Error index for stress intensityfactor(SIF)obtained from the results of finite element analysis(FEA)using singular elements was developed by taking advantage of the facts that the functional shape of displacement solution around a crack tip is known and that the SIF can be evaluated only by the displacements. The error index has a dimension of SIF and converges to zero when the actual error of SIF by displacement correlation technique converges to zero. Finite element analyses were carried out for some typical crack problems, including a mixed mode crack, whose analytical solutions are known and the validity of the index was concretely demonstrated through the comparison between the variations of error and index with the sizes of singular element. The degree of error seems to be justly estimated through the value of index.

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The Shore hardness test has been used commonly as a technique of basic hardness measurement. In order to deepen the basic knowledge of the Shore hardness test, the motion of the hammer was numerically investigated using an elastoplastic finite-element method, and was also experimentally studied using a laser doppler vibrometer. By comparing the numerical results with experimental results, it has been clarified that the Shore hardness is significantly influenced by the elastic deformation of the hammer at impact. The efect of deformation of the hammer can be described by the model where the hammer is dealt with a small number of point masses connected by springs in a series. The numerical results show that the impact force increases with increasing hardness of specimens and the force exceeds 1000 times the weight of the hammer.

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To simulate the stress and deformation during the cooling process of fiber-reinforced-plastic(FRP)structures, a finite element method(FEM)to evaluate residual stress and deformation, which occur by cooling after curing of FRP products, has developed. In this method, orthotropic visco-elastic behaviors measured by creep tests at several temperatures were simply approximated with an exponential function and orthotropic parameters. The relaxation modulus approximated with the exponential function describes the visco-elasticity and the orthotropic parameters describe the orthotropy caused by fibers in the FRP. To confirm the performance of the FEM program, the residual stress and defomation of a coil caoted by epoxy GFRP(glass FRP)pre-preg during cooling were simulated with this program. And it is shown that this simulated residual stress agrees well with the experimentally measured stress.

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Nonlinear stress-strain behavior of a unidirectional carbon fiber-reinforced composite AS4/PEEK under various off-axis loading conditions at high temperature was examined with particular emphases on the rate and loading-mode dependence of the response. Monotonic tensile stress-strain curves at high temperature accompanied marked nonlinearity for all off-axis angles except θ=0^○.Permanent strains were clearly observed for all kinds of off-axis specimens after unloading. The off-axis permanent strain remaining after unloading became larger as the applied maximum stress increased. The strain and stress rates have appreciable influences on the flow stress of the off-axis nonlinear stress-strain relationships. These observations indicate that the off-axis nonlinear deformation of this composite involved an irrecoverable inelastic part and it was characterized by a viscoplastic deformation mechanism. In view of these experimental results, a simple micromechanics model for predicting the off-axis rate-dependent nonlinear stress-strain behavior of unidirectional AS4/PEEK was developed using the Aboudi's cell method for homogenizing composite behavior and the Chaboche's viscoplastic constitutive model for describing the rate-dependent inelastic behavior of the matrix material. The primitive calculations using the micromechanics model developed favorably reproduced the off-axis rate-dependent nonlinear behavior for the unidirectional AS4/PEEK at high temperature.

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This paper describes a new numerical integration method for the structural failure probability based on the "Hypersphere Division Method". A hypersphere of a specified radius in polar coordinates is considered and its surface is divided into several finite element meshes at constant step angles of the respective arguments. A failure probability element related to a certain mesh is formulated as the mesh area multiplied by the probability density at the same radial distance and an inedx, one or zero, indicating whether or not the mesh is located in the failure domain. The sum of all the failure probability elements gives the failure probability contribution of the hypersphere. The structural failure probability is evaluated approximately by the sum of the failure probability contribution of several concentric hyperspheres, each radius of which is changed at a constant width within an effective distance range. Numerical examples are presented to illustrate the structural reliability assessment of the proposed method.

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The elastic properties of wood subjected to axial-shear combined stress conditions were 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 proportional deformation loading method and the initial constant loading method. The results obtained are summarized as follows:1)Loading methods had effects on the relationships between apparent shear moduli and conditions of combined stresses. 2)In the case of the initial constant loading method, apparent Young's moduli were influenced by conditions of tension-shear combined stresses. 3)Apparent Young's moduli under compression-shear combined stresses tended to become larger than those under uni-compression, irrespectively of loading method. 4)As for the anisotropy of the apparent elantic moduli, when axial(or shear)stress was mainly applied under axial-torsion biaxial loading, the magnitude of apparent shear(or axial)modulus showed much difference between two(LT and LR) planes of the wood specimen.

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The homogenization method has been developed to evaluate effectively both homogenized material properties and microscopic stress/strain of composite materials. On the other hand, a particle dispersed composite is often used in many industrial field, such as molding resins for electronic packaging. The authors attempted to evaluate equivalent material properties of an elastic modulus and a thermal conductivity of the particle dispersed composite made of an epoxy resin including a silica, in order to estimate the microscopic stress/strain in the next stage. Moreover the validity of the numerical method will be assured with experimental measurements and theoretical rule of mixtures. The equivalent modulus and thermal conductivity are successfully evaluated using the finite element analysis by a framework of the homogenization theory at any volume fractions of filler.

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We analyzed the stress in semiconductor devices manufactured by the 0.25-μm process. This analysis used a finite-element-method, in which we took stress-dependent oxidation into account, to make clear the mechanism of sharpening the upper corner of the isolation structure during thermal oxidation. The corner sharpening occurs because oxidation is suppressed under high compressive stress, which occurs because expansion of newly grown oxide around the upper corner is prevented. To eliminate the sharpening, the oxidation-induced stress must be lowered by controlling the initial shape of the upper corner before oxidation. Further more, because the higher oxidation temperature reduces the stress in the newly grown oxide, it is possible to increase the roundness of upper corner by increasing the oxidation temperature.

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In this study, the theoretical analysis of a control of transient thermoelastic displacement is developed for a rectangular composite plate constructed of a cross-ply laminate and a piezoelectric material due to nonuniform heat supply. By using the exact solutions for cross-ply laminate and piezoelectric plate of crystal class mm2, the theoretical analysis of a three-dimensional transient piezothermoelasticity is developed for a simple supported combined plate. Analysis of a piezothermoelastic problem leads to an appropriate electric potential applied to the piezoelectric plate which suppresses the induced thermoelastic displacement in the thickness direction at the midpoint on the free surface of the cross-ply laminate. Some numerical results for the temperature change, the displacement, the stress in a transient state when the transient thermoelastic displacement is controlled are shown in figures.

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In order to investigate the effect of anodized film on fatigue strength of aluminum alloy, A2014-T6, repeated tensile fatigue test was conducted in laboratory air under the stress ratio, R, of 0.01 using smooth specimen with anodized film thickness of 3μm. Fatigue strength of anodized specimen tested under R=0.01 decreased by 18∼20% as compared with that of the untreated one, even though the anodized film did not affect the fatigue behavior under the rotating-bending fatigue test of R=-1. The anodized film is fractured at an early stage of repeated tensile fatigue process, because it is too brittle to accommodate the substrate metal. Many cracks are induced to initiate at the substrate by flaws of the anodized film. It was pointed out through the study that the fatigue strength of anodized aluminum alloy is controlled by the crack initiation behavior in the substrate induced by the rupture of the anodized film, which is related to the deformation of substrate metal during fatigue process.

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A prediction method for the fatigue life of polymer composites under arbitrary frequency, load ratio and temperature was extended to that of polymer composite structures. The method is based upon four hypotheses:(A)the same mechanism applies to static, creep and fatigue failure, (B) the same time-temperature superposition principle holds for all failure loads, (C)the linear cumulative damage low applies to monotonic loading, and (D)there exists a linear dependence of fatigue failure load upon load ratio. The tensile tests of a bolted joint system for fiber reinforced plastics(FRP joint)under static, creep and fatigue loadings were conducted at various temperatures. The validity of the proposed method and the applicability of the hypotheses for this FRP joint are discussed.

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In order to evaluate the surface irregularity of fatigue fracture surface for A5052 aluminum alloy and S25C carbon steel, an analytical procedure was developed applying a concept of fractal and a hyperbola model of Richardson effect. Main conclusions obtained in this study are summarized as follows;(1)Fatigue fracture surfaces of the present metallic materials have the fractal nature. Especially, the fracture surfaces of S25C carbon steel under stress ratios R=0.1 and 0.5 have the complete self-similarity in wide-resolution range. (2)Geometrical irregularity of the surface is also well evaluated by combining the fractal dimension and additional indices termed as"index of fracture surface nature". (3)Fractal dimension and each index of fracture surface nature were successfully connected to the stress intensity factor range ΔK.

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The fractal dimension(m)is determined by the AE amplitude distribution during the tensile test of fatigued FRPA. The fractal dimension decreases with an increase in the number or cycles at constant stress amplitude. The degradation of resin in microfractgraphs of fatigued FRPA can be quantitatively explained by the fractal dimension. It is found that the normalized fractal dimension correlates not only to the normalized strain energy but also to the normaliged maximum load at the tensile test after fatigue, and that the correlation between the normalized fractal dimension and the normalized strain energy is a little stronger than the one between the normalized fractal dimension and the normalized maximum load.

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In this study, the problems of interference between an oval hole and a crack in an infinite plate subjected to tension were treated. The method of analysis is an approximate method based on the principle of superposition. In this method, the effect of a small crack existing near an oval hole was treated as the effect of internal pressure expressed by a quadratic expression. The interference effects were calculated by using the present method. The coefficient of the quadratic expression were determined through the interference effects between an oval hole and a crack. K_I and K_II values calculated by the present method were sufficiently accurate in the practical use.

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The finite element method(FEM)is useful for the stress analysis and used widely in general. However, it is still not necessarily easy to obtain the highly accurate values of the stress concentration factors and the stress intensity factors by FEM. Recently, a method for calculating the highly accurate values of the stress concentration factors and the stress intensity factors in two-dimensional crack problems has been proposed by H. Nisitani, based on the usefulness of the stress values at a notch root and a crack tip calculated by FEM. This method is called the zeroth node method. In this study, an extension of the zeroth node method to the round bar with a circumferential notch or a crack was made. The extended method was applied to the tensile problems of a round bar with a single circumferential notch, a single circumferential crack, two circumferential cracks or an infinite row of circumferental cracks. As the results, it was confirmed that the extended zeroth node method has the sufficient accuracy in these problems.

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The point where the front of a 3-D crack intersects a free surface is called"corner point". The ordinary crack tip stress singularity of γ^λ with λ=-0.5 has been well known in fracture mechanics. However, with regard to the stress singularity at the corner point there are several theories which have not been clearly accepted. This paper is concerned with the detailed analysis of the stress singularity at the corner point for a through crack and a semi-circular crack under Mode II loading. According to the theories by Benthem and others, not only K_IIbut also K_III has a non-zero value at a corner point which, however, contradicts the stress-free boundary condition of the free surface. The FEM analysis of the present study based on the careful meshing and accurate determination of singularity(λ)answers to this strange question on the corner point singularity. The answer is that although the value of K_III increases as the crack front approaches the corner point, the domain of non-zero value of K_III decreases infinitesimally and accordingly the influence of K_III can be ignored at the corner point. Similarly, the domain of the singular stress field with λ≐̸-0.5 and λ=-0.6∼-0.5 also decreases as the crack front approaches the corner point. These conclusions must be considered when the fracture criterion at a corner point under mixed-mode loading is discussed.

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Thermal singular stress problem for the cracked glassfiber reinforced plastics at low temperatures is considered. The layered composite is made of a layer bonded between two layers of different physical properties, and the surface layers contain the cracks normal to the interfaces. Fourier transforms are used to formulate the problem in terms of a singular integral equation. Numerical calculations are carried out for the cases of the embedded and edge cracks, and the thermal stress intensity factors at different temperatures are shown graphically.

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Electronic devices composed from composite materials are subject to thermal deformation due to environmental temperature change. Thermal deformation caused by the difference in coefficients of thermal expansion of composite materials leads to fatigue failures in micro component. In this paper, thermal strain distribution under thermal cycle test is measured by Moire interferometry, and creep behavior and residual strain of electronic devices are extracted. On the other hand, to evaluate not only the behavior of cross-section but total Devices behavior, measurement of the out-of-plane displacement is tried by applying Moire interferometry.

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In this study we discussed on the connecting reliability of the solder-free electronic parts with an attention to the optimization of forming process, which is decision of cross section shape and manufacturing method. The optimization was carried out with the popular FEM analysis code MSC-MARC. Residual stress on microscopic area of electronic parts was analyzed with the special X-ray stress measurement system which could search stress on microscopic area(150μm×150μm). The results were as follows. (1)The cross section shape having high holding force was determined by the theory of curved beam model. This theory showed that the important design factors were the redius and the thickness of cross section shape. (2)There was a remarkable difference of cyclic bending endurance between two parts manufactured by different method, although the two electronic parts were formed in the same shape. The residual stress induced by the plastic working process was mainly the dominant factor of the bending strength. (3)The high connecting reliability of solderfree electronic parts was obtained by the optimization of forming process that was the design concepts of the cross section shape and the manufacturing process relating to the induced residual stress.

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In the present study, the relation between the plastic and the elastic stress intensity factors, K_p and K_e, for various V-shaped notch problems is studied by using the finite element analysis. Detailed results for mode I under plane stress and plane strain conitions are investigated. Based on the numerical results, it is found that the relation between K_p and K_e is independent of the notch depth and the scale of plastic zone. Also, it is found that values of K^1-λe_p/K^1-λp_e for various notch problems only depend on the notch opening angle γ and hardening exponent n under plane stress and plane strain conditions. This enables one to evaluate the factor K_p for various notch problems without any additional plastic stress analysis.

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To obtain fundamental data on superplasticity of fine-grained α+β type titanium alloys obtained through protium treatment, superplasticity tensile tests were carried out in vacuum, the strain-rate and temperature dependence of elongation and flow stress n fine-grained Ti-6Al-4V alloy were investigated. Then, changes in microstructure after the tensile test were observed using an optical and scanning electron microscope. Coarse-grained titanium alloy was also tested, and compared with fine-grained alloy. Experimental results are as follows:Fine-grained material having a grain size of 1μm to 3μm shows elongation of over 3700% at a testing temperature of 1123 K and 1173K, and a strain rate of 1×10^-3S<-1>. When the maximum elongation of fine-grained material was investigated, the material showed a huge elongation of more than 8008% at a testing temperature of 1123K and a strain rate of 1×10^-3S<-1>. The m-value of fine-grained material is much higher than that of coarse-grained material, with the maximum m-values being 0.80 and 0.64 respectively. These results indicate that it is not easy to occur a necking in fine-grained material. In the observation of structure after the superplasticity tensile test, coarse-grained material did not exhibit grain growth, but fine-grained material did.

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A theoretical method to evaluate the elastic-plastic stress singularity at the interface edge of bonded power-law materials is proposed, based on the interative approach developed in this study. It is found that the elastic plastic stress singularity depends only on the bonding angle and the hardening exponent of the composed material which has the larger hardening exponent. The smaller the hardening exponent is, the stronger the stress singularity becomes, Moreover, the elastic plastic stress singularity disappears when the bonding angle is smaller than 45°. The singularity concides with that of an interface crack when the bonding angle approaches to 180° Through the comparison with numerical results obtained by the elastic-plastic boundary element analysis, it is proved that the interative method proposed in this study is accurate enough and very efficient.

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The structure of a fiber-optic cylinder pressure sensor for automotive engine is optimized. The fiber-optic sensor utilizes bending power loss in the optical fiber. Because a small local in the fiber affects the sensor characteristics and reliability, it is important for sensor design to have the optimized structure. The sensor output is simulated based on analyses of optical power loss and mechanical deformation of the optical fiber. The simulated results show good agreement with experimental results. Using this simulation method, we optimize the sensor structure so as to obtain both good characteristics and high reliability, taking the effect of dimensional deviation into account. We also find that the allowable deviation of the horizontal dimensions of the sensors is ten times larger than the deviation of vertical dimensions.

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In the printed wiring board manufacturing sector, methods are developed to improve the circuit packaging density. The multi-layer printed wiring board manufacturing process is receiving particular attension. In the current manufacture of these boards, the method frequently used is to laminate the core with insulating resin. Photo-etching is generally used to form the holes connecting the circuits of these boards. However, a problem has emerged in that the strength of the substrate decreases due to the insulating resin part as the multi-layers are progressively formed. Thus, it becomes necessary to use FRP for the insulation layer part. Since it is very difficult to etch composites, lasers have been proposed for a new way to drill holes in such materials. By appropriate adjustment of the laser panetration energy, the holes are drilled only in the insulation part, and a technique is proposed to stop the holes using the copper foil forming the circuit. AFRP has been considered a suitable FRP for such laser processing. In the present study, attempts were made to experimentally produce multi-layer boards using AFRP and GFRP for the insulation layer, and the characteristics of blind via holes drilling with a small power laser were investigated.

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