To make effective use of the VCAD-based software for the generation of degenerated hexahedral element models (V-DualGrid) and structural analysis of elastoplastic materials(V-Struct) in complicated engineering applications, a class of complex elements which are constructed by using the low-order convex elements(called child elements) such as 4-node tetrahedra and 5-node pyramids generated by the division of concave elements in V-DualGrid is developed and implemented to V-Struct. The basic idea employed in the formulation of the complex elements is to use an extended B-bar method to enforce the near-incompressibility constraint to the level of the complex elements in order to effectively avoid the so-called volumetric locking occurred in their child elements, and eventually to enable the successful use of the child elements in elastoplastic analysis. Two analyses for benchmark test and an analysis using a FE model generated actually by V-DualGrid are given to show the good performance of the new complex elements.

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Nuclear fuel assembly is installed in the cask with the necessary protective function during fuel transportation. The structural integrity of the fuel rods which constitutes fuel assembly has to be evaluated to ensure the safety even for the cask drop accident. The mechanical properties such as strength, strain hardening properties, and the stress-strain relation of the fuel cladding material, Zircaloy, change significantly during in-reactor service. Such the changes in mechanical properties of the fuel cladding tube play an important role under the impact loading as the cask drop accident condition. Then, the effect of material property on the dynamic response should be clarified. This paper deals with the numerical simulation of the dynamic buckling behavior of fuel rods under the cask drop incident by using finite element simulation code, LS-DYNA. The purpose of this paper is to elucidate the effect of the material property on the dynamic buckling behavior of the cladding tube. First, the constitutive equation of the irradiated Zircaloy is derived. Second, the dynamic responses induced during cask drop accident were obtained from finite element simulations by using the derived constitutive equation. The influences of the mechanical property on the buckling load and absorbed energy are also evaluated. Finally, the detailed buckling process of the high burnup fuel cladding tube is discussed. It is found that the material property has large influences on the dynamic response of the cladding fuel rods. It is thought that the derived constitutive equation is useful for numerical simulation of the spent fuel rods.

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In this paper, a numerical computation of consistent tangent moduli using complex-step derivative approximation (CSDA) is presented, and its applications to finite deformation problems are demonstrated. The consistent tangent stiffness is needed to achieve quadratic convergence in integration for boundary value problems. However, some material models lead to complex formulations of the consistent tangent stiffness that can be difficult to implement. This study shows a simple, robust and efficient numerical approximation of the tangent moduli that can be easily implemented within commercial FE software. Especially, the CSDA is focused on for numerical derivatives. The CSDA is proved to be of second order for suitably small perturbation and does not suffer from inherent subtractive cancellations that limits the accuracy of finite difference approximations, such as the forward Euler method and the central difference method, in floating point arithmetic. The implementation and the accuracy of this approach is illustrated through several numerical examples.

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Effect of casting defects on the fatigue strength of die cast aluminum alloy was addressed through the tension-compression fatigue test and the X-ray CT inspection, which revealed the amount of porosity included in the specimen. Six types of casting condition were employed to examine the effect of different porosity. Most of fatigue crack sources were the pores. The porosity volume fraction was calculated for all specimens from the three-dimensional X-ray CT images. The fatigue limit of each specimen type was estimated from the fatigue test results. The correlations among fatigue limit, porosity volume fraction, Vickers hardness, and dendrite arm spacing were evaluated, and the result showed that the porosity volume fraction most dominantly affected the fatigue limit in the averaged sense.

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An empirical prediction method for the fatigue strength considering the effect of porosity was proposed. We prepared six types of specimen of ADC12 high pressure die cast aluminum alloy, where the casting condition was different to each other, and obtained the S-N curve for each specimen type from the fatigue test. The porosity volume fraction for all specimens was calculated using the X-ray CT images. The image-based finite element analysis was also carried out for all specimens to evaluate the maximum first principal stress corresponding to the nominal stress amplitude in the fatigue test. The maximum stress was referred to as the local stress amplitude, and its ratio to the nominal stress amplitude was defined as the local stress concentration factor. We modified the S-N data by using the local stress amplitude instead of the nominal stress amplitude, and obtained a single master S-N curve. From the statistical investigation, the local stress concentration factor was found to be determined empirically by the porosity volume fraction. The relationship was identified by the least-square approximation. Consequently, we found that the fatigue strength was predicted from the porosity volume fraction via the local stress amplitude and the master S-N curve.

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Fully reversed tension-compression low-cycle fatigue tests controlled by both of total strain and stress were conducted on extruded AZ31 magnesium alloy using smooth round bar specimens in ambient atmosphere at room temperature. The stress-strain hysteresis loops exhibited a characteristic asymmetric shape with a positive mean stress during total strain-controlled fatigue cycle, in comparison with those with a compressive mean strain under stress-controlled fatigue test. The mean stress was associated with the ratio of compressive yield stress and tensile one in the material, which resulted in mechanical twinning in the compressive phase. The fatigue lives obtained from both controlled experiments were nicely described by the Coffin-Manson relationship. From the plastic strain range-life curves, fatigue life under total strain-controlled fatigue test was shorter than that under stress-controlled one because of an effect of tensile mean stress. Fatigue criteria considering the mean stress effect previously proposed were evaluated in terms of fatigue life predictions based on the experimental results. Also, an energy-based model taken into account of plastic and elastic energy density was discussed to predict the fatigue lives obtained from total strain- and stress-controlled fatigue experiments.

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The relationship between the gasket stress and the tightness parameter has been used in the sealing performance evaluation of gaskets using the ROom Temperature Tightness / Hot Operational Tightness Test (ROTT/HOTT) proposed by the Pressure Vessel Research Council (PVRC). A new evaluation method using the gasket strain rather than the gasket stress is proposed in this paper. In the present study, a new test sequence, namely, the Preheated Hot Operational Tightness Test (PHOTT) is proposed in order to cancel the thermal strain of the experimental setup. A testing machine for ROTT, HOTT and PHOTT that continuously controls the gasket temperature up to 450 °C is constructed. The proposed test can be conducted under either stress controlled or strain controlled conditions, whereas conventional tests are conducted under mixed stress and strain conditions with fluctuating temperature. Test results obtained at room and elevated temperature show that the relationship between the gasket strain and the tightness parameter become a unique relationship on the log-log chart. Therefore, calculation of the bolt load for the assembly process and the operational process is expected to be simplified by evaluating the leakage based on the gasket strain. In addition, the proposed evaluation method is applicable to both asbestos and non-asbestos gaskets (compressed sheet gaskets and spiral wound gaskets).

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Ultimate weight reduction and low manufacturing cost are strongly required in the development of next-generation launch vehicles. It is one of effective methods for these purposes to change structural materials from conventional aluminum alloys to composites, such as CFRP (Carbon Fiber Reinforced Plastics). Under these situations, we developed a launch vehicle structure by using CFRP/honeycomb sandwich panels in order to achieve both weight and cost reduction. FEM (Finite Element Method) simulation was utilized to effectively carry out the structural design. Metallic structures are applied for the flanges (joining interfaces between the other structures) in general; however, we used CFRP structures also for the interface flanges for the weight reduction and manufacturing simplicity. The designed CFRP structure was fabricated and a static load test was conducted considering flight loads during actual launch. The strain distribution was obtained by FBG (Fiber Bragg Grating) sensors and three-dimensional displacement was measured by laser tracker as well as normal strain gauges in the limit load test. These measured data were compared with the FEM simulation results and they show good agreement. We will apply these manufacturing, testing, simulation and sensing techniques for the future launch vehicle developments.

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This paper focuses on the stress and the deformation of a thin circular plate, whose surface is loaded by a expanded cool jet. It is well known that the self-excited oscillation of the jet occurs when it impinges on an object and that the surface of the object is cooled. If the object is a thin plate, then it is deformed and vibrated by the jet impingement. In order to clarify the influence of self-excited oscillation on the deformation of the thin plate, the pressure, the temperature, the strain and the deflection on the plate are experimentally measured at the different nozzle-plate spacings. Using the pressure and temperature in the experiment, the deflection of the plate is analyzed by the finite element method. The analytical results are compared with those by experiment.

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Low-density porous materials with a mesoscopic cellular structure exhibit complex mechanical behaviors macroscopically. The strain-rate dependency of plateau stress is one of the materials' characteristics, and it causes difficulties in the mechanical analysis of the behaviors. In this study, the level variation in the plateau stress is analyzed to formulate its strain-rate dependency. This dependency is investigated by performing various material tests under the conditions of quasi-static and dynamic compressions; results of these tests revealed that the dependency can be represented by the phenomenon of over stress. Then, Perzyna's equation is used to simulate the dependency with the concept of structure transformation of cellular materials. The compression tests with various strain-rates are simulated by using the formulated equations for analysing the over stress and structure transformation problems of the materials. Then, it is known that the strain-rate dependency of the plateau stress can be expressed by using Perzyna's equation, and it depends on the phenomenon of the cellular structure.

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In hydraulic turbine runner, unexpected accidents due to fatigue often occur. In this study, in order to clarify fatigue crack growth and closure properties on SCS6 and SC49 used as hydraulic turbine runner over 27 years, fatigue crack growth test under the stress ratio R-constant were carried out using compact tension specimens of both materials. Fatigue crack growth rate and crack closure were measured by means of an unloading elastic compliance method. The results are summarized as follows:(1) Although the stress ratio dependency on the fatigue crack growth rate is found in both materials, the influence is recognized remarkably in SCS6 except for threshold value. (2) Although the threshold stress intensity factor ΔK_th of SCS6 is almost same as that of SC49 when R<0.5, the value of stress ratio of SCS6, when the R-dependency of growth rate disappears, was found to be higher than that of SC49. (3) Fatigue crack growth rates of SCS6 and SC49 could be correlated with the effective stress intensity factor range ΔK_eff, and da/dN-ΔK_eff relationships of both materials agree well in the low and mid growth rate region except for threshold value. In high ΔK_eff, however, the rapid acceleration of crack growth rate due to the change of growth mechanism to cleavage fracture was found only in SC49.

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In the present paper, fracture toughness of interface crack between thin film and substrate is evaluated by inverse analysis using laser ultrasonic waves. The laser beam is irradiated on the substrate which have a thin film on the lower side. The elastic-ultrasonic wave is excited by the laser beam, and it propagates in the transverse direction for the plate. The supersonic wave reflects on the back of monotony, becomes an expansion wave, and reaches the interface. Finally, the interface crack progresses caused by the expansion wave. In the present study, the interfacial stress is estimated by inverse analysis using Laplace-transformed boundary element method. The displacement history on the back-surface of the specimen can be related to interfacial stress by the transfer function. The transfer function can be obtained numerically by 3-dimensional analysis employing boundary element method. The specimens made from SiC substrate and Diamond thin layer are used in the present study. The fracture toughness of the interfacial crack can be extrapolated from the stress distribution in the vicinity of the crack tip. It is confirmed that the interfacial fracture toughness of SiC/Diamond is 0.16J/m² from the present investigation.

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This paper aims at quantitative evaluation of residual strength after thermal shock in ceramics. First, a model predicting the residual strength from Young's modulus or crack density after thermal shock was established using a fracture mechanics approach. Next, thermal shock tests were carried out for porous SiC and soda glass. The residual strength and Young's modulus of both materials after thermal shock were measured. Then, the crack density of soda glass also was estimated by observing residual cracks on the surface. The experimental results were compared with the predictions to verify the validity of the model. The model exhibits good agreement with the experimental results.

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Copper has been used for high power semiconductor package to satisfy thermal radiation performance. However, copper easily deforms and warpage increases during thermal cycle. In this research, warpage increase mechanism of copper package during thermal cycle is clarified using experiment and finite element analysis (FEA). As a result, this phenomenon occurs as a interaction with plastic deformation of copper at low temperature and a stress relaxation due to solder creep at high temperature. Therefore, warpage increases with minimum temperature of thermal cycle increase or maximum temperature decrease. Minimum temperature conditions affect plastic deformation of copper and maximum temperature conditions affect solder creep. In addition, we found this phenomenon is sensitively controlled by the temperature condition. And the results of elasto-plastic FEA that includes plasticity of copper and solder creep deformation agree well with the experimental result under various thermal cycle conditions.

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Cavitation erosion tests using a vibratory apparatus were carried out to study the effects of liquid metal composition and test material of different stainless steels and a high chromium steel. The relative temperature was defined as the percentage between freezing and boiling points. At a relative temperature of 14 °C, the erosion rate is 10 to 12 times larger in various lead-bismuth alloys and 2 to 5 times larger in sodium than in deionized water. When SUS304 was exposed to cavitation in PbBi, the surface was work-hardened 20% harder compared with original surface. In deionized water, SUS304 was work-hardened by 5%. Therefore, we can conclude that higher collapse pressure can be estimated to act on the specimen surface in lead-bismuth, as compared with that in water. The erosion rate of stainless steels depends on hardness and Hirayama's Ni equivalent. Erosion resistance is the highest for SUS304 and decreases in the order, 9Cr-1Mo steel, SUS403.

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Electron backscatter diffraction (EBSD) technique was employed for observing the microstructural change in SUS316 and STS410 due to low-cycle fatigue. Samples of various degrees of strain amplitude and number of cycles were prepared for crystal orientation measurements. The cyclic straining caused local change in crystal orientations and the change was quantified by a parameter called local misorientation. In SUS316, the local misorientation exhibited stripe-like distribution, which emanated from slip deformation. On the other hand, in STS410, network-like distribution was formed. The cell structure which consisted of dislocations brought about the quasi-grain boundaries. Angular distribution of the power spectrum density obtained by Fourier transfer of the local misorientation distribution maps showed the dependency on loading axis. This suggested that it is possible to know the loading direction by the EBSD observation. It was also shown that the degree of fatigue damage could be estimated by the quantification of the local change in the crystal orientations.

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We have been proposed functionally graded material type electromagnetic wave absorbers (FGM type EM wave Absorbers) which have an absorption layer with graded composition distribution for the improvement in absorption performance and material strength. In this paper, we investigate an electromagnetic noise problem of the FGM type EM wave absorbers for a hollow cylinder. The FGM layer which have nonhomogeneity only though the radius is considered to be multilayered absorption layers in which the material properties are homogeneous inside each layer. Incident electromagnetic wave is also assumed an electromagnetic plane wave. Therefore, the approximate analytical solutions of electromagnetic fields in the FGM layer and scatted electromagnetic fields in outer medium of the absorber are derived based on the method of separation of variables and the eigen mode expansion of cylindrical coordinate system. Numerical calculations are carried out for the FGM type EM wave absorbers composed of epoxy resin matrix and conductive titanium oxide particles. The absorption performances are quantitatively evaluated. The effects of material composition and absorption layer thickness on the absorption characteristics are then discussed. In addition, a possibility of the material design on the FGM type cylindrical absorber suitable for the absorption of EM wave and heat dissipation is suggested.

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The previous study employs delamination detection in CFRP laminates using statistical analysis of temperature characteristic of resistance to prevent electrical resistance changes caused by damages of electrical contact at electrodes. A statistical analysis method discriminates the temperature characteristic of resistance of the damaged structure from that of the intact structure. To detect delaminations without learning processes, a new method which compares the electrical resistances at high temperature with those at low temperature is developed here. The new method has applicability to existing structures and can also detect initial defects. The present study employs the new method for detecting delaminations and initial defects in quasi-isotropic-plied CFRP plates. The detection limit of delamination and the effectiveness of detecting initial defects are experimentally investigated, and the effect of electrode damage on the diagnosis is discussed here.

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This paper describes the Young's modulus of thin films for electronic devices measured by a 3-points bending method. Materials tested were rolled copper, electrolytic copper, direct current plated copper and pulse plated copper and liquid crystal polymer films. Young's moduli were calculated from the difference in the slope of the load-deflection line between aluminum substrate and that with the glued film. The direct current plated copper showed the largest Young's modulus among the copper films. The Young's modulus of the pulse plated copper was larger than those of the rolled copper and electrolytic copper. However, the Young's moduli of all the copper films were smaller than that of bulk copper. The difference of Young's modulus of the copper films was discussed in relation to the residual stress and crystal structure of the films observed by EBSP. The Young's modulus of the liquid crystal polymer was smaller than those of the copper films. Anisotropy of the Young's modulus was found in the liquid crystal polymer film, i.e. the injection direction showed the smaller Young's modulus compared with the transverse direction to it.

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Composite pipes with structurally unsymmetric laminated construction show coupled deformations of bending and torsion. That is, those pipes are bended as well as twisted when a bending moment applied. The golf club shaft is subjected to the moment caused by the centrifugal force acting on the club head during golf swing because the center of gravity of a club head doesn't be located on the axis of a shaft. In this study, the possibility to adjust the face angle just before the impact utilizing the structurally unsymmetric laminated golf club shaft, is investigated. By using the designed laminating method called 1.5 turn lapping, a shaft having practical stiffness and strength as a normal golf club shaft, and also having coupled deformations, is manufactured. Through robot and human tests with a golf club assembled with the designed shaft, it is confirmed that the face angle can be changed comparing with the normal shaft and the slice or the hook also can be rectified pertinently.

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To improve the fretting fatigue strength of splined shaft used for compressor of car air conditioner, press-fit joint was combined with the spline joint. Torsional fretting fatigue strength of the combined jointed shaft was evaluated focusing on the effect of press-fit interference which must be secured when the combined joint is applied to the production process. Torsional fretting fatigue strength of the splined shaft was drastically increased by the combination of press-fit. The improvement was achieved by sharing transmitted torque between press-fit and spline. While fretting fatigue failure occurred at the press-fitted part when the press-fit interference was relatively small, the combined jointed shaft had four times higher fatigue strength than the conventional splined shaft. The increase of press-fit interference prevented the fretting fatigue failure and brought further increase of the fatigue strength, since amount of relative slip was significantly reduced by the increase of contact pressure.

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The effects of overload on the threshold stress intensity factor (K_ISCC) for stress corrosion cracks (SCC) in type 304 austenitic stainless steel (SUS304) were studied. Tensile overload was applied to a wedge opening loaded specimen of SUS304, and SCC tests were carried out to determine the resultant K_ISCC. The values of K_ISCC were found to increase with increasing stress intensity caused by tensile overload. Comparison of the effects of tensile overload on K_ISCC of SUS304 and SUS316 revealed that the effects of overload on K_ISCC of SUS304 was smaller than that of SUS316. Both ΔK_th and K_ISCC can be predicted by the similar equation considering the effects of overload.

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In order to clarify the fundamental fatigue strength characteristic of precipitation strengthening type stainless steel:A286, fatigue tests were performed. In the fatigue test, the authors paid attention to the behavior of microscopic fatigue cracks in order to make clear fatigue strength properties more than those with usual fatigue tests. As a result of the fatigue test, the fatigue strength characteristic of A286 became clear as shown below. The crack of a size according to a crystal grain diameter is easy to initiate and propagate by Mode II. Many cracks initiate and propagate even if the stress is around the fatigue limit and the fatigue crack cannot stop, then the cracks coalesce and it becomes longer, and finally results in a failure. This is the reason why the fatigue failures occur even after 10⁷ cycles.

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The fatigue limit of a blunt-notched specimen is dependent on the fatigue crack initiation limit σ_w1. σ_w1 is the propagating limit of the micro fatigue crack at notch root. However, before now no method for evaluating the σ_w1 based on fatigue crack properties had ever been proposed. In this paper, it is suggested that the initial crack size is dependent on the relationship between the application limit of the characteristic elastic field of the notch and the fatigue crack length measured from the notch root. It is also found that when the initial crack size is given, σ_w1 can be evaluated from the threshold stress intensity factor range ΔK_th.

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