This study is concerned with a new boundary element method based on the time-stepping scheme and the direct scheme for transient heat conduction problems in anisotropic solids. Mathematical formulations of the boundary element method are presented in detail for two-dimensional transient heat conduction. The reduced differential equations by the authors are transformed into regularized boundary integral equations which involve no integrals to be evaluated in the sense of the Cauchy principal value. Boundary element analysis can be performed by using the standard boundary element method. Computation is started from the initial state, and advanced by a time-marching procedure until the final stage is realized. The proposed solution procedures are applied to some typical examples, and the usefulness of the proposed BEM is demonstrated through discussions of the results obtained.

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As a meshless numerical analysis, particle methods are considered promising in the filed of fluid dynamics and structural analyses. SPH (Smoothed Particle Hydrodynamics), which has been mainly applied to super fast impact or collision problems, is expected to be a more powerful tool for general structural problems such as large deformation and general 3-dim structural problems of complex geometrical objects. However, the fundamental characteristics (accuracy and convergence of solution, effects of time increment and artificial viscosity, etc) of particle methods have not been clarified at all, which causes the fatal limitation of this method. This paper discussed the several numerical properties of SPH by comparing FEM results. It is shown that structural analysis by particle method (SPH) has relatively good accuracy, as well as good numerical convergence and stability in comparison with traditional method (finite element method) and is expected to be a sophisticated tool for a meshless structural analysis.

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This paper suggests a constitutive equation for a two-phase system in consideration of inelastic deformation, that is plastic and creep deformation, to which micromechanical model based on Eshelby's equivalent inclusion method and Mori-Tanaka's mean-field approximation is applied. This equation is expressed in piecewise linear incremental form, which can be easily put in structural analysis such as finite element method. In addition, the yield condition of this system is also developed. To verify this analysis, three numerical examples for SiC/Al unidirectional composites are shown. As the result of this calculation, it is said that this constitutive equation is appropriate.

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The purpose of this paper is to present a numerical analysis method on thermal stresses in a functionally graded material (FGM) plate considering time-dependent inelastic deformation. This FGM plate has a ceramic-to-metal graded microstructure with spherical particles, which is subjected to a unidirectional heat flow through the thickness. The procedure of this analysis is composed of micromechanics and macromechanics. Micromechanics is based on Eshelby's equivalent inclusion method and Mori-Tanaka's mean field approximation, and according to this theory, the constitutive equation for two-phase composite materials subjected to equally biaxial loadings is formulated. This equation deals with inelastic deformation, that is plastic deformation, creep deformation and interfacial diffusion between ceramic phase and metal one. On the other hand, for macromechanics, the classical laminated plate theory is applied and the above constitutive equation is put in this theory. As an example, some numerical results for Al₂O₃/Ni-FGM and shown.

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Many researchers have approximately analyzed the dynamic behavior of elastic solid subjected to large deformation using infinitesimal deformation theory, but few of them investigated the applicability of the infinitesimal deformation solution. In this paper, a simply supported beam under collision of an impactor with various velocities is treated using both an infinitesimal and a finite deformation analyses, the quantitative difference between both results is shown, and the limit of applicability of infinitesimal deformation solution is examined. As numerical calculation, 2-dimensional dynamic FEM combined with Newmark-β method is used, and the finite deformation analysis is carried out by Updated Lagrangian method.

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Control of the sintering defects in metal/ceramic functionally graded materials was examined with the aide of numerical analysis. Warping, cracking and delamination were observed in the sintered bodies of laminated powder mixtures of stainless steel and alumina used as a model system. The causes of the sintering defects were related to the lack of sintering balance of the layers. To improve the sintering balance, larger particles were used for some layers and warping and delamination were suppressed while cracking was not. Sintering behavior of each layer was expressed by a constitutive model for sintering and the deformation of the laminated powder compacts during sintering was analyzed by the finite element method. The analytical results showed warping of the compacts and revealed the internal stress in the layer where cracking occurred. The suppression of warping was also predicted in the analysis and the usefulness of the analysis for the design of functionally graded materials was confirmed.

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The research described in this paper grew from the serendipitous discovery of the TD (Twinning Deformation) effect, which was discovered by the first author. The experiment involved a SMA column (Ti-40.8% Ni-9.9% Cu, diameter 5 mm, length 50 mm) which was plastically deformed into a cosine wave with a peak-to-peak amplitude of 1.9 mm. The cylinder was then compressed from either end. As the compressive force was increased, the column because straighter, until it finally buckled at 19 kN. The buckling load of the curved columns is the same as that of the straight one. In this research, numerical analysis was performed on the distributions of stress and deformation of the SMA beams under compression and the underlying mechanism of the two phenomena was explained. Analysis of the anti-buckling effect involves a theoretical treatment of Non-Euler buckling. One way of explains the buckling mechanism is to consider the moment-deflection ratio as a spring constant. When the spring constant become negative, the column will buckle. The result of this calculation is in good agreement with experimental buckling loads. In analysis of straightening beams, it is assumed that the column had been bent to the shape of a perfect cosine wave from 0 to 2 π. And based on the same calculations as the anti-buckling analysis, the neutral fiber (or structural center) of the curved column was also calculated.

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A shape-memory polymer of polyurethane series can be designed for its glass-transition temperature T_g, beyond which a remarkable change in stiffness may occur, within the range from -30°C to 70°C. A material containing such shape-memory polymer particles, hence, may be also designed for its macroscopic stiffness by adjusting the T_g distribution of particles. This composite material then can be regarded as an intelligent material to macroscopic stiffness. In the present research, micromechanical analysis on the macroscopic stiffness of such an intelligent material is performed by taking into consideration of the T_g distribution of particles. Effects of temperature on the macroscopic stiffness of the material are calculated with respect to various T_g distributions of particles. As a consequence, we can see that the macroscopic stiffness of the material is closely related with the T_g distribution of particles and, especially for the case of bimodal type of distribution, it decreases as a flight of three stairs with increase in temperature.

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Fatigue tests were conducted at both 893 K and room temperature for a zirconia-sprayed type 304 stainless steel. Surface strain was monitored by using a laser speckle strain gauge during the fatigue test to examin the fatigue processes such as cracking and delamination of subsurface layer. Fatigue life of an Atomospheric Plasma Spraying (APS) zirconia-coated specimen was similar to that of a blasted substrate. A cracking occurred in the ceramics layer at the early stage of fatigue failure and the crack penetrated into the substrate. However, substrate-bondcoating interface interfered with the crack penetration into the substrate. In case of a Low Pressure Plasma Spraying (LPPS) zirconia-coated specimen, the fatigue life was longer than that of blasted substrate. The bond coating layer made by LPPS was found to restrain a crack from initiating in the substrate.

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Rotational bending fatigue tests were carried out using ferrite-pearlite steel modified by the WPC process, which is one of the shotpeening processes. To clarify the high cycle fatigue properties, measurements of residual stress and hardness distribution were performed. Fatigue strength of the specimen with a WPC-treated surface was higher than that of an untreated one. This is because (i) the WPC process forms an extremely shallow hardened layer with high compressive residual stress, and (ii) the compressive residual stress generated by the WPC process was very stable under cyclic loading ; after 10⁷ cycles of stress loading, the reduction of compressive residual stress was very small. A comparison with fatigue properties of the specimen hardened by conventional shotpeening was also conducted with special focus on the difference in fatigue strength and fatigue crack initiation behavior.

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Fatigue strength of FRP/metal adhesive joints, these are double lap joints and embedded joints at low temperature, was determined analytically and experimentally. The stress singularity parameters under mechanical and thermal loadings were analyzed for various delamination lengths by FEM analysis. The delamination propagation rates of the double lap joints were measured under mechanical cyclic loadings at room temperature, and the relationship between the measured propagation rates and the analyzed ranges of stress singularity intensity were obtained. Using this relationship, we estimated the fatigue strength of embedded joints, and these estimations coincide well with the measured strength. The experimentally measured fatigue strength and the analytically calculated thermal stresses at low temperature of both specimens show that the threshold range of stress singularity intensity depends on both temperature and thermal stresses.

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It seems to be possible to heat treat the gears having higher fatigue strength with lower distortion by applying newly developed super rapid induction heating and quenching (SRIHQ) technology. In this previous research, rotating bending fatigue properties of S 45 C tempered martensite structure plane specimens heat treated by SRIHQ having shallower hardened layer and higher compressive residual stress were studied, and it was observed that the fatigue strength was not improved due to the fatigue cracks initiation just beneath the shallow hardened layer. In the present research, rotating bending fatigue properties of same specimens with notch (α=2.3) heat treated by SRIHQ were studied. As a result, on the contrary of previous work, much higher fatigue strength was obtained in spite of shallow hardened layer. The compressive residual stress formed at the bottom of notch is extremely high (2000 MPa) due to the effect of stress concentration.

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When surface quenched steel is tempered through usual high frequency induction heating process, the hardened layer possesses a hardness distribution where hardness decreases as approaching the surface. This selective tempering owing to the principal reason of the induction heating process causes the reduction in the compressive residual stress at the surface which decreases the fatigue strength less than that in case of furnace tempering. However, as shown in this study, the above disadvantage of the induction tempering can be overcome if the following appropriate conditions are employed : (i) a low frequency to extend the heating area ; (ii) a low rate of rasing temperature ; (iii) cyclic heating to allow heat transfer to the inside. Using one of these conditions, the hardened layer is uniformly tempered and the remarkable decrease of the compressive residual stress at the surface is prevented. As a result, the fatigue strength of the induction tempered steel is maintained as high as that of the furnace tempered one with the same surface hardness.

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We consider the transient thermal singular stresses of multiple cracking in a W-Cu functionally graded divertor plate due to a thermal shock. 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 plate. The surface layer contains a parallel array of embedded or edge or cracks perpendicular to the boundaries. The thermal and elastic properties of the material are dependent on the temperature and the position. Finite element calculations are carried out, and the transient thermal stress intensity factors are shown graphically.

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In this study, the phase shifting method of moire-interferometry was used to clarify deformation behavior near an interfacial crack tip. In this experiment, a bimaterial specimen of epoxy and aluminum was used. The unwrapped phase distributions obtained by the phase shifting method of moire-interferometry were automatically wrapped and converted to continuous displacement distributions by using image processing. The measured displacement data were used as the input data of the intelligent hybrid method, which was previously developed by the authors. The intelligent hybrid method successfully demonstrated to obtain smooth higher-order quantities such as the stresses and the strain energy density, automatically detecting and eliminating errors and noises in the experimentally measured displacement fields. Furthermore, for the interfacial crack tip, the path independent separated J integrals useful for interfacial fracture mechanics were actually evaluated. The mixed-mode stress intensity factors were also extracted using the component separation method of the J integral.

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The fracture assessment diagram approach is widely used to predict the fracture load or the critical crack size of nuclear components as in the ASME Code Case N-494. In this approach, a proper failure assessment curve must be defined to estimate fracture conditions accurately considering the effect of the thermal aging caused by long term operations. The present work deals with a crack located in the weldment of type 304 stainless steel pipes because of its higher susceptibility to the thermal aging than the base metal. So, the weldment was aged for 20, 000 hours at 400°C simulating long term operations of boiling water reactor (BWR) plants and was served to tests to obtain the mechanical properties of the aged weld metal. Using the stress-strain relationships of the unaged and aged metals, failure assessment curves are developed and compared with each other to make clear the effect of the thermal aging. Also the authors have checked the accuracy and conservatism of the curves stipulated in the R 6 approach and the ASME Code Case N-494 based on the present curve.

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In the framework of mechanics of plasticity plastic instability has been taken up as the onset of ductile fracture. Prediction of ductile fracture begins from the analysis of necking phenomena. Swift's diffuse necking and Hill's localized necking are very famous for assessing sheet formability. However the criteria proposed for necking and shear banding so far have not been useful so much for evaluating ductility. The concept of plastic instability is based on the possibility of multiplicity in deformation under an identical boundary condition. However, unloading cannot be accompanied at plastic instability. While one of us proposed the concept of load instability, which corresponds to the loss of load control where the load is imposed over the value what material can endures. The criterion of load instability was applied for assessing surface ductility in upsetting. It was proved that the criterion gave very good agreement with the experimental results. But, the criterion did not provide enough terms to determine whether ductile fracture occurs or not in the deformation process in question. This paper presents the annexed condition making up for insufficient aspect in the criterion. The condition examines the possibility of both plastic loading and unloading. The criterion supplemented has applicability for assessing ductility limit in almost deformation processes. The correlation between load instability and plastic instability is discussed.

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In 1st Report the criterion of load instability was introduced for assessing the onset of ductile fracture. So far the multiplicity of deformation has been considered to occur at plastic instability. The concept of plastic instability is based on the possibility of multiplicity in deformation rate under an identical boundary condition. However, plastic instability does not assure the coexistence of unloading with continuous plastic loading. Therefore, it does not bring the onset of necking. On the other hand, load instability provides the possibility of coexistence with unloading as long as it occurs after plastic instability. Then, we adopt load instability as a tool for examining ductility. It is very interesting whether the prediction based on the mechanics of plasticity has the ability of evaluation for the effect of hydrostatic pressure upon ductility. Other interest is central bursting in extrusion or drawing, surface ductility in upsetting, the difference of formability between cylinder bulging and sheet stretching, and so on. Their ductility is evaluated associating load instability with plastic instability.

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The authors developed a new testing equipment for studying statically indeterminate fracture mechanics. Its development purpose is to clarify load history-dependency of the collapse load. The equipment has two actuators orthogonalized. The horizontal actuator applies the axial force and the perpendicular one does the bending moment. In the experiment for examining the effect of load hysteresis on the collapse load, both actuators can keep the preceding load to the constant load value, until axial force and bending load reach the theory collapse point. The actuators can apply the following load under the displacement control in the experiment. The performance of the equipment was confirmed by demonstration tests using single-edge notched specimens of SUS 304 steel. The experimental result clarified load historydependency on collapse load in SUS 304 single-edge notched member subjected to combined tension and bending.

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S-S relationships and progressive damage of a glass fabric composite were studied at multi-axial stress state when normal (σ₁ andσ₂) and shear (τ₁₂) combined stresses were simultaneously applied to thin-walled tubular specimens parallel to the material axes. The experimental results revealed that the S-S relationships in both normal directions were represented by two straight lines intersecting each other at their knee points while the S-S curve in shear is curvilinear and convex downward. Initial yielding surface could be represented by quadratic whose bottom is square and the height is given by the shear yielding stress. The Hill's yield criterion is not applicable to predict the non-linear S-S relationships after yielding. The material failure envelope at multi-axial stress state was given by a combination between the maximum stress theory and Tsai-Wu failure criterion.

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Heat wave in elastic material generated by an impulsive heating of the free surface is analyzed numerically in order to clarify the mechanism of a rapid alloying technology. The TVD finite difference scheme is applied for the present study to catch the discontinuous thermal waves clearly. The present numerical scheme is justificable from the results of behavior of heat waves propagated through Al metal. In addition, the propagation of heat wave through a contact boundary between two different metals, Al and Ni, is examined. The numerical results suggest that the possibility of direct contribution of heat wave to the most part of Al-Ni alloy is denied, but complicated variations of temperature are occurred at the interface. These results indicate that analyses including a phase transition phenomenon are required.

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Carbon nitride (C-N) thin films have been prepared by ion-beam-assisted deposition. The correlation of the influence of the Ar ion assist in the tribological properties and microstructure of C-N films were investigated. The ion-beam gas ratio (Ar/N₂ ratio) was changed between 0 and 2. The tribological properties were measured by pin-on-disc type tribotester. The microstructure of the C-N thin films was investigated by X ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The friction coefficients were 0.15-0.20 irrespective of the ion-beam gas ratio and frictional materials. However, the film which formed under condition of Ar/N₂ =1.0 showed excellent wear resistance. It also showed highest hardness of 21 GPa in this experiment. By the XPS analysis and TEM observation, microstructure of C-N thin film changed from amorphous to three dimensional crystalline-like structure by Ar ion adddtion. Consequently, it shows that the addition of Ar ion was very effective for improvement of mechanical properties when C-N thin film was formed by ion-beam-assisted deposition.

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The present paper proposes a new diagnostic tool for the structural health monitoring that employs a Mahalanobis Distance adopted in discriminant analysis. Structural health monitoring is a noticeable technology for aged civil structures. Most of the structural health monitoring systems adopts parametric method based on modeling or non-parametric method such as artificial neural networks or response surfaces. The conventional methods require FEM modeling of structure or a regression model. This modeling needs judgment of human, and it requires much costs. The present method does not require the process of modeling, in order to identify the damage level using the discriminant analysis. This suggest us, this technique is applicable to the health monitoring system, which identifies the damage of the structure, easily. In the present study, we developed the damage identification method using minimum Mahalanobis Distance. We applied this method to identifications of delamination crack of CFRP Plate. As a result, it was shown that this method is effective for identification of damages.

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An infrared stress analysis technique is relatively a new method based on the measurement of infrared radiation emitted from the surface of a cyclically loaded material. The authors applied this method to evaluate the stress concentration factors for several kinds of notches in the previous study. However, some of the measured values were extremely lower than the comparable values calculated by the FEM. In this study, the sources of the difference between experimental results and numerical values are investigated to improve the accuracy of infrared stress analyses. Since the major source was supposed to be the effect of heat conduction in specimens, the numerical unsteady heat conduction analyses are conducted for three types of similar specimens. According to the comparison between experimental results and numerical values, it is found that the stress distributions in similar specimens differ from each other under the same frequency of cyclic loading due to heat conduction in a specimen and the difference in stress among specimens are remarkable below 10 Hz.

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Novel technique for detection of thickness reduction in steel pipe is suggested. Velocity of the longitudinal wave, which propagates along length of the pipe, shows the frequency dependence. When the coherent pulse is launched, the dispersion distorts the received signal, the time reversal signal of which can be used as the excitation signal to receive the original coherent pulse. In this study, we first transmit the broadband pulse, being symmetric in the time domain, in the sound section. The time reversal signal is then used as the inspection signal. If the wall thickness is decreased, the consequent change in the dispersion relation reduces the symmetry of the waveform. After verifying the effectiveness of this method by numerical simulation, we apply it to the steel pipe with thin section. To make it possible to generate and detect the longitudinal wave at arbitrary positions, we use the electromagnetic acoustic transducers.

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