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磯部 大吾郎, 廣田 直也
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Generally, force sensors do not have high reliability in their detected values, especially for dynamic forces. We discuss a new methodology to obtain the distribution of impact forces in manipulators, by considering the numerical model of the mechanism. In this research, a prediction system of impact force using the Finite Element Method is developed, based upon the incremental equation of motion considering the volume force generated by the motion. Expression of contact is discussed, in this paper, on two ways; (a) the impulse method and (b) the gap-element method. A sensor output in an experiment and the numerical result are compared. Although further investigation on the impulse time is required, the peak values of the impact force are practically in good agreement.
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奥田 斂
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In this research, we describe parallel numerical simulation method to compute the stress distribution of three-dimensional composite materials with fiber-reinforcements. The fibers are longitudinally surrounded by matrix, and distributed in a cube arrangement. This multi-phase polymer is modeled using hexahedral finite element discretization. The effects of the computation based on parallel CG solver with a preconditioned and the arrangement of reinforcements are discussed.
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割田 真弓, 北村 史郎, 河村 哲也
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Propagation of the sound wave in a three-dimensional closed region is simulated in this study. The numerical method is based on wave equation. Since we intend to apply this numerical method to the simulation in the real concert hall, we adopt reflection condition and absorbing condition on the boundary. As for the former condition, we assume both free-end reflection and fixed-end reflection. On the other hand, we examine the modified equation which is obtained by adding viscous term to the wave equation in order to express the absorption on the boundary. The results are compared with those obtained by ordinal absorbing boundary condition. Using these method, the propagation of the sound wave is computed not only in the simple cubic region but also in a three-dimensional virtual concert hall.
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野口 力, 中山 司
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Finite element analysis of vortex-induced vibration of array of tubes is presented. In this study, composite overlapping meshes are used to avoid remeshing procedure used in ALE method. Encouraging numerical results have been obtained.
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赤羽 秀文, 中山 司
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This paper deals with the numerical analysis of flow around a circular cylinder by the combined use of FEM and the ghost fluid method. The use of the ghost fluid method suggests that a remeshing procedure can be avoided in the computation of fluid-structure interaction problems. Through some numerical tests, encouraging results have been obtained.
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角田 和彦
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The applications of a finite element scheme to three-dimensional incompressible viscous fluid flows are presented. The scheme is based on the Petrov-Galerkin weak formulation with exponential weighting functions. The incompressible Navier-Stokes equations are numerically integrated in time by using a fractional step strategy with second-order accurate Adams-Bashforth scheme for both advection and diffusion terms. Numerical solutions for flow around a circular cylinder up to high Reynolds numbers are presented.
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北村 史郎, 桑原 邦郎
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Many methods to solve incompressible flow field have been developed so far. The scheme proposed by Kuwahara employs the third-order upwind scheme for the convective term, the second-order central scheme for diffusive term with orthogonal uniform mesh. In this scheme, it is easy to reconstruct complex objects into a calculation region because mesh is uniform. However, grid points can not be distributed around objects effectively. Hence, it's difficult to solve the flow field in boundary layers and so on. Building-Cube method (BCM) is one of adaptive mesh generation systems, which is orthogonal uniform mesh locally and unstructured mesh globally. It is also one of domain decomposition methods. On the mesh generated by this mesh system, the most grid points can be mapped near objects and a higher order scheme e.g. third-order upwind scheme, can be applied. In this presentation, incompressible Navier-Stokes equations are solved with the third-order upwind scheme on the mesh generated by BCM. And some calculation results are shown.
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三浦 慎一郎, 馬越 太郎, 谷口 正樹, 角田 和彦
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ALE method is proposed for the moving boundary flow problems in which a fluid-phase is separated from a solid-body with time. In this paper, we apply to the ALE method based on finite element method for around a periodic moving ellictical body. Finite element schemes are Petrov-Galerkin finite element method with exponential weighting functions in space and numerically integrated in time by using a fractional step strategy with second-order accurate Adams-Bashforth explicit differencing for both convection and diffusion terms. Numerical samples are calculated a parallel computing with domain decomposition method by a 4-node PC cluster. Numerical results are discussed C_d, C_l, C_s and St number with various length and width ratio of an elliptical body.
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沼守 崇志, 三浦 慎一郎, 谷口 正樹, 角田 和彦
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In this study, we apply to parallel computing with Java programing Using UDP. Although the UDP is a protocol used for DNS or NFS, UDP is inferior compared with TCP network in connective reliance. We propose the connections method correctly for parallel computing using UDP. Numerical examples are compared by TCP and UDP for 3-d cavity flow problems with various scales.
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上田 整, 安藤 潤平
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In this study, the thermal singular stresses in a elastic half-plane containing a crack perpendicular to the boundary is considered. The half-plane is subjected to a uniform heat flux and a uniform mechanical load, and the temperatures on the crack surfaces and free surface of the half-plane are maintained at uniform temperatures, respectively. The Fourier transform techniques are used to formulate the problem in terms of singular integral equations. The singular integral equations are solved by using the Gauss-Jacobi integration formula. Both the cases of an internal crack and an edge crack are studied. Numerical calculations are carried out, and the effects of the geometric parameters on the temperature-thermal stress distributions and the thermal stress intensity factors are shown graphically.
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伊藤 勝悦
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Transient dynamic stresses around three coplanar cracks in an infinite elastic medium have been solved. Two equual rectangular cracks are placed on either side of a centrally situated rectangular crack so as to allow for geometrical symmetry. A self-equilibrated system of pressure is applied suddenly on the surfaces of the cracks. To solve the problem, two kinds of solutions are superimposed. One is a solution for a rectangular crack in an infinite elastic medium and the other is that for two rectangular cracks in an infinite elastic medium. Unknown coefficients in the combined solution are determined so as to satisfy boundary conditions at the surfaces of the cracks using the Schmidt method. Stress intensity factors are defined in the Laplace transform domain and these are inverted in the physical space with the aid of a numerical method.
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小林 亮, 長谷川 久夫
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This paper investigates on the stress concentration problems of an elastic semi-infinite plate with a rigid circular inclusion under a uniform pressure partially acting on the straight edge. A body force distribution method of solution is presented for the problem by applying the so-called Melan's solution for a point body force acting in an elastic semi-infinite plate. Influences of the depth of inclusion and the width of pressure on stress distributions are shown.
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佐々木 崇至, 長谷川 久夫, 倉茂 道夫
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This paper investigates on the effects of Poison's ratio, especially effects of negative Poisson's ratio, on stress concentrations of an elastic solid circular cylinder with a rigid spherical inclusion under tension. Lakes has shown that there are materials with negative Poisson's ratios. It is said theoretically that values of Poison's ratio may take from ν=-1.0 to ν=0.5.
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土田 栄一郎, 荒居 善雄, 岡本 洋明, 山本 慎一
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In the previous paper, we proposed harmonic displacement potentials method in the thin elastic plate theory. Then we can solve complicated multi-connected domain problems. In this paper, we present an analytic solution for a semi-infinite elastic plate containing an elliptic inclusion under transverse bending at infinity.
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渡辺 一実
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An exact Green's function for radially symmetric waves in a cylindrically anisotropic and inhomogeneous solid is presented. Non-singular behavior at the front of focused wave is found and is anisotropy and inhomogeneity parameters determine the behavior. Time-harmonic Green's function in the case of linear velocity variation shows non-wave nature at lower frequency than a critical one that is also defined by material parameters.
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畑 俊明
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When a sphere is suddenly subjected to an instantaneous axisymmetric heating on its surface, stress waves occur at the surface of the sphere the moment thermal impact is applied. The stress waves in a sphere proceed radially inward to the center of the sphere. The wave may accumulate at the center and give rise to very large stress magnitudes, even though the initial thermal stress should be relatively small. This phenomenon is called the stress-focusing effect. In this paper, we analyze the phenomenon theoretically. The results give a clear indication of the mechanism of thermal stress-focusing effects and clarify the order of singularity of the stress-focusing effects in a sphere.
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須見 尚文
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The object of this article is to study the numerical method for solving two-dimensional transient response of a strip with a central crack subjected to shear stresses acting on the surface of the strip. The characteristic method for two-space variables is employed to solve the problem. The method employs the explicit finite-difference approximations with second order accuracy based on the integration of the characteristic equations along bicharacteristics. Numerical calculations are carried out for the shear stress wave propagations and the stress intensity factor K_<III>, and the results are shown in figures.
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海津 浩一, 徳永 仁夫, 末吉 圭太郎, 池田 清彦
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The thermally tempered glass has strong resistance for the surface crack, because the residual compressive stress exists near the surface of the glass. However, it also has the residual tensile stress in the center of the glass. Fracture behavior of the thermally tempered glass depends on the distribution of the residual stress. We examined the impact fracture behavior of the tempered glass using the Extended Distinct Element Method (EDEM). From numerical results for the normal glass and tempered glass, it is demonstrated that the thermally tempered glass is broken to many pieces by the residual tensile stress.
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芦田 文博, 坂田 誠一郎, 中田 浩幸
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This paper deals with an inverse problem of transient thermoelasticity in a piezoceramic hollow cylinder of crystal class 6mm. It is assumed that the cylinder is poled in the radial direction. An unknown asymmetric heating temperature on the inner surface is inferred from the knowledge of the electric potential thermally induced on the outer surface. The finite difference formulation with respect to a time variable is employed, so that this inverse problem can be solved. Numerical calculations have been carried out for a hollow cylinder of cadmium selenide. Numerical results for the inferred heating temperature are shown in a figure.
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上田 整, 吉元 正樹
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In this paper, the dynamic electromechanical response of a coated piezoelectric strip with a crack under an anti-plane mechanical and an in-plane electric impact loads is investigated. The crack is oriented normally to the interfaces. Based on the integral transform techniques, the present problem is reduced to the solutions of singular integral equations. Numerical calculations are carried out, and the main results presented are the variations of the dynamic stress and electric displacement intensity factors, the dynamic energy density factors versus time as functions of the geometric parameters and electromechanical loads.
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菅野 良弘, 高橋 智
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The purpose of this study is to present a method of material design of functionally graded material (FGM) plate exhibiting the functions of absorption and shield of plane electromagnetic wave under thermal environment. The FGM plate is divided into n homogeneous layers, which have distinct, constant electromagnetic properties, and then the approximate analytical solutions are derived for reflection attenuation and shielding effect. The numerical calculations are carried out for the FGM plate with the graded complex permittivity expressed in the form of power function.
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千葉 良一, 菅野 良弘
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By approximating a stepwise change in microstructure in the direction of compositional change, an analytical technique estimating the effect of the microstructure on thermoelastic problems in functionally graded materials (FGMs) is proposed. At first, the homogenized thermal and elastic properties used in the macroscale problem are obtained by the asymptotic homogenization approach and FEM. The macroscale thermoelastic problem is analytically solved through the use of the homogenized properties. Then, the plane stress approximation is employed to apply 2D homogenization to the microscale thermal stress field, and the microscale thermal stresses are computed by FEM. Numerical calculations are carried out for the case of the FGM plate which consists of ceramic (PSZ) and metal (SUS304) phases varying across the thickness. In the light of fracture and delamination, the distributions of the maximum principal stress are illustrated.
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倉茂 道夫, 澤口 央, 今井 和郎
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Within the framework of the mechanics of fluid-saturated, isotropic, poroelastic materials, we analyzed mechanical responses of a circular cylindrical sample of such a material subjected to axial compression of constant strain-rate. We examined mechanical responses for a wide range of Poisson's ratio, from positive to negative, especially the apparently non-linear behavior due to pore fluid diffusion. It was found that the non-linearity is more remarkable for the smaller Poisson's ratio. The strong non-linearity appeared in a stress-strain curve for the negative ratio. Poisson's ratio apparently depends on time.
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松永 泰弘
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In this study, the vibration control of a TiNi shape memory alloy coil spring under temperature change is described. At first, the results of uniaxial tensile test for the TiNi wire and coil spring are described. By use of the linear model, the stress distributions and load-displacement curves for TiNi coil spring are predicted analytically. The numerical calculations are performed by use of the material constants obtained by the previous tests. At last, the vibration control of TiNi shape memory alloy coil spring under temperature change are discussed.
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大久保 隆志, 西村 文仁
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The transformation and deformation behavior of a polycrystalline shape memory alloy is modeled and simulated based on the inclusion method. The martensitic transformation condition is defined with taking into account the interaction energy among single crystal grains. In this study, the interaction energy is assumed to be calculated from the change in elastic strain energy due to the mismatch strain induced by the martensitic transformation. The inclusion method with cuboidal inclusion is employed to calculate the elastic strain field. Some numerical calculation are shown to explain the effect of the internal stress state on the transformation behavior.
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荒井 政大, 鈴木 春貴, 成田 光裕
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Resonant ultrasound spectroscopy (RUS) is widely used to evaluate the characteristics of small solid specimens like superconductor of a single crystal or anisotropic materials of fiber reinforced composites, for example. The elastic moduli of the solid body can be determined by measurement of the natural frequencies exited by a pair of Piezo-electronic transducer. In this paper, a numerical technique for the determination of the elastic constants in RUS testing is discussed. An alternative evaluation function for the search algorithm of the elastic moduli defined with determinant of the coefficient matrix is suggested here, and boundary element analysis is applied to calculate the eigen value of the 3 dimensional vibration on the solid body. Some numerical simulations for the Si single crystal are conducted to demonstrate the effectiveness of the present method.
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山岸 郷志, 岡崎 正和
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Elastic moduli of a thermal barrier coating (TBC) film fabricated by an Electon-Beam Physical Vapour Deopsition (EB-PVD) process were measured by the Vibration Reed method. An effect of the rotating of the superalloy substrate during the deposition process was also investigated. It was shown that the elastic moduli of the EB-PVD coating were significantly lower than those fabricated by an atmospheric plsma spraying (APS) process. The Physical background on the low elastic moduli was discussed, employing the Eshelby's appraoch.
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先名 一麿, 岡崎 正和, 山崎 康広
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Thermal Barrier Coatings (TBCs) are essential technologies for the advance gas turbine blades. The information for mechanical properties of TBCs is necessary for the design and maintenance. But little information was exposed. In this paper, we examine the microstructure, stability of microstructure systems and mechanical properties of TBC film that is formed by changing various spraying parameters. And we examine the importance of manufacturing process that has an influence on the mechanical properties and soundness of total parts of TBCs.
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小川 和洋, 市川 裕士, 庄子 哲雄
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This paper describes a method for improving the bond strength of the interface between thermal barrier coatings and bond coatings. So far, in order to increase the bond strength and increase the formation of thermally grown oxide (TGO), Ce and Si were added to the bond coating material and a laser remelting technique for the bond coating were developed. As a result, the improved TBC had superior bond strength compared to conventional TBC. For the next step, to further improve coating properties such as oxidation or delamination resistance, a new coating system is suggested. In this study, high energy ball-milled powder was used for plasma spraying. Active nano particles were deposited on the surfaces of the powder. Using milled powder notably changed the thermodynamic properties. And as a result of high temperature exposure tests, it was show that the morphology of oxidation that formed at the interface was different compared to conventional coatings.
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荒井 正行, 岩田 宇一, 水津 竜夫, 谷 和美
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Recently, metal temperature of combustor and blade in a land-based gas turbine is increasing with inlet gas temperature, in order to improve the thermal efficiency. Thus, thermal barrier coating (TBC) technology is applied to the surface of these hot parts for reducing the metal temperature. Advanced TBC materials and its processing technology such as functionally graded TBC and electron beam deposited TBC had been developed for these demands. But, application of these developed TBCs to the actual turbine blade was found to be difficult, because of a high cost of the processing machine and so on. In this study, advanced TBC with vertical crack in the top coating layer (vertical-crack induced TBC) was tried to fabricate by using a combination of conventional thermal spray technology and the special heat treatment. And, the bonding strength between the top coating and bond coating was examined by four-point bending test. As results obtained, the bonding strength of the vertical-crack induced TBC is very higher than one of the conventional TBC. It was found from interfactial crack path observed by optical microscope that the exsistence of the vertical crack is available for relaxation of the coating stress and reduction of interfacial stress.
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市川 裕士, 小川 和洋, 庄子 哲雄
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In refuse incineration power generation plants, increasing the combustion temperature directly improves plant efficiency. However, due to molten chloride corrosion, the combustion temperature cannot be increased. Consequently, protecting of components from molten chloride corrosion is necessary. In this study, MCrAlY coating was proposed as a protective film against molten chloride corrosion. And also the effects of adding elements to CoNiCrAlY were examined. Four kinds of specimens were prepared. One is a standard CoNiCrAlY coated specimen. The others are Mo blended CoNiCrAlY, mechanically milled CoNiCrAlY, and mechanically alloyed CoNiCrAlY with Mo specimens. These coatings were made by low pressure plasma spraying (LPPS). The specimens were exposed to molten chloride corrosion tests in a NaCl-KCl environment. The results show that mechanically alloyed CoNiCrAlY with Mo has excellent corrosion resistantance.
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多田 直哉, 清水 一郎, 金村 恵吾
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Tensile test of a thin notched plate of titanium was conducted on the stage of an optical microscope and the deformation and fracture behavior was observed in situ during the test. In the present study, the notched specimen was sandwiched by two transparent and colorless plates of polycarbonate, which were called "loading plates," and both ends of the specimen were adhered on the inner surfaces of these loading plates. As there is a large difference in linear expansion coefficient between the specimen of titanium and these loading plates of polycarbonate, tensile load is generated by heating them uniformly. Moreover, strain gage was attached on the side of the loading plate and the tensile load was evaluated by the strain and Young's modulus of polycarbonate. As the proposed method of tensile test for thin plates is very simple and, in principle, it is possible to reduce the size of specimen and loading plates, it might be extended to the tensile test for small thin films.
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才本 明秀, 今井 康文, 本村 文孝
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The crack propagation due to a thermal stress induced by a moving heat alog sine-curve is examined numerically and experimentally. The simulated crack path and crack propagation behavior accords well with observation. The ratio of wave amplitude a and wave length Λ of heat locus controles the behavior of crack growth. When a/Λ<0.2, the crack propagates stably. While a/Λ becomes large value, the apparent instablity of growth behavior including acceleration and deceleration of crack propagation can be found both in the simulation and the observation,
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三角 正明, 大久保 雅文, 川嵜 一博
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Relaxation behavior of median value of compressive residual stresses in induction hardened S45C awa recognized to the relative with the Norton Requation of creep, and the stress index and anther coefficient in Norton equation are mutually correlated each other.
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加藤 保之, 冨澤 康太
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発行日: 2004/09/04
公開日: 2017/08/01
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In case of the second irradiation, which is performed at the adjacent position of the first single irradiation, the distribution of internal force (membrane force and bending moment) becomes very complicated, because the residual stress occurs in the neighborhood of the first irradiated position. Hence, the condition for re-yielding on the second irradiation depends on the position of re-irradiation, temperature condition, etc. In this paper, we investigate the distribution of membrane force and bending moment in the arbitrary radial direction and made clear the time that the plastic region spread in the irradiated area. Moreover, the relations between re-irradiated position and temperature-difference when the irradiated area becomes whole plastic are revealed.
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石原 外美, 柴田 博司, 五嶋 孝仁
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発行日: 2004/09/04
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Repeated thermal shock tests were performed using cemented carbides with two different WC grain sizes to study a cyclic crack growth behavior. The results were compared with those obtained by a rotating bending fatigue tests (stress ratio=-1) as well as pulsating fatigue tests in tension at stress ratio of 0.1. The cyclic growth rates under the repeated thermal shock correspond well with those obtained by a rotating bending fatigue tests, however they are faster than those of the pulsating fatigue.
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柴田 博司, 石原 外美, 五嶋 孝仁
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発行日: 2004/09/04
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Effects of the microstructures in a material on the thermal stress during thermal-shock were analyzed using a triangular spring-lattice model which was originally proposed by Sridhar et al, to analyze thermal contraction induced microcracking in single-phase ceramics. In the present study, maximum energies in a spring-lattice model were simulated for modified multi-phase polycrystalline materials with different microstructures. The simulations were carried out for variations of grain size, aspect ratio, and of physical properties of surrounding structures in the multi-phase polycrystalline structure which was observed in cermets. The results show that reductions of thermal stress were predicted by the changes of the geometry of grains and physical properties of surrounding structures.
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森田 聡, 香川 裕之, 久保 司郎
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発行日: 2004/09/04
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Fatigue crack propagation tests were carried out using multiply edge-cracked speciemns. The specimen was machined to have 19 edge notches at intervals of 10mm. The specimen was then fatigue pre-cracked by eccentric tension-compression loading. Four pre-cracked specimens were prepared. Fatigue crack propagation tests for 2 specimens were performed by eccentric tension-compression loading, while those were performed by 4-point bending loading for the other specimens. COnsequently the multiple cracks tend to propagate selectively in the end.
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飯井 俊行, 柴田 健太一, 渡邊 勝彦
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発行日: 2004/09/04
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Simplified method to evaluate the maximum stress intensity factor (SIF) range of an inner-surface circumferential crack in a long cylinder under steady-state thermal striping was presented within this paper. By the method, the desired maximum SIF range can be evaluated with an engineering accuracy once the mean radius to wall thickness raio r_m/W of the cylinder is specified. No transient SIF analysis nor sensitivity analysis for striping frequency is necessary.
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影山 恭平, 飯井 俊行
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発行日: 2004/09/04
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In this paper, we generalized our stress intensity factor (SIF) error index developed for a singular element, which has the dimension of the SIF. By applying the SIF error index, we developed a 3-dimensional finite element analysis system for cracked structures that target SIF error can be specified.
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笠原 直人, 木村 暢之, 上出 英樹
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発行日: 2004/09/04
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Temperature fluctuation from incomplete fluid mixing induces fatigue damages on structures of nuclear components, which should be prevented. For rational analyses of this phenomenon, the authors have developed a thermal stress evaluation method by power spectrum density funcitons. Rationality of the method was validated through application to piping junction modes tests.
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釜谷 昌幸
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発行日: 2004/09/04
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The stress intensify factor (SIF) of a surface crack having an undulated crack front, which was defined using a csine function based on a semi-circular crack, was evaluated by finite element analysis. The average SIF along the crack front is almost the same if the area of crack is the same, although the value decreases slightly as the complexity of the crack front increases. Crack growth simulations were conductd in order to evaluate the influence of crack shape on growth behavior. The undulated front crack tended to become semi-elliptical in shape during growth. Although the undulated front crack takes a relatively small SIF compared with the semi-circular crack, the growth rate was faster.
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緒形 俊夫, 松岡 三郎
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発行日: 2004/09/04
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A series of mechanical properties tests, such as tensile tests, impact tests, fracture toughness tests, and fatigue tests, at room temperature to 4K were mainly conducted on Ti-5Al-2.5Sn ELI and Alloy 718 for liquid hydrogen engine of a launch vehicle. The obtained tensile and fracture toughness properties were a little bit smaller than those reported by NASA and NRIM before, however, the fatigue properties were relatively lower than the data reported so far. Data resulting from the tests were reviewed in detail and published in the form of data sheets. The result shows and effect of microctructure of those mateirals on their mechanical properties at cryogenic tempeatures and the data sheet program on space use materials are introduced.
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由利 哲美, 小野 嘉則, 緒形 俊夫
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発行日: 2004/09/04
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To ebaluate material risk caused by human-error, the notch effects on the fatigue properties of forged Ti-6Al-4V ELI alloy have been investigated at cryogenic temperatures. Smooth and notched specimens with the K_t=1.5, 2 and 3 were prepared. High-cycle fatigue tests were carried out at 4, 77 and 293 K. The 10^6-cycles fatigue strength (FS) of smooth specimen was increased with a decrease of the test temperature. Although FS of each notched specimen at 4K were lower than those of 77K. At 4K, FS of Ti-6Al-4V ELI alloy was decreased with a increase of the K_t value. Fatigue crack initiation sites of the smooth, the K_t=1.5 and the K_t=2 notched specimens were in the specimen interior (internal type fracture). The size of individual facets comprisingthe internal fatigue crack initiation site corresponds to almost the grain size. Therefore, improvement of the fatigue strength of Ti-6Al-4V ELI alloy which show internal type frature at low temperatures requires attaining a smaller area size by grain refining.
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小野 嘉則, 由利 哲美, 住吉 英志, 松岡 三郎, 緒形 俊夫
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発行日: 2004/09/04
公開日: 2017/08/01
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High-cyle fatigue properties were investigated for Ti-5%Al-2.5%Sn ELI alloy with a mean α grain size of 80 μm, which had been used for liquid hydrogen turbo-pump of Japanese-built launch vehicle. The 0.2% proof stress and the ultimate tensile strength of this alloy increased with decreasing temperature. The fatigue strengths at cryogenic temperatures of 4K and 77K do not increase in proportion to increments of the ultimate tensile strength, and come to be lower than that at 293K around 10^7 cycles. Observations by optical microscopy and scanning electron microscopy reveal that fatigue cracks initiate in the specimen interior and grow transgranularly at cryogenic temperatures. At the crack initiation sites, several facet-like structures are formed at cryogenic temperatures, while there are no facet-like structures at 293 K. Since localized deformation occurs at cryogenic temperatures, the subsurface cracks form facet-like structures and are supposed to initiate in the early stage of the fatigue life. As the result, the fatigue strength deteriorates at cryogenic temperatures.
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