In order to clarify the characteristic feature in the deformation behavior of particulate-reinforced composite materials, a homogenization method has been developed for the materials obeying the strain and strain-rate dependent constitutive equation that takes into account for the characteristic length scale by using the strain gradient theory and developed the corresponding finite element method. By means of the computational simulation under the plane-strain condition, a series of simulations with inhomogeneous deformation behavior of composite materials containing different volume fractions, size and distribution pattern of reinforcement subjected to different loading direction have been performed. As a result, it has been clarified that the resistance of composite material to deformation is substantially increased with the refinement of the particle size and significantly dependent on the loading direction under constant volume fraction of the reinforcement. This result indicates that the present simulation method has the capability of predicting the experimentally observed particle-size-dependent macroscopic characteristic feature of the composites. The main mechanism of the increase of the deformation resistance in the plastic range is attributable to the high strain gradient appearing in the matrix material, which increases with decreasing the distance between the particles. Therefore, the regularization of the distribution pattern that increases the value of the maximum strain gradient in the matrix contributes toward improving the resistance to macroscopic deformation behavior.

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In this work, we describe the implementation of a parallel iterative solver in a large structural analysis program. To achieve maximum performance and stability for the solver, we needed to develop a parallel preconditioner. The preconditioner we use is Factorized Sparse Approximate Inverse. This preconditioner requires only the same amount of storage as the stiffness matrix and has excellent scalability. We devoloped a parallel structural analysis system using this iterative solver and look at a large industrial problem. The numerical results show the effectiveness of this solver.

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The transient thermoelastic behavior of the functionally graded plate due to a thermal shock with temperature dependent properties is studied in this paper. The development of a micromechanical model for the functionally graded materials is presented and its application to thermoelastic analysis is discussed for the case of the W-Cu functionally graded material for the International Thermonuclear Experimental Reactor divertor plate. The divertor plate is made of a graded layer bonded between a homogeneous substrate and a homogeneous coating, and it is subjected to a cycle of heating and cooling on the coating surface of the material. The thermal and elastic properties of the material are dependent on the temperature and the position. Numerical results presented, include the transient temperature distribution and the transient thermal stresses.

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The tensile test of three type of SiC particle reinforced 2024-T6 Aluminum alloy are conducted by changing the reinforcement volume as 0%, 2% and 10%. The stress-triaxiality of the specimens are changed 0.33, 0.56, 0.75, 1.0, 1.46, 1.94 and 2.5 by changing the notch radius of the specimens. The effect of stress-triaxiality on void configuration is investigated under the SEM (Scanning Electron Microscope) and 3-dimensional imaging analysis. The experimental results show that the void diameter and depth changed with the change of SiC particle volume fraction and stress triaxiality in the base matrix. The number of small void increases and the number of large voids decreases with the decrease of the stress triaxiality and SiC particle volume fraction. The number of small voids decreases and the number of large voids increases with the increase of the stress triaxiality and SiC particle volume fraction. The aspect ratio of the voids increases with the increase of the void diameters.

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The purpose of this research is to estimate fiber length in a 3-dimentional short fiber reinforced composite without extracting the fibers. The author leads the relationship between the fiber length and the number of visible parts observed under the composite surface based on the probabilistic method. The visible part is the section that the fiber observed under the surface is interposed between other fibers and so on. The number of the visible parts interposed between the embedded fiber tip and another fiber and the number of those derived from embedded fibers are evaluated separately. As for the number of the all visible parts, it is found out that the influence of the fiber length is not taken very much as the result of the numerical calculation. On the other hand, as for the number of visible parts interposed between the embedded fiber tip and another fiber and the number of those derived from the embedded fibers, it becomes clear that they are sensitive to the fiber length. It is pointed out that it is possible that the fiber length is estimated by using those numbers.

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Alumina-fiber-reinforced epoxy (alumina/epoxy) is often used in making the thermal insulating structure of superconducting magnet because it is stiff and strong and has a low thermal conductivity. The stiffness of the alumina/epoxy structure is one of the factors determining the soundness of a superconducting magnet, so it is important that the relation between the degradation in stiffness and the growth in the size of defects in alumina/epoxy is determined. A new defect-monitoring method using light transmitted through alumina/epoxy has therefore been developed. Defects inside a semitransparent alumina/epoxy laminate will scatter the light and decrease its intensity. The spectra of the transmitted and reflected light were measured using a spectrometer in order to identify the wavelengths most sensitive to defects in alumina/epoxy. With decreasing stiffness, the intensity of transmitted light decreased and that of the reflected light increased. These changes were most obvious at wavelengths from 400 to 800 nm, so it seems that measuring the intensity of transmitted visible light is a promising method for assessing the structural integrity of alumina-reinforced epoxy.

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This paper describes the reliability analysis of a simply-supported laminated composite plate with an initial imperfection under a bi-axial compression load. For a plate loaded in compression, a small initial imperfection can cause large bending stress that decreases a plate failure load. The first ply failure criterion is adopted as that of the plate failure. On the reliability analysis, the laminated composite plate is modeled as a series system consisting of the composed plies, which means that failure in any one ply reduces to failure of the plate. The initial imperfection, material properties and applied loads are considered as random variables. The mode reliability is evaluated by the first order reliability method (FORM). The system reliability is approximated by Ditlevsen's upper bound. Through numerical calculations, the effect of variations of the random variables is evaluated on the reliability. The change of the reliability in terms of ply orientation angles is also investigated. The reliability-based optimum design is demonstrated to be different from the design of deterministic strength maximization. The results show the importance of considering variations of the random variables for the safety of a laminated composite plate.

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There is interaction among multiple cracks which are initiated in a plane surface by fatigue or environmentally assisted cracking. And it is observed that these cracks may coalesce as they approach each other. In this study, the interaction of multiple cracks with different relative locations and lengths was evaluated using a finite element method. Furthermore a program which would generate a finite element mesh depending on their different locations and lengths was developed. This program then was used to simulate the growth of two cracks as their distance is getting smaller, with their unsteady interaction taken into consideration. The simulation provided new knowledge about two cracks whose growth reduces their distance ; when two cracks are not brought into coalescence, the interaction due to their greater contiguity makes the outer crack tips of the two cracks grow faster than a single crack. And the time to fracture involving two contiguous cracks becomes almost the same as the time required for coalesced cracks to lead to fracture. Finally, Monte Carlo simulations were performed to reproduce the crack initiation and growth on a computer. The simulation gave a realistic distribution form which shows that multiple cracks lie abreast on the surface.

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This paper deals with the two-dimensional thermoelastic contact problem of a rolling rigid roller of specified shape, which induced of friction and heat generation in the contact region, moving with constant velocity in an elastic half-space containing a couple of subsurface cracks. In the present temperature analysis, the speed of the moving heat source is assumed to be much greater than the ratio of the thermal diffusivity and the half contact length. The problem is solved using complexvariable techniques and is reduced to singular integral equations which are solved numerically. Numerical results of stress intensity factors are obtained for the case of two short cracks which are located parallel to the surface. The variance in interference effects on the stress intensity factors with the distance between two cracks, and the effects of the frictional coefficient, the sliding/rolling ratio and the depth of the crack location on the results are considered.

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The propagation rate of fatigue cracking, da/dN, was measured in center-cracked specimens made of 60 Sn/40 Pb solder under cyclic loading conditions at three frequencies (0.01, 0.1, 1.0 Hz). The measured rates were correlated with the cyclic J-integral values, △J-_P-δ calculated from the loaddisplacement hysteresis loops for the solder. The measured crack-propagation rates under the three frequencies were correlated by a line given by da/dN(mm/cycle)=8.5×10^-4[△J-_P-δ(N/mm)]¹.5. To estimate the life of a solder joint by using cyclic J-integral △J_FEM calculated using the elasto-plastic finite element method, a parameter, △J_FEM=4J_FEM which was proposed in other works was used. The parameter, △J_FEM, gave good agreement with △J_P-δ at three frequencies.

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This study is conducted to clarify the influence that the dislocations left over around the fatigue crack have on the propagation rate through the computer simulation of the dislocation dynamics. The computer simulation is based on the equation concerning the elastic interaction of a semi-infinite crack with edge dislocations. The result of the basic analysis shows that the existence of dislocations near the crack-tip suppress the emission of new dislocations. This predicts that the shielding effect owing to the dislocations is one of the important factors which affect the propagation rate of the fatigue crack. Furthermore, the results of the computer simulation show that the transient fatigue crack propagation with the sudden change of the stress intensity factor amplitude can be qualitatively understood from the viewpoint of the change of the shielding effect which is induced by the dislocations left over around the crack.

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Fatigue tests were conducted at both 873 K and room temperature for an alumina-sprayed type 304 stainless steel. In order to clarify the fatigue processes such as cracking and delamination in ceramics-coated stainless steel, surface strain was monitored by using a laser speckle strain gauge during the fatigue test. It was found that the substrate strain was fully reflected on the surface strain unless either crack or subsurface delamination was initiated. The surface strain was found to decrease when the interface delamination was initiated. The cracking in the ceramics layer occurred immediately after the cyclic loading at 873 K. However, the crack in the ceramics layer didn't penetrate into the substrate at both 873 K and room temperature. The final failure was caused by the growth of a substrate-crack newly initiated at the delaminated interface of the substrate.

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Fracture toughness for Mode II of multidirectional Carbon Fiber Reinforced Plastic (CFRP) was investigated using End Notched Flexure (ENF) specimens and the Raman Coating Method. Thin films of PbO were deposited on the surface of the ENF specimens by physical vapor deposition (PVD) as a pretreatment to measure strain by Raman spectroscopy.The distributions of strains near the crack tip of CFRP were measured by Raman spectroscopy.The fracture toughness for multidirectional CFRP in Mode II was determined using these measured strains. The results coincided with those found by the conventional experimental method of ENF specimen and numerical analysis using the Finite Element Method (FEM).

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Delamination along an interface between lead metal and molding resin is one of the main causes of the failure of electronic packeges. Evaluation of mixed mode stress intensity factors (SIF_s) of a crack along the interface is useful for strength evaluation of electronic devices. Large residual stress is often induced along the interface because of the different coefficients of thermal expansion of metal and resin. We performed mixed mode delamination tests of joined end notched fiexure (ENF) specimens and measured residual stress along the interface. The mixed mode delamination criterion including the effect of residual stress was successfully described by the SIF_s for an interface crack. These SIF_s were calculated from the test results using the virtual crack extension method together with the finite element method which we developed for an interface crack under thermal stress. The effects of the mode mixity of the SIF_s and residual stress depend on the combination of materials, and these effects are sometimes very great.

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Effect of stress in passivation films on shift in the threshold voltage of GaAs transistors is analyzed using a finite element method. Stress field devoloped in the transistor structure is analyzed by considering thermal stress and intrinsic stress of thin films. Localized polarization and the stress-induced-charge density devoloped in the transistor structure are calculated by considering both the piezoelectric effect of GaAs and the predicted stress field in the transistor structure. It is possible to quantitatively predict the shift in the threshold voltage of the transistor, which is mainly caused by the passivation-film stress, by integrating the calculated density of the stress-induced charge in the transistor area. The minimum shift of about 0.1V is obtained when the film stress is -50MPa. The predicted shift in the threshold voltage agrees well with the measured result.

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The technique of shot peening is commonly used to increase fatigue limit. However, there are many difficulties in applying it to very high HV steel. To overcome these problems, the authors proposed stress double shot peening. This technique is applied to induction-heated steel (IH steel). The authors further investigated the effect of peening angle on residual stress distribution. The main results are as follows: (a) By double shot peening, residual stress distribution near the surface was markedly improved. (b) By stress double shot peening (δ_pre=1400MPa), very high compressive residual stresses (δ_max=-1972MPa and δ_s=-1774MPa) were successfully introduced in hard steel (HV≓700). (c) Peening angle has little effect on the δ_s. (d) δ_max increased with decreasing peening angles between 90 and 45 degree, and δ_max at 45 degree is the highest one, and it decreased with decreasing peening angle. (e) Depth of compressive residual zone (d₀) decreased with decreasing peening angle.

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In the recent study, one of the authors proposed a simple injection molding method of the fiber reinforced biodegradable composites (FRBC) using the waste of biodegradable fabrics and fibers which result from the process of manufacturing products of textile fabrics. Property change in strength of FRBC molded by the injection method due to the biodegradation was studied in this paper. The molded specimens were biodegraded in soil at 30°C with high humidity (>90%), and static tension and 3-point bending fatigue tests were carried out for FRBC such as the polybutylene succinate (PBS) reinforced by cotton (PBS/CO) at each biodegradation term. Static and cyclic strengths of PBS/CO were higher in comparison with those of PBS at the initial stage without biodegradation, but were decreased drastically with increasing biodegradation. The increase in biodegradability of PBS/CO may be caused by the lack of adhesion between cotton and matrix interface.

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We compared the adhesive strength estimated by the stress-singularity-parameters approach with that measured by the shear debonding test of photoresist patterns on Cu substrates. This comparison shows that the stress-singularity-parameters approach is not capable of consistent estimation over a wide range of adherend sizes. We therefore developed a new method (based on the concept of energy release rate) for evaluating adhesive strength. The method is based on the finite element approach and places an "energy release element" (which mathematically represent the energy release due to debonding) between the interface of the photoresist and the Cu substrate. By using this method to calculate the shear debonding strength of a photoresist, we showed that the calculated strength agrees well with the shear-test-measured-strength. We also found that the stress-singularity-parameters approach is only useful when strains are nearly elastic.

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This paper aims to develop a method for evaluating interface strength of thin films on a substrate of LSI chip. Although several methods have been proposed, plastic deformation and fracture of thin metal film bring ambiguity on the interface strength evaluated by the methods in use. In this study, a sandwich specimen, where the deformation of thin films is tightly constraint by substrate and steel bar, is proposed for preventing the plastic strain and the fracture. The validity is examined by experiments for the interface between copper conductor film (thickness: 300nm) and TaN barrier metal layer (thickness: 50nm) in an advanced LSI. The delamination crack initiates from the free edge of interface where the tensile singular stress field, δ=K_fγ^-λ (δ: stress and γ: distance from the edge), dominates. The criterion for the crack initiation is successfully evaluated as λ=0.08 and K_f=9MPa·m^λ by the results of the proposed experiment and the boundary element analysis.There is little fluctuation of strength among the experiments.

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Through investigations of the deterioration of serviced boilers and through time series investigations involving serviced-size creep rupture tests, it has been verified that damage tends to progress locally in the coarse-grain areas of heat affected zones of welded low-alloy boiler steel ; in other words, void development and interconnection progresses noticeably starting from specific grain boundaries. Focusing on this aspect, a "Maximum Fraction of Voids on the Grain boundary Line Parameter (M Parameter) Method" is proposed here as a new method of evaluating creep damage. Using this method, the authors quantified void-induced damage and summarized its relationship with the Creep Life Fraction(t/t_r). The results showed that a distribution was found along a gentle convex curve. Sensitivity and accuracy comparisons made with the conventional void area ratio method verified that this new method reacts with good sensitivity and produces accurate results pertaining to the consumed service life. In short, this new evaluation method is easier to use than the conventional method and is highly reliable.

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The theoretical analysis method of bonded transversely isotropic piezoelectric dissimilar materials is presented. The interface edge with arbitrary bonding angles under torsion is analyzed in this paper. The case of axisymmetric deformation will be dealt with in the 2nd report. The eigenequation determining the stress singular order, and the stress, displacement and electric displacement fields near the interface edge are deduced in details. The results show that the stress singularity order is dependent of geometry shape of the interface edge, and the mechanical properties of bonded materials only, the piezoelectric constants do not influence the singularity under the torsion condition. However, it is very interesting that the electric displacement near the interface edge also behaves singular, and its magnitude can be described by the same intensity factor as that of the stress field. It should be noted that the piezoelectric constants have no effect on the stress or displacement fields, and only related to the magnitude of the electric displacement field under the torsion condition. Moreover, the result also shows that there exists different composite parameter of bonded dissimilar materials under torsion from that for in-plane problems.

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The axisymmetric interface edge of bonded transversely isotropic piezoelectric dissimilar materials with arbitrary bonding angles under axisymmetric deformation is analyzed theoretically. The eigenequation determining the stress singular order, and the stress, displacement, electric displacement and electrical potential energy fields near the interface edge are deduced in details. The results show that the stress singularity order under axisymmetric deformation is dependent of the piezoelectric and dielectric constants, as well as the geometry shape of the interface edge and the mechanical properties of bonded materials. The electric displacement near the interface edge also behaves singular and its singularity is the same of stresses, while the electric potential energy does not behave singular. All the stress, displacement, electric displacement and electric potential energy can be described by same parameters. Due to the anisotropic properties, the results of bonded transversely isotropic piezoelectric materials can no be degenerated to piezo/isotropic or isotropic/isotropic dissimilar materials. This paper also gives out the theoretical results of an interface edge in axsymmetric bonded piezo/isotropic materials.

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Many studies on two-dimensional joints have been so far carried out theoretically and experimentally. Although, the stress distribution of three-dimensional joints is not so clear as that of two-dimensional joints. Because the calculation for stress distribution in the three-dimensional joints requires a vast computer memory and a fine mesh division. In this study, a boundary element method using Rongved fundamental solution is used for calculating the stress distribution. Three typical models of joints are used for our analysis. Model 1 is a typical joint of three-dimensional joints and is composed of two blocks with different properties. Model 2 has a slanting free side-surface in adjacent four side-surfaces at the vertex. Model 3 has two slanting free side-surface. The characteristics of stress distribution near a vertex of three-dimensional joints were precisely investigated in a spherical coordinate system with an origin at the vertex. Logarithmic plots of the distance from the origin and all of stress components in the spherical coordinate were straight and parallel. Furthermore, the distribution functions for stress intensity of every stress components in the spherical coordinate system were investigated for several material pairs, and those for each model were compared and discussed.

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This work considers the one-dimensional thermoelastic problem in an infinitely long cylinder with free surface subjected to a symmetrically instantaneous heating on the basis of the generalized thermoelastic theories, i.e. the Lord-Shulman and the Green-Lindsay theories. The combined forms of the governing equations of both theories are used. The solution in the Laplace transform domain is derived analytically. In order to obtain the temperature and the thermal stress fields in the cylinder not only for short time but also for long time periods, the inverse Laplace transform is performed by use of numerical technique. The results based on the Lord-Shulman theory are shown graphically. The effects of the thermomechanical coupling and the relaxation time on the temperature and thermal stress are discussed.

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Mechanical behavior of wood subjected to normal-shear combined stress conditions was examined. Wood specimens of rectangular bars of Japanese cypress were cut into those whose long axis coincided with the longitudinal direction. These specimens were loaded and twisted in and around the long axis, respectively, according to the following two loading methods, that is, the proportional deformation loading method and the initially constant loading method which has two loading paths. The obtained results are summarized as follows : (1) When the torsional moment was applied to the specimen slightly, the obtained failure strength tended to be measured larger than the pure normal strength. (2) The failure loci of whole testing data could be expressed by the ellipse formula. (3) The failure loci seemed not to be influenced by the loading method and loading path, although the failure mode seemed to be influenced by the loading path.

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A combined model of molecular dynamics with micromechanics was applied to simulations for low temperature brittleness in a tungsten single crystal. Temperature dependency of fracture toughness in low temperature was a main subject in this research. Fracture toughnesses at 77∼225 K were evaluated in simulations. Evaluated toughnesses showed clear temperature dependency, although there were differences between simulation results and experimental results. Two local stresses in nano-scale at a crack tip were introduced to explain a brittle fracture process. One was a driving force for slip and the other for cleavage. The driving force for cleavage was gradually increased after emissions of dislocations although driving force for slip was saturated, and cleavage was caused by the increased driving force when it reached a critical value. The critical values of the driving forces were not influenced by temperature. It meant that emissions of dislocations was not influenced by temperature but mobility of dislocations controlled the temperature dependency of fracture toughness.

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Cavitation erosion was studied for various types of titanium alloys and for Ti-6 Al-4V with various heat treatments. The erosion resistance is the highest for β type alloy and decreases in order of α+β type alloy and pure titanium (α type). The resistance is macroscopically evaluated in terms of HV²/E (HV : Vickers hardness and E : Young's modulus), but the erosion proceeds depending on the microstructures. Heat treatments changes the microstructure of Ti-6 Al-4V drastically. Therefore, annealing at high temperature produces the large second phase and results in the accerelation of the erosion depth, in spite of low mass loss rate.

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In this study, optimum Mech, -design for shape of press-in contact prevented the turning white damage (crazing damage) on high density packaging printed board was examined. In particular, 'Non-damage' method that was prevented craze around thorough-holes on printed board and has high holding force for the contact was proposed. The main results were as follows ; (1) Conventional contacts caused printed board around through-hole the crazing damage. On the other hand, improved contact it no damage. (2) It was understood that crazing damage on printed board was caused by exfoliation between grass-fiber and epoxy resin. These damage on printed board were distributed into following three regions by loaded stress ; (1) Non-damage region, (2) Pre-damage region and (3) Damage region. (3) Maximum normal stress in improved contact was small stress within the 'Non-damage' region which was caused printed board no damage. (4) Improved contact designed by 'Non-damage' method had high reliability for printed board. Because of increase of area of press-fitting portion, this contact didn't only cause printed board no damage around through-hole but also had high holding for the contact.

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Recent advances in understanding of mechanical bone remodeling have been progressed by computational mechanics approach that allows analysis of structural and functional changes of bone with hierarchical structure under complicated mechanical environment. In this study, a simulation method of trabecular surface remodeling for cancellous bone was proposed using digital image-based finite element model in which mechanical environment at the trabecular level relating to cellular activities could be directly estimated. Morphological changes of trabeculae due to remodeling were simulated based on uniform stress hypothesis, that is, the resorption and formation were accomplished by removal and addition of the voxel elements on the trabecular surface driven by stress nonuniformity. Remodeling simulation of cancellous bone cube under compressive loading was conducted using a digital image-based model constructed based on μCT data from distal canine femur. Simulation results demonstrated that the changes in structural indices of cancellous bone qualitatively corresponded with experimental results, and the proposed simulation method has potential to predict the functional adaptation phenomena in cancellous bone.

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