A mismatch of different material properties may cause stress singularities, which lead to the failure of the bonding part in joints. It is very important to analyze a stress singularity field for evaluating the strength of interface in three-dimensional joints. Thermal residual stresses occur in a cooling process after bonding the joints, and the stress singularity for thermal stresses also occurs. In the present study, a boundary element method and an eigen value analysis based on finite element method are used for evaluating the intensity of stress singularity. Three-dimensional boundary element program based on the foundamental solution for two-phase isotoropic body is used. The strength of interface in two kinds of Si-resin specimen with different bonding area is investigated analytically and experimentally. Stress singularity analysis for acting a delamination force to the specimen is firstly carried out. After that, stress singularity field for the residual stresses varying material property in resin with temperature is determined. Combining the stress singularity fields for the delamination force and the residual thermal stress yields a final stress distribution for evaluating the strength of interface. Finally, the strength of interface in three-dimensional joints was determined as 0.0914-0.133 MPa·m^0.68.

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When two dissimilar materials are bonded, thermal stresses develop due to the difference in coefficient of thermal expansion of the materials. In recent years, not only isotropic materials but also anisotropic materials are used for making bonded dissimilar materials. In this study, free-edge stress singularity of bonded dissimilar orthotropic materials under thermal stress loading is investigated theoretically. The thermal stresses show the free-edge stress singularity similar to that under mechanical loading, when the thermoelastic constant stress term is subtracted. Stress distributions on the interface are calculated by using the boundary element method. The value of the order of thermal stress singularity determined by using boundary element results agrees well with the theoretical value obtained by using the characteristic equation. It is shown that the thermal stress singularity disappears for certain ranges of wedge angles of a pair of materials.

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A new concept is proposed to evaluate residual deformation and residual stresses due to welding in a verificational manner. The proposed method is as follows. Displacements are measured through digital image pictures of a weldment before and after the weld and eigen-stains are evaluated by the inverse analysis. Then displacements and residual stresses are estimated by the forward analysis. The outcomes from this method can be directly applicable to subsequent FEM analysis in design.

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Concept of the structural design has been shifted from the design-by-rule to the design-by-analysis in recent years. However, its shift is restricted within non-welded structure fields. A main reason may be due to lack of applicability for conventional stress measuring method to the finite element analysis (FEM) which is widely used in structural design. To solve this problem, the following new concept has been proposed. Displacements are measured through digital image pictures of a weldment before and after weld and eigen-stains are evaluated by the inverse analysis. Then displacements and residual stresses are estimated by the forward analysis. In this study, development of an image processing algorithm is attempted.

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To reduce tensile residual stress in a welded region, we developed a new welding method that applies a water-shower behind the welding torch. When this method is applied to welding of austenitic stainless steel plates, cooling conditions mainly determine how much the residual stress can be reduced. To determine the conditions, we first used FEM to evaluate the effects of interpass temperature on the residual stress. And we found effective conditions for reducing tensile residual stress. To verify the validity of the conditions, specimens welded with or without water shower cooling were manufactured. Residual stresses of the specimens were experimentally measured. It was found that tensile residual stresses were generated on the surface of the welds and those were reduced in the case that the water-shower was applied. These measurement results agree well with the FEM analyses. It can therefore be concluded that the water-shower cooling during welding is appropriate for reducing tensile residual stress in austenitic stainless steel welding.

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Distinctive mechanical behaviors of bolted joints are caused by the helical shape of thread geometry. Recently, a number of papers have been published to elucidate the strength or loosening phenomena of bolted joints using three-dimensional finite element analysis. In most cases, mesh generations of the bolted joints are implemented with the help of sophisticated commercial software. Therefore, the mesh patterns thus obtained are not necessarily adequate for analyzing the stress concentration and contact pressure distributions, which are the primary concerns when designing bolted joints. In this paper, an effective mesh generation scheme is proposed, which can provide helical thread models with accurate geometry in order to analyze such important characteristics as the stress distribution along the helix and the contact pressure distributions on the pressure flank. Using the FE models constructed according to the proposed procedure, it is shown how the thread root stress and contact pressure vary along the helix. Also shown is how the imperfect engagement of the mating threads, around the top and bearing surfaces of the nut, affects the circumferential contact pressure distribution at the nut loaded surface and the axial load distribution along engaged threads.

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In the previous paper, the GN incompatibility is newly defined and a new annihilation term of a dislocation pair due to the dynamic recovery is introduced into an expression of dislocation density. Furthermore, a multiscale model of crystal plasticity is proposed by considering GN dislocation density and incompatibility. However, details of dislocation-crystal plasticity simulation are not given. In this paper, we explain a method of dislocation-crystal plasticity analysis. A finite element simulation is carried out for an f.c.c. single crystal under plane strain tension. It is numerically predicted that micro shear bands are formed at large strain, and sub-GNBs : small angle tilt boundaries are induced along these bands. Furthermore, the annihilation of dislocation pair and the increase of dislocation mean free path characterizing stage III of work-hardening are computationally predicted.

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The effect of honeycomb cell structure with thin film subjected to an axial impact force is studied by FEM, and a quatitative comparison between numerical estimates and experimental results are made and discussed. Numerical simulation shows that for enhancing the energy absorption capability, causing plastic crush of honeycomb cell and penetration of aluminum films simultaneously can be preferable than thickening the cell wall or reducing the size of honeycomb cell. Moreover, reducing the impact force (peak load) technique for honeycomb cell structure is developed and applied to the axial crushing of honeycomb cell structure with thin film ruptures. Based on the numerical results, the experiments on the collapse of honeycomb cell structure with thin film have been carried out under dynamic condition, and it is found that the numerical results agreed well for impact energy absorbed amount and crushing mode.

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This paper has tried to apply the response surface approximate method in the structural optimization techniques to develop aluminum beverage can ends. Geometrical parameters of end shell are selected as design variables. Analysis points in the design space are assigned using an orthogonal array in the design-of-experiment technique. The finite element analysis code is used to simulate the deforming behavior, and to calculate buckling strength and central panel displacement of the end shell under internal pressure. On the basis of the numerical analysis results, the response surface of the buckling strength and the panel growth are approximated in terms of the design variables. By using a numerical optimization program, the weight of end shell is minimized subject to constraints of the buckling strength, the panel growth suppression and the other design requirements. A numerical example on 202 end shell optimization problem has been shown in this paper.

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In this paper, elastoplastic nonlinear behaviors of square tubes with corrugated surface subjected to axial compression are studied by using finite element method. The effect of corrugation is to control the deformation pattern and to decrease the fluctuation in the load-displacement curve for square tubes. It is found from numerical results that the deformation mode corresponding to the corrugation can be classified into axisymmetric mode and non-symmetrical mode, and the axisymmetric mode is classified into progressive crush mode, in which compressive force vibrates with the folds forming one after another, and simultaneous crush mode, in which compressive force increases uniformly. These features are the same as that of the case of cylindrical tubes with corrugation. However, it is more difficult, in square tubes than in cylindrical tubes, for crushing deformation to occur in accordance with the given corrugation because of the existence of corner parts. A mode classification chart is produced for various conbination of wavelength 2λand amplitude a. Also, itis found that the average stress in crushing of square tubes with corrugation is not mostly dependent on the corner radius in approximation.

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Phase-field simulations of Widmanstätten ferrite formation during isothermal austenite-to-ferrite transformation in Fe-C alloys are carried out. The effects of the anisotropy of interfacial properties on the formation process of Widmanstätten ferrite are studied by the regularized gradient coefficient method in order to introduce strong anisotropy of the interface. The results suggest that the lengthening rate of the ferrite plate decreases with increasing interfacial energy because the growth rate to the broad side increases. With the constant interfacial energy at the broad side of the plate, the increase of the strength of anisotropy causes faster tip velocity and the formation of fine tips. Futhermore, simulation results clarified that the realistic morphology of Widmanstätten ferrite plate can be represented by using the regularized gradient coefficient method and that strong anisotropy of the interface is required for the formation of Widmanstätten ferrite plates from allotriomorph ferrite.

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Recently, the non-linear crack mechanics (NLCM) was proposed by one of the authors, which gives a method for predicting the strength of a real object from the strength of specimens under large scale yielding. In the NLCM, the plastic strain at a crack tip obtained by FEM is used as the measure of mechanical severity. In this study, the effect of crack length on the usefulness of NLCM is discussed based on FEM analysis of the strips with a center crack subjected to tension.

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In this study, the J-Integral value was determined by using the caustics method. The diameter of the caustics is measured experimentally by using the CT specimens. The specimen used here is a polycarbonate specimen with different ligament lengths. The craze zone of the crack tip was determined using photoelasticity and the method of caustics. The correlation between the craze extension and the crack growth behavior is investigated by observing the craze patterns occuring in the vicinity of the crack tip.

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When hot glass plates are quenched with cold water, several crack propagation patterns such as straight, oscillating or branching cracks, appear. In the present study, the authors examined the effect of temperature gradient on the crack propagation patterns in quenching glass plates experimentally. The temperature gradient in the glass plate is controlled by the temperature difference between the hot glass plate and the cold bath, and by descending speed into the cold bath. The experimental results show that the crack propagation pattern changes from a straight crack to an oscillating crack, then to a branching crack with increasing temperature difference and with decreasing descending speed. Also crack propagation pattern depends on plate width. Furthermore, the results shows that the crack propagation direction is strongly affected by specimen boundary.

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A new Prony series approximation technique that can determine the coefficients involved in relaxation function in high accuracy is developed. The technique can be applied to various loading conditions because of the principle based on the incremental method. In addition, every coefficient keeps positive value and satisfies smoothness of relaxation spectrum. In order to verify the effectiveness of the proposed technique, the authors obtained a relaxation modulus data by relaxation test, then determined the coefficients of relaxation modulus function. Also, the storage and loss moduli calculated by the technique showed good agreement with data measured by dynamic test. In addition, it is confirmed that the proposed technique can automatically predict and compensate data in high reliability by a smoothing algorithm which can not be measured.

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During operation, different defects initiate and grow in machine components due to fatigue, SCC, etc., and the reliability of components decreases with operating time. The performance and safety have to be maintained by regular and adequate inspection techniques and appropriate treatment. In this study, the applicability of Remotely Induced Current Potential Drop (RICPD) technique to the evaluation of the size of back-wall fatigue cracks was investigated and the possibility of numerical simulation for the RICPD measurements was discussed. Finite Element Method (FEM) analysis for the RICPD measurements on the plate specimen of type 304 stainless steel containing artificial back-wall defects was performed and calculated potential drop changes by FEM simulation for the back-wall defects show good agreement with experimental results. Sizing of back-wall fatigue crack in the plate specimen of type 304 stainless steel with a thickness of 10 mm was performed by the RICPD technique. Comparisons between evaluated and actual depths of back-wall fatigue crack reveal that the RICPD technique can perform accurate maximum depth estimation of back-wall fatigue crack with the error of 0.93%.

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The effect of hydrogen on fatigue crack growth behavior of four stainless steels has been investigated from the viewpoint of martensitic transformation. The crack growth rates in hydrogen-charged SUS304 and SUS316 were accelerated. The crack growth rate in hydrogen-charged SUS316L was slightly higher than uncharged SUS316L. However, the crack growth rate in SUS405 hardly changed in comparison with uncharged specimens. The matensitic transformation on fatigue fracture surface was detected by X-ray diffraction both in hydrogen-charged and uncharged specimens of SUS304, SUS316 and even in SUS316L. However, the fracture surface of SUS316L, in which the crack growth rate was increased slightly by hydrogen, showed less martensitic transformation than that of SUS304 or SUS316. It is presumed that martensitic transformation in the vicinty of fatigue crack tip contributed to the effect of hydrogen on crack growth rate. Fatigue tests of SUS304 and SUS316L, which were pre-strained at -70°C to enhance a martensitic transformation, were carried out to study the influence of hydrogen and martensite on crack growth. Crack growth rate was remakably increased by hydroggen in not only pre-strained SUS304 but also in pre-strained SUS316L. The hydrogen content of pre-strained hydrogen-charged specimen was much higher than unstrained hydrogen-charged specimens due to the increase in martensite through which hydrogen diffuses much easier and faster than through austenite. The slip bands around crack tip in the hydrogen-charged specimens were less and more discrete than that in the uncharged specimens.

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In order to investigate the effects of the substrate post quenching on the fatigue strength of TiN coated steel, the plate bending fatigue test was carried out for two types of specimen one was the specimen whose steel substrate (carbon tool steel, JIS SK 3) was quenched and tempered after TiN coating (specimen CQ), and the other was the conventional type specimen whose substrate was TiN coated after the substate was quenched and tempered (specimen QC). As the result, it was found that the fatigue limit of the specimen CQ was higher than that of the specimen QC. It was considered that the difference of the fatigue limit originated from the difference of the properties of TiN film, because the hardness of both substrates were almost equal and the difference could not be recognized in the fracture surfaces of their substrates. It was confirmed that the adhesive strength of TiN film was dractically improved by the substrate post quenching as reported in our previous studies. Also, on the fracture surface of TiN film of the specimen QC, the columnar structure was recognized more clearly compared with the specimen CQ, and its fracture surface showed the aspect of the aspect of the brittle fracture. From these results, it was indicated that such the changes of the adhesive strength and the microstructure of TiN film were concerned in the improvement of the fatigue strength by the substrate post quenching.

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Ultrasonic fatigue tests have been performed in austenitic stainless steel, SUS 316 NG, in order to investigate giga-cycle fatigue strength of pre-stained materials, i.e. 5, 10 and 20% tensile pre-strains and -20% compressive pre-strain. The pre-strains were applied before specimen machining. The austenitic stainless steels are known to exhibit remarkable self-heating during the fatigue experiment. Therefore, heat radiation method was established by setting fatigue specimens in a low temperature chamber at about -100°C. The self-heating was controlled by intermittent loading condition, which enabled us to maintain the test section of the specimens at about room temperature. The results revealed that the fatigue strength increased with increasing pre-strain levels. Fish eye fracture was observed for -20% pre-strained specimen fractured at 4.11×10⁷ cycles, while the other specimens exhibited ordinary fatigue fracture surface originated from stage I facet on the specimen surface. The increase in fatigue limit was predicted by Vickers hardness, HV, which depended on the size of indented region. The prediction was successful using HV values obtained by the size of the indented region similar to those of the stage I facets.

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Fatigue characteristics of two kinds of magnesium alloys ; AZ92A casting plate and AZ31M rolled plate, in air and in purified water have been investigated. Plane bending fatigue tests were carried out and fatigue crack initiation behaviors were observed successively. In the air, S-N curve for AZ92A was continuous curve type, however, the one for AZ31M was bi-line type with fatigue limit, because it has a non-propagating microcrack at the fatigue limit. In the water environment, the fatigue strength decreased for both alloys. The tendency of degradation was remarkable under long life region and the fatigue limits decreased by about 50% of that in the air. Crack growth tests under push-pull loading were carried out with center notched specimens. For AZ92A, crack growth rates were found to increase with water environment. However, for long crack their growth rates were lower than that in the air because of crack closure by wedge effect of a corrosion product. Such a effect of water environment on crack growth was not much notable for AZ31M.

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Large structures are usually constructed using the conventional low-carbon steel and often contain many kinds of discontinuous cross sections or initial defects. The fatigue cracks commonly initiate at these sites under repeated loadings. So, the estimation of low-cycle fatigue life for the notched components is one of the most important technologies for the structural metals. In this study, the low-cycle fatigue tests were carried out using the smooth round bar specimens and the notched plate ones with the stress concentation factors Kt = 2.43, 3.26 and 4.25. The strains at the notch root were measured over the fatigue tests. The materials used are the hot-rolled low-carbon steel sheets, SM400A and SM490A. On the basis of test results, the method to estimate the strain on the notched structure using Neuber method, Stowell ones and the fatigue life were considered

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By the ultrasonic fatigue test for Al-Si-Cu die-casting, the influence of internal or surface defects on super-long life properties was investigated. The results were as follows : (1) When surface defects were the crack starting points, the S-N curve leveled off around 10⁷ cycles. On the other hand when the defects were internal defects, the S-N curve showed continued degradation as N_f increase. (2) When the crack starting point was an internal defect, ODA (Optically Dark Area) was observed around the crack initiation point after 10⁸ cycles. However, ODA was not observed when the compulsory fatigue was applied for no-break sample that was tested over 10¹⁰ cycles of N_f. This suggests that the incidence of fatigue crack from the defect point or its progress were not recognized. (3) By using the following formula, which compares the relationship between ΔK_CD ∝ (√area) ^1/3 and ΔK_th∝ (√area) ^1/3 based on the √area parameter model, it is possible to explain the breaking or non-breaking phenomenon caused by the casting defect in the super-long life area (over 10⁷ cycles).

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It is usually regarded as a common understanding that fatigue failure would not occur if stress amplitude is kept below the fatigue limit diagram. However, it was shown in this study that fatigue failure occurred in some special cases of variable amplitude loading condition even when stress amplitude was kept below fatigue limit diagram in the case of small-notched specimen. The cause of such a phenomenon was examined using repeated two-step loading pattern. In the case of constant stress amplitude loading, non-propagating crack was formed only at low mean stress region and not formed at high mean stress. In the case of repeated two-step loading pattern in which the first step stress was chosen as R=-1 and the second step stress was with high mean stress, a non-propagating crack was formed by the first step stress. This crack functioned as a pre-crack for the second step stress with high mean stress. Consequently, fatigue failure occurred even when stresses were kept below the fatigue limit diagram of constant amplitude. It was shown that the constant amplitude fatigue limit diagram does not necessarily guarantee the safety in the case of variable amplitude loading.

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This study investigates the stress analysis in a functionally graded material plate (FGP) under Hertz load. The FGP is made of n-layered circular plate, and is analyzed by use of Michell's function. The homogeneous circular plate is treated firstly, a two layered circular plate is analyzed secondly, and the FGP circular plate is discussed. Numerical calculations are carried out, and the effect of the functional gradation of the plate on stress distribution and maximum stresses in the FGP is discussed.

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This paper deals with the transient thermal stresses of a surface layered material due to the sliding contact with changing frictional coefficient. The actual frictional coefficient is given by the experimental results of the sliding-contact test on the bearing-specimen lined with white metal. The temperature and thermal stresses caused by the frictional heat generation in a coated materials are analyzed by making use of Laplace transformation and Duhamel integration. Numerical calculations are carried out for the same conditions of the examples in the sliding contact test. It became clear that the numerical results of temperature agreed well with the experimental results by choosing the proper heat transfer coefficient and the variations of temperature were similar to the change of frictional coefficient. Moreover, the thermal effects on the stress variations are considered by comparing the results of thermal stresses with the results of mechanical stresses.

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This paper presents an analytical solution for an infinite strip having an eccentric circular hole when the strip is subjected to tension at infinity. The analysis is based on the Papcovich-Neuber potential approach and the solution is obtained by the proper combination of harmonic function in integral forms and infinite series. The boundary conditions both on edge of the strip and on the hole are satisfied using the relations between the polar and Cartesian harmonics. The numerical results obtained are compared with those of existing solutions. A detailed stresses around the hole are illustrated for various sizes of the eccentricity and the hole.

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We developed a nondestructive-inspection method for concrete structures by using frequency sweep sound wave. When irradiating sound waves with one frequency produced by a speaker to a concrete wall with a defect, the region between the defect and the concrete surface resonates. Then by irradiating frequency sweep sound wave we can detect defects with arbitrary natural frequency. The vibration of the surface is measured with laser Doppler vibrometer and internal defects are detected based on the vibration. We inspected concrete specimens containing an artificial defect by the present method. As a result, a disk-shaped defect of 200 mm in diameter and 100 mm in depth could be inspected successfully, where the frequency was continuously changed from 1 kHz to 10 kHz while 10 seconds. In addition, we examined the effect of laser scanning velocity to vibration measurement. The scanning velocity should be under 1 m/s when the measuring frequency is 5 kHz to recognize a dominant natural frequency.

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n-type bismuth-telluride thin films are fabricated by flash evaporation method. Effects of hydrogen annealing on the thin films are investigated for potential application in micro thermoelectric devices. The thin films are grown up to 1 μm on a glass substrate by flash evaporation method. The hydrogen annealing is carried out in the temperature range between 200-350°C on an atmospheric pressure. The electrical resistivity and Seebeck coefficient are measured at room temperature. Both the electrical resistivity and Seebeck coefficient are improved by the treatment of hydrogen annealing, then the power factor of the n-type bismuth-telluride thin film reaches 8.8μW·cm-¹·K² at annealing temperature of 350°C. The structure of the thin films, which is composition and crystallinity, is studied by electron probe micro analyzer, and X-ray diffraction pattern, respectively. The composition of bismuth-telluride thin films is relativity constant until higher annealing temperature. The X-ray diffraction patterns indicate that the crystallinity of the thin films is improved as higher annealing temperature.

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Hip fracture is one of the most important topics in geriatric medicine because the number of this injury is increasing rapidly with the population of the elderly people. To clarify the mechanism of hip fracture and investigate the method of fracture prevention, we developed a fall simulation system which considers the boundary conditions at real fall accidents. Firstly, we constructed a pedestrian multibody model and compared the results of the fall simulations by the model with those of the volunteer fall experiment in a literature. The simulation results showed a distribution of fall direction similar to that of the.experimental data. Next we developed a hybrid type simulation model which consists of a detailed finite element model of thigh and hip joint, and multibody model of the other parts of a whole human body. Using the hybrid model we conducted stress analyses of femur neck. The results showed that knee grounding fall caused hip fracture risk higher than the risk by a lateral impact on the greater trochanter. By comparing the regions of stress concentration, we estimated that a knee grounding causes a cervical fracture while a trochanter grounding may cause a trochanteric fracture.

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