regularly in the matrix. The problem of the incompressibility of rubber is treated using the penalty function in the finite-element formulation. The incremental load method and Newton-Raphson's method are used for the numerical calculation of the nonlinear problem. It is found that the deformation of the model comes to have a similar mode with that of constant strain as the shape of the inhomogeneous region becomes slender in the stress direction. The distribution of stress and strain in the inclusion is nearly constant.

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In this paper, a finite-element method (FEM) analysis system of nonsteady thermal stress has been developed to analyze the problem of metal-FRP bonded joints. At first an algorithm for analyzing the thermal stress by taking account of the temperature-dependent mechanical properties of adhesion is presented. Then, the effectiveness of the method, that is, the accuracy and central processing unit (CPU) time, has been discussed by analyzing some typical problems. Finally, the thermal fatigue strength of an Al-CFRP bonded joint has been studied through a series of thermal cyclic fatigue tests. It has been shown that the thermal fatigue strength of the joints can be well explained by the maximum equivalent thermal stress at the adhesive layer, which can be analyzed by the developed FEM system.

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Tension tests were carried out for <Si₃>N₄/SUS304 joints at room and high temperatures. Analyses were also conducted for the same specimens using FEM to evaluate residual stresses and stress concentrations. The summaries of the results are shown in the following. (1) The maximum tensile residual stress is σ_z and exists at the same point very near the surface and joining interface, for every Cu thickness and temperature. (2) The maximum tensile stresses occurred in the ceramics/metal joints stressed in tension at room temperatures are constant independent of the middle interlayer thicknesses. The joint strengths are determined by residual stresses and stress concentrations. (3) The maximum tensile stresses in the ceramics/metal joints stressed in tension at high temperatures decrease with increasing temperatures. Therefore, the joint strengths are determined by residual stresses, stress concentrations and decrease of strength accompanied by increase of temperatures.

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A general formulation for the reliability model of unidirectionally fiber reinforced composite laminates is presented, where strength, modulus, load, lamination and dimensional parameters are random variables. In this paper, a method of evaluating the safety index or reliability of unidirectional laminates whose limit state functions are based on quadratic polynomial failure criteria for materials design is proposed. Some standardizing transformation procedures are formulated in order to transform random vectors with correlation into normalized random vectors without correlation. This transformation procedure enables one to evaluate the effectiveness of correlation among probabilistic characters of strength, modulus, load, lamination and dimensional parameters of unidirectional laminate. Some numerical analyses for quantitative effectiveness analysis of correlation coefficients among random variables are presented for graphite/epoxy unidirectional laminate.

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In this paper, thermal stress analyses of all over the integrated circuit (IC), which is molded by resin and subjected to thermal load, are performed in detail. Two models of basic and practical constructions simulating the IC are analyzed. The analytical method is the special finite-element method proposed previously by the authors. In the analyses of basic constitutional models, the influence of the package thickness and the chip size to stress distributions of the IC are evaluated. Moreover, in the analysis of the practical IC model, the causes of failure of an actual IC are also discussed.

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A simulation program which can calculate SiO₂ growth and stress generation caused by growth in the thermal oxidation process of silicon is developed. This process is used in fabricating semiconductor devices. The oxidation process is modeled as a sequence of three primary processes as follows : diffusion of oxidizing species through an already existing SiO₂ layer, Si/SiO₂ boundary movement and dilatation of the transition region from silicon to SiO₂. The finite-element method is used in diffusion analysis and stress analysis, and the body-fit method is used as an automatic mesh generator. In addition, stress dependency and the effect of 'white ribbon' on oxidation are modeled in the program to increase accuracy. Simulation results showed good agreement with experiments of some LOCOS structures with various thicknesses of the <Si_>3N₄ mask.

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This paper presents a new method for the stress intensity factor analysis of two-dimensional problems including a mixed mode interface crack between dissimilar materials. The virtual crack extension method, which is usually utilized together with the finite element method, is an excellent method for evaluating the stress intensity factors. In the present paper, the virtual crack extension method is combined with the boundary element method. A stress analysis is carried out by the boundary element method, and then the virtual finite elements are assumed around the crack tip. The nodal displacements of these virtual finite elements are evaluated as internal points. At first, we applied the present method to a center-cracked plate under tension. Furthermore, we analyzed a plate with a center interface crack and a plate with a center slant interface crack between dissimilar materials subjected to tension. It is found from these analyses that the present method gives very accurate results and that the accuracy of the solution is insensitive to the size of the virtual finite elements around the crack tip.

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To overcome various difficulties in finite element modelling of fast curving crack propagation, an automatic element-control method is developed for moving finite-element simulation. The Present automatic element-control method is based on Lagrangean-element mapping together with a concept of fictitious element-controlling plane. A component separation method of the path independent dynamic J integral is also presented, for the evaluation of mixed-mode dynamic stress intensity factors. Generation phase simulation for a fast curving fracture test is carried out using the present techniques. In the finite element simulation, the formation process of caustic pattern is also simulated for dynamically curving cracks. Shapes of the simulated caustic patterns agree well with the caustic patterns in high-speed photographs, and with those based on a higher-order theory of caustics.

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The present authors proposed the electric potential computed tomography (CT) method for estimating location, shape and size of two- and three-dimensional cracks in conductive bodies from electric potential distribution, based on boundary-element inversion analysis schemes. In the present study, a simplified inverse analysis scheme is proposed to identify surface cracks on back faces by processing the electric potential distribution using a workstation. In this scheme, a hierarchical method is introduced, in which two-dimensional scanning analysis is combined with three-dimensional inverse analysis. To achieve a high-speed computation on the workstation, an analytical expression of electric potential distribution reported by Johnson is used in the two-dimensional scanning analysis, and a data base of electric potential distribution on a three-dimensional cracked body is utilized in the three-dimensional inverse analysis. Numerical simulations and experiments have shown that the proposed scheme is useful for identifying the surface cracks.

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In-plane bending of curved tubes is analyzed numerically in the elastic-plastic range on the assumption of pure bending, uniform deformation along its longitudinal axis and the Kirchhoff-Love hypothesis. The equilibrium equations of pure bending of tubes, derived by E.L. Axelrad, are transformed into incremental forms and solved by the updated Lagrange method. The material of tubes is assumed to obey a power-hardening law and the Prandtl-Reuss flow theory. The curved tube is discretized by a rigid body-spring model, which is composed of rigid plate elements connected with nonlinear springs that are distributed over the ends. The in-plane stiffness and flexural rigidity of the tube wall are obtained by numerically integrating generalized incremental stiffness over the wall thickness. Numerical analyses have been carried out for various combinations of initial in-plane curvature, diameter and thickness of the curved tube. The present analyses simulate well the relation between bending moment and change in curvature, and flattening of cross sections which are obtained by bending experiments in aluminum tubes by Murota and Endo.

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A sensitivity analysis code for the elastic-plastic dynamic response of piping systems is developed in the context of implicit time integration schemes. The formulation of sensitivity analysis originates in the perturbation method and retain its advantage. Namely, the decomposed effective stiffness matrix after the iteration for each increment is efficiently used to compute the sensitivity of any parameter involved in the piping system. A residual heat remover of PWR under an earthquake loading is analyzed based on the present method with the isoparametric elbow element proposed by Bathe, and satisfactory results are obtained.

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The particle flow model is proposed as an improved finite element method for the analysis of metal forging processes. The forged material in the present modeling is analyzed in conjunction with non-material domain, and the process is expressed not by the finite element deformation but by "the movable particle" which discriminates the material domain. The finite element only has a role to give the node velocities which prescribe to the particle where to move. This "fixed" mesh algorithm will free program developers from complicated folding treatment and will free users from irksome task of remeshing as well. This paper describes the outline of the concept and some application examples of two dimensional axisymmetric problem.

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A method is proposed to find the shapes of soft bodies based on discretized modeling of the body surface. The surface of the body is discretized in forms of conical segments or triangular segments, whose nodal coordinates are taken as unknowns. The condition that the volume of the body is constant is employed as an equality constraint condition and incorporated in terms of the Lagrangian multiplier in the functional to represent the minimization of surface free energy and gravity energy. The linearized governing equation of the unknowns is derived from the stationary condition of the functional. The numerical examples of the shapes of foam and spheroid verify the validity of the proposed method.

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Bifurcation buckling will occur under internal pressure in the top end closure of cylindrical oil storage tanks with fixed roofs. In the design of the tanks, the shell-to-roof joint is considered frangible and is expected to fail before failure occurs in the shell-to-bottom joint. This paper describes the buckling analysis of the top end closure of the tank. The influence of both the tank diameter and the slope angle of the roof on the buckling internal pressure is investigated by the axisymmetric finite-element method. Large-deflection elastic analysis in the prebuckling state is performed. The values of the buckling pressure obtained by FEM are compared with those calculated by a formula of API standard 650, which is a design code for the oil storage tanks. Results show that the API formula gives smaller buckling internal pressure than FEM in the range of the small tank diameter, and seems to underestimate the pressure from the viewpoint of the frangible joint.

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A torispherical shell is known to buckle with circumferential waves on a knuckle region when it is subjected to excessive internal pressure. The circumferential waves observed are caused by bifurcation buckling. A torispherical shell is utilized as a head of a Boiling Water Reactor (BWR) contaiment vessel or a Fast Breeder Reactor (FBR) vessel or a component of chemical Plants. It may buckle due to overpressure caused by accidents. Dynamic loading may act on a torispherical shell due to accident. In general, the bifurcation load is lower in the case of dynamic loading than in the case of static loading. Therefore, it is important to obtain the bifurcation load for a torispherical shell due to dynamic loading from the viewpoint of estimating the safety margin of a torispherical shell under accident conditions. In the present paper, we calculate the bifurcation buckling pressure for the torispherical head of a Mark II-type BWR containment vessel, using a finite element program for a dynamic analysis. Three kinds of loading, that is, static loading, step loading and impulsive loading, are considered in the present analysis. The minimum bifurcation buckling pressure is predicted for the respective loadings.

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The numerical methods which have been proposed by the present authors for investigating the characteristics of waves in a functionally gradient material (FGM) plate and its transient responses are expanded for functionally gradient piezoelectric material (FGPM) plates. The material properties of the plate change gradually in the thickness direction, and are anisotropic in the plane of the plate. The plate is divided into N plate elements. The variational principle is used to derive approximate governing equations. The dispersion relation and the mode shape of the waves are obtained by using mechanical ane electrical boundary conditions. The energy velocities of the waves are formulated with the aid of the Rayleigh quotient. The method of Fourier transforms in conjunction with modal analysis is used to determine the displacement and electrostatic potential responses excited by mechanical loads and/or interdigital electrodes. The formulation of the theory is described in this paper.

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The numerical methods presented in the previous paper for the wave propagation analysis of anisotropic functionally gradient piezoelectric material (FGPM) plates are applied to a hypothetical FGPM plate. The frequency spectum, energy velocities, electromechanical coupling constants, and the mode shapes of the waves in the FGPM plate are obtained. The transient responses of the FGPM plate excited by a line time-step impact load, a line electrode, and interdigital electrodes are computed. The results obtained for the FGPM plate and a homogenous z-x LiTaO₃ plate are compared. It is found that the displacements are much more concentrated on the softer surface of the FGPM plate than on the surfaces of the homogeneous plate, and that the displacement responses corresponding to the surface waves of the FGPM plate are larger than those of the homogeneous plate. A pseudo-SH surface wave whose penetration depth is as small as that of the Rayleigh wave is discovered.

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Various element mass matrices are considered for the bar and beam elements. To clarify the characteristics and accuracy of the mass matrix of bar and beam elements for vibration analysis, assembly of two neighboring elements produces the finite difference equation for the i-th node. From finite difference arguments it is shown that the state of convergence of the frequency. The optimal element mass matrix is presented for bar element.

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This paper is concerned with the optimal adaptive geometries of intelligent truss structures under dynamical loadings. The optimal geometry is attained by changing the lengths of some active members installed in the structure to obtain the maximum structural strength. Dynamical analysis by Newmark β method is introduced into the geometry optimization problem. The intelligent truss structure is assumed to be either fixed at the base or in a floating state. From the numerical examples, the following conclusions are drawn : (1) For an impact load, the largest stress exists in the place which is directly subjected to the impact and the geometry of the structure cannot improve the structural strength, (2) For a load acting for a long time, there exists an optimal geometry which provides a much higher structural strength than other geometries of the structure.

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In design environment, most of variables and parameters such as loads, strength, sizes and material constants have some randomness and/or in many cases designers can't know exact values of those variables. In such a case, the concept of reliability shoud be included in the design object instead of conventional safety factor. This paper proposes a problem of optimum shape design for 2 dimensional continuum, taking the reliability concept into consideration. When sizes, strengths and outer forces vary according to the normal distribution, such a shape is determined that minimizes the average volume under the constraint of failure probability. In the body with the obtained shape, the probability of failure is uniform.

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A trial development of a system for the deformation analysis of beams is performed using an object-oriented approach. The basic consideration for designing necessary classes and their hierarchical structure for the deformation analysis of beams is presented. The concepts for design massages and methods am described. Methods for dealing with synonymic masseges and for dealing with physical dimensions such as those of force, moment, and length are proposed. The easiness of the extension of the knowledgebase is illustrated by adding the knowledge on the analysis of continuous beams and the analysis of nonliner deformation problems. The object-oriented paradigm is shown to be useful in the field of structural engineering.

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Computational mechanics are based on numerical methods and high-performance computers while artificial intelligence (AI) tools are based on knowledgebases. A new concept on structural analysis by using AI technique is presented in this paper. A fully artificial intelligence approach has some significant meanings: 1) The field of computational mechanics should include problems which shows very complicated phenomenal behavior, but have low degree of freedom. 2) An approach supporting the conceptual design stage of structures should provide a very flexible simulation capability of structural behavior. Artificial intelligence tools will provide some solutions to these. The purpose of this research is to investigate the benefits derived from the application of an artificial intelligence approach to structural analysis fields. A prototype knowledge-based system, called OOTA (Object-Oriented Truss Analysis), is developed to analyze me truss structures. Since the system does not use any numerical method, the computation requires much time. But, it provides many advantages for small but complex problems including material and geometric nonlinearlities.

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In this paper, the structural reliability theory is applied to multiaxial fiber-reinforced laminate systems. The first-ply-failure criterion is adopted for the reliability analysis of the laminate systems, and the multiple-check-point method is successfully applied to evaluate the reliabilities of biaxial, triaxial and tetraaxial laminates under the probabilistic in-plane stresses. The reliability-based optimum fiber orientation angles of multiaxial laminates are determined and compared with those under the deterministic conditions. Further, some effects of the random properties of loads and strengths are discussed. From the numerical results it is concluded that the optimum fiber orientation angles of laminates are very different between the deterministic and probabilistic conditions and that the reliability of the multiaxial laminates increases with the increase in the number of orientation axes under probabilistic conditions. As a result, the optimum laminates approach quasi-isotropic construction when the uncertainty in the stresses and strengths is taken into consideration.

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A personal computer program using the intelligent Finite-Element Method (FEM.) has been developed in order to analyze the components and its stacking sequence of laminate by which some design objects are satisfied. In this paper, the strength and the weight of laminate have been selected as the design objects. Taking these design objects into consideration, as the examples, a laminated plate under the conditions of bending and combined loads of bending and tension have been analyzed, and optimum laminated materials and stacking sequence for each condition have been determined. Therefore, it is recognized that the proposed intelligent FEM. in this paper is very useful for structure design of composite materials.

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The inverse problem under consideration deals with the identification of unknown defects in structural components by using the elastodynamic boundary element method and the optimization technique. In the inverse problem, identification results are greatly influenced by the errors included in additional information. This study is concerned with a numerical experiment to investigate the influence of measurement errors in the given additional information on the identification results. Numerical simulation is carried out for two-dimensional example problems when the displacement responses given as additional information include probabilistic errors with the normal distribution. In addition, a practical method is proposed for improvement of accuracy in identification.

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The boundary integral equations conventionally used for thin elastic plate bending analysis have the singularities of the Cauchy principal value order for which special care must be taken in numerical evaluation when the boundary is discretized by using the higher-order elements. In the present paper, the boundary integral equations are regularized up to an integrable order by using the subtracting and adding back technique. The obtained boundary integral equations both for deflection and rotation are weakly singular, and their discretized forms can be integrated accurately by the standard Gaussian quadrature formula. Numerical implementation of the resulting regularized integral equations is presented, and effectiveness of the proposed method is discussed through some numerical demonstrations.

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Accurate computation of boundary stress components is impotant in some engineering problems such as structural shape optimization. In the present paper, we propose a new approach to calculate the boudary stress components using the boundary integral equation which relates the boundary displacement gradients to the boundary tractions. Although the original integral equation must be evaluated in the sense of the Cauchy principle value, it can be regularized by subtracting and adding back the displacement gradients at the source point and can be evaluated numerically using the standard Gaussian quadrature. Numerical implementation of the proposed integral equation is presented and the effectiveness of the approach is also discussed through some numerical demonstrations.

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A stiffness approach is at first generally described for mechanism motion analysis. The kinematic system is regarded as an instable elastic structure and the tangent stiffness equations are updated for the current mechanism configuration. The obtained singular stiffness matrix is then used to predict incremental rigid-body motions. The nonlinear incremental mechanism equations are established and its solution procedure is proposed to follow successively the mechanism motion in an incremental/iterative manner. Secondly, the tangent stiffness matrix is obtained by formulating the slider mechanism motion as a contact problem. The proposed nonlinear scheme and the obtained stiffness matrix for the slider mechanism prove to work well in computed numerical examples. The stiffness approach in the present study may be incorporated into existing finite-element program systems and can be applied to general three-dimensional mechanisms.

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Recently, in order to improve power plant thermal efficiency, the turbine blade, which is the most important element of the turbine, has been used in the severe condition. Especially the blade root, which is inserted into a disc groove, supports the excessive centrifugal force. In this paper, effective methods of calculating the peak stress of the blade root and disc groove are presented. Since the geometry of the blade root and disc groove is complicated, the three-dimensional finite-element method is applied, including the nonlinear effect due to slippage between the root and groove. By using the above nonlinear finite-element method, contact and slip analysis is performed to obtain the converged peak stress. The effective linear analysis procedure for replacing the nonlinear analysis is also examined by comparing the calculated results of both methods.

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A computer image processing system incorporated into specially designed servo-hydraulic fatigue loading facilities operating in a scanning electron microscope has been developed. Direct, real-time observations of fatigue crack growth behavior under both constant amplitude and repeated two-step loadings were made, and quantitative analysis of crack opening displacement and deformation near the fatigue crack tip were made using a newly developed image processing technique.

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A method for applying a. c. potential drop technique is proposed to evaluate the stress intensity factor K_I for a 3-D surface crack. The effect of load on a. c. potential drop measured on the surface of a specimen which contains a 3-D surface crack has been utilized to evaluate K_I for the crack. The analysis of the inverse problem has been done for determining K_I, where the measurements of the change in potential drop due to the change in load applied to the specimen have been compared with theoretical computations which include K_I as an unknown quantity. The measurements have been done under three-point bending for a semielliptical surface crack introduced by fatigue. The evaluated value of K_I based on the present method has been compared with the solutions of elastic analyses reported so far, and the present method has been verified.

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In this paper, the dependence of fracture toughness on the crack length is examined, at room temperature. The specimen used is HP sintered <Al>₂O₃. The statistical properties of fracture stress of plain specimen σ_F and fracture toughness K_C are examined under the same experimental conditions. Also, a failure assessment diagram is proposed based on both the process zone size failure criterion and probabilistic concept. Lastly, the relation between process zone size and grain diameter is discussed.

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Brittle fracture surfaces at room temperature (∼25°C) and -196°C for molybdenum single crystal were observed with scanning tunneling microscopy (STM) and scanning electron microscopy (SEM). STM images obtained showed that the fine cleavage steps were formed on the fracture surfaces. The images were analyzed by fractal geometry. Brittle fracture surface of molybdenum single crystal had self-similarity (i.e., fractal character) up to very high magnification where the scanning range of 40 nm in X and Y directions corresponded to about 150 atoms of molybdenum. However, this charactor was expected to break down when the scanning range in X and Y directions were below 20 nm. This is confirmed by STM image with the scanning range of 16 nm, where the cleavage step was not observed.

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When nickel foil strain gages are stuck on the surface of a specimen subjected to repeated loads, the elastic stress is measured by observing slip bands in the foil gages resulting from repeated strains. Calibration studies with rotating-bending tests at temperatures from 100°C to 350°C are performed on round steel bars with nickel foil, and the threshold stresses for the first appearance of slip bands are examined at variable temperatures rising directly. Furthermore, assuming that the first appearance of slip bands is subject to the linear cumulative damage law, the threshold stresses at the variable temperatures are calculated from those obtained by the calibration tests at several definite temperatures. The peak stresses in grooved shafts subjected to bending at the variable temperatures are measured with the nickel foil gages. The results are compared with those obtained previously by various methods.

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Governing-equation inverse problems deal with an inference of a differential equation governing a field quantity from observations. In the present paper an inversion scheme was proposed which reduced the identification of the governing differential equation to the estimation of the order and the coefficients of the differential equation. The values of the field quantity observed under several conditions were simultaneously used in the estimation. Numerical simulations were made on the applications of the proposed scheme to the identification of a second-order ordinary differential equation and a second-order partial differential equation. It was found that the proposed scheme was useful for estimating the governing differential equation, even when the order of the differential equation was not known in advance.

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This paper is concerned with material-property inverse problems, in which material properties of individual components of a discrete system are estimated using the response of the system to several sets of external input. Two inversion schemes were proposed for estimating the material properties : the [K] matrix method and {C} vector method. The [K] matrix method determined a stiffness matrix of the system for estimating material properties. The {C} vector method was based on the stiffness equations expressed in terms of the {C} vector whose components consist of parameters of material properties. Formulations were presented for estimating conductance and stiffness of components of trusslike structures. Constraints based on information on material properties can be introduced in the {C} vector method. Numerical simulations were made of the applications of the methods to the estimation of conductance of trusslike structures. It was shown that the proposed methods were applicable to the estimation of material properties of discrete systems. The proposed methods can be applied to continuous systems with minor modifications, when discretized equations using numerical schemes, such as the finite-element method and the boundary-element method, are used in the formulation.

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Environmental degradation due to temperature and humidity has been studied by infrared (IR) spectroscopy on polyethylene (PE), cellulose-acetate (CA) and polycarbonate (PC) films. Specimens were exposed in a vessel at a constant temperature and humidity for 12∼40 days, and tensile tests of the specimens were carried out at room temperature. The weight, the water absorption and the IR-absorption spectra of the specimens were also measured before the exposure and after. Due to the effects of environment, the change of the weight and water absorption occurred for CA, but not for PE and PC. For CA the weight decreased for all exposure conditions while the water absroption increased with humidity. The variation of fracture strain and yield stress was observed for CA, but not for PE and PC. Similarly, only for CA the rate of IR absorption at 745 and 1288 cm^-1 decreased with humidity. Linear relationships were found between mechanical properties and the rate of IR absorption.

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In-situ observation of the materials being damaged by aqueous corrosion and corrosion fatigue with high magnification is significant for the understanding of these mechanisms. In this study, in-situ observation of Au, Fe, SUS304 steel and SNCM439 steel under potential control in 1% NaCl and 0.1% HNO₃ solutions is performed by STM. The STM image can be observed for all materials both in anodic and cathodic potentials if the proper tunnel bias is applied. In cathodic potential the STM image does not change with time, while in anodic potential the STM image changes rapidly unless the material is passive condition.

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