The dual reciprocity method has been successfully applied to boundary element analysis of the field problems to which the fundamental solutions are not available or difficult to implement. This paper is concerned with application of the dual reciprocity method to boundary element analysis of quasi-static coupled thermoelasticity. Time derivatives are approximated by a finite difference scheme, and the volume integrals in the boundary integral formulation are evaluated by means of the dual reciprocity method as the boundary-integral form with or without integral points in the domain. A new computer code is developed and applied to a couple of sample problems, whereby the usefulness and the computational aspects of the proposed solution procedure are demonstrated. Although emphasis is placed on the 2-D problems in this study, the present BEM method can be easily extended to 3-D problems.

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A simplified method for estimating the elastoplastic stress and strain distribution on 60°V notch section from a result of elastic analysis was presented. Elastic and elastoplastic analyses of 60°V notched bars and plates subjected to tensile force were carried out by FEM. It was found from these analyses that the distributions on notch section of equivalent strains obtained from equivalent stresses, stress ratios and strain ratios in elastic condition were analogous to those distributions in elastoplastic condition. The proposed simplified method was based on these analogies, the total strain theory and equilibrium condition of axial force. Good estimated results of the stress and strain distribution, the maximum notch strain and the plastic zone size were obtained. The maximum notch strain estimated by the simplified method was also compared with that by Neuber's and Glinka's methods.

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Piezoelectric materials are gradually used in industrial areas from the excellent charactaristics of the mechanical and electrical couplings such as the expectation to reduce stress concentrations by electrical controls. Contrary to this expectation, piezoelectric materials may have some tendencies to develop critical crack growth because of stress concentrations induced by both mechanical and electrical loads. Therefore, it is necessary to study the behavior of stresses and displacements at the vicinity of the stress concentrated region like a cavity or crack as well as a rigid inclusion. In this paper, a two-dimensional electroelastic analysis is performed on a anisotropic piezoelectric material containing elliptical defect under the cases of in-plane load at infinity. General solutions are provided in terms of complex functions, with emphasis being placed on stress concentrations. Several numerical examples are given for both mechanical and electrical loads.

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This paper deals with the stress concentration problem of a dissimilar elastic solid with a spherical cavity under tension. A method of solution is presented for the problem by applying Green's functions for axisymmetric problems of a dissimilar elastic solid. The Green's functions are defined as solutions to the elastic problem of a dissimilar solid subjected to axisymmetric body forces acting along a circle. The principle of the method of solution is to distribute body forces so as to satisfy boundary conditions for a spherical cavity. The problem is formulated by an integral equation with unknown body forces. Performing numerical calculations, influences of the elastic modulas of the dissimilar solid on the stress distributions on the interface and around the cavity are shown.

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FEM is a very powerful method for stress analysis. However, it is still not necessarily easy to obtain the highly accurate values of stress intensity factors or stress concentration factors by FEM. Recently, authors have proposed the non-linear crack mechanics which use the values of strain at a crack tip. In this paper, a method for calculating the highly accurate values of K₁ or K_t by FEM is proposed, based on the usefulness of the stress values at a crack tip or a notch root obtained by FEM.

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By using the method of the analysis of a crack with bridging fibers in unidirectional fiberreinforced composites, which was previously proposed by the authors, the effects of the Young's moduli of fiber and matrix, the volume fraction of fiber, the numbers and locations of the bridging fibers and the frictional shear stress τ at the interface of fiber and matrix on the stress intensity factor of the crack are numerically investigated. The distribution of the reaction forces to the crack surfaces induced by the bridging fibers is also obtained. Based on these numerical results, the possible behaviors of the crack propagation are considered.

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An epoxy matrix of Carbon Fiber Reinforced Plastics (CFRP) was modified using sub-micron Cross-linked acryloNitrile Butadiene Rubber (CNBR) particles to improve the mechanical properties of CFRP. The static tensile strength increased more than 15% in comparison with the strength of unmodified CFRP when the rubber content was 10 wt%. The Young's modulus little changed due to CNBR modification of the matrix. Fracture toughness and fatigue crack propagation resistance under Mode I loading were also improved due to CNBR modification. The impact resistance in the flat-wise direction was improved as well. Fatigue lives under tension-tension loading were significantly extended by CNBR modification at all stress ranges, although the slope of the S-N line of CNBR modified CFRP is almost the same as that of unmodified CFRP. Differences in fractured surface and internal damage accumulation process between two CFRPs were found. Fatigue lives also increased for hole-notched specimens due to CNBR modification.

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The mechanical reliability of flexible printed circuits (FPC) was studied with an attention to the mechanical properties, especially viscoelastic characteristics, of reinforcing and adhesive material. The bending fatigue test was carried out with employing IPC bending test machine and various specimen which contain different mechanical properties. The main results were as follows. (1) Mechanical properties of reinforcing material (super engineering plastics) had an important role on the FPC bending fatigue life. The high toughness of reinforcing material which were high elastic modulus and ductility caused improvement of FPC fatigue life. (2) The two mechanisms in the effect of viscoelasticity of adhesive material on the bending life of FPC were clarified. The fatigue life of FPC could be improved by controlling higher either the storage modulus G' or the loss modulus G" of adhesive material. (3) The new concept in FPC design was indicated in order to improve the mechanical reliability of FPC. Namely, the improvement of mechanical properties and the transformation between strain and heat energy were considered in FPC design.

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The fatigue mechanism of a intermetallic compound TiAl alloy, coated with ZrO₂ and CoNiCrAIY alloy by the plasma spraying, was studied in vacuum at 1073 K using a SEM-servo testing machine. Especially, the mechanism of crack growth in coating layer and the fatigue process near the interface between TiAl substrate and coating layer were observed from the mesoscopic viewpoint. The results indicate that the fatigue strength of coated TiAl alloy and uncoated TiAl alloy are almost similar. The fatigue property of coated TiAl alloy is controlled by the mechanism of mesoscopic crack initiation and growth in coating layer and the fatigue process near the interface with delamination. It was successful for coated TiAl alloy to apply the mesoscopic fracture mechanics to reveal the factor controlling fatigue life.

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To improve the fatigue reliability for non-thermal refining SCM 415 by a gas soft-nitrided. the influence of the surface modification on the fatigue property was experimentally studied. The fatigue properties were enhanced by gas soft-nitrided, and the fatigue limit of the gas soft-nitrided specimens were higher than that of the carburized specimens. Through fractography using SEM, it was found that fatigue crack initiation in a gas soft-nitrided specimen occurs brittle fracture in the super hardening layer in the surface. The improvement in the fatigue strength of a gas soft-nitrided specimens would be obtained by the prevention of crack growth on N-rich ferrite structure in the diffusion layer.

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The effects of molecular weight on mechanical properties of the thermoplastic polyimide are investigated. The specimens which have 4 different molecular weights (MW) ranging from 2.5×10⁴ g/mol to 3.8×10⁴ g/mol are prepared. Young's modulus, tensile strength and Poisson's ratio are determined by the tensile tests. To obtain the fracture toughness. J_IC the multiple specimen method is applied since the crack propagation occurs in a stable manner. Although Young's modulus, tensile strength and Poisson's ratio are almost constant over the range of MW tested, the J_IC increases with the increase of molecular weight. The rib-like pattern and the river-like pattern are observed on the fracture surfaces of lower and higher MW specimen, respectively. These observations indicate that the crazes significantly grow for the specimens with higher MW. This is considered to be the reason for the increase of fracture toughness. The relationship between the fracture toughness and molecular weight is obtained based on Kusy and Turner.

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A new numerical technique for evaluating the stress intensity factor (SIF) of arbitary 3-D crack is proposed in this paper. This method is based on the solution of an elliptical crack in infinite elastic body under Mode I loading. In an elliptical crack, partial SIFs, K_Iσ and K_Iω, are derived by fitting the near tip stress and displacement, respectively, distribution in a certain direction to the definition of SIF in plane strain state. A complete SIF, K_I, is calculated with K_Iσ and/or K_Iω in some arbitrary directions. Because the local front of an arbitary 3-D crack can be approximated by a part of an ellipse, K_I for an arbitrary crack can be calculated approximately by the same technique. These K_I's calculated in some directions include the residual, and need to be evaluated by the value of these residuals. Selected the direction that this value is minimum, a calculated K_I can be optimized. This paper shows some example calculated by this method.

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UHMW-PE has been used as a bearing material in the artificial knee joint. Stress analysis, using FEM, is generally performed to clarify the cause of in vivo wear and delamination. A test machine, of the displacement control type, was designed and built and equipped with a measuring system to obtain accurate test results and the constitutive equation of UHMW-PE. The maximum crosshead speed of the machine is 10⁴ mm/min. Furthermore, it has the capability of determining stress relaxation and strain recovery behavior immediately after performing a tensile test. Interesting properties of UHMW-PE have been obtained using this machine. Also, the constitutive equations for plasticity and viscoelasticity were derived from the experimental results. The equations have strongly nonlinear properties in the mechanical model described in this work. Stress relaxation simulations based on the equation for viscoelasticity have been performed. From this, it was confirmed that the equation is valid.

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Macroscopic deformation of a polymeric material is physically induced by collective evolution of orientation and alignment of its molecular chains. In the present work, we evaluate its deformation behavior from the molecular-level structure by the molecular dynamics simulations. Thermodynamic quantities such as free energy or entropy are key issues on considering the deformation of polymer because crystallization of the internal structure as deformation might produce entropy decrease. Therefore, we computationally calculate the thermodynamic values by the perturbation method within the MD scheme. First, the free energy difference on the structural change between the polyethylene (PE) and the syndiotactic polypropylene (st-PP) is examined. The results show the reasonable high energy barrier between them and the understandable entropy increase from PE to st-PP. Then, we apply it to amorphous polymer of PE constructed by the random walk method under the uniaxial tension. The entropy decrease due to decrease of the internal potential energy is obtained, which is one of the proper features of the polymer.

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With regard to micro evaluation of mechanical properties of solid materials near a surface by means of a scanning acoustic microscope (SAM), scanning an acoustic lens along one direction of a specimen and successively defocussing the lens to the depth direction of the specimen, we obtain X-Z mode image which contains plentiful information about the mechanical properties near the surface, for example : the surface shape of the specimen, distributions of surface wave velocity and so on. Then, it is shown in this paper that we are able to measure surface roughness of the specimen from X-Z mode image data and evaluate deformation induced anisotropy of materials by introducing the fractal dimensional analysis of the X-Z mode image. Therefore, we can expect that practical applications of a scanning acoustic microscope will be more widely expanded in the near future.

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Grain size dependence of magnetic properties is measured for mild steel specimens. The grain size, which as wel as the chemical composition affects the mechanical properties of steel, is required to be evaluated nondestructively in the manufacturing process. The magnetic properties, such as permeability, also depend on the grain size. This dependence can be used for nondestructive evaluation of the grain size. In this study, the permeability, coercivity, residual magnetization, hysteresis loss, and anhysteretic permeability are measured for the steel specimens with various grain size. We found that the permeability, coercivity and the hysteresis loss depend on the grain size, while the residual magnetization is almost independent. This can be attributed to the measurement using the probe with permalloy core, since the saturation magnetization is about one third of that of the steel.

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Fiber optic sensors are expected to be a nerve of composite structures achieving"smart composite structures"which are able to detect their own damage or the changes of their environment. This paper presents some basic properties concerning the bend loss of looped optical fibers with a view to implementing their practical use as fiber optic sensors. Two single mode and one multi mode optical fibers have been investigated by using two light sources of respective wavelengths 633 and 826 nm. The main conclusions are : (1) The bend losses strongly depend on the wavelength of the light source and the type of optical fiber, (2) There is an optimal bend radius corresponding to a maximal sensitivity, (3) Single mode optical fibers can be used as multi points sensor but multi mode fibers cannot, (4) The Marcuse's theoretical formula can simulate experimental results effectively though it is sensitive to input parameters.

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Chemically assisted growth of pit-like flaws, as blunt stress concentrators, is expected to be a realistic model for predicting static fatigue of pristine silica optical fibers, the initial inert strength of which is very high. This study simulates the flaw evolutions under constant stresses using the Hillig-Charles model together with physically valid modifications on a lower limit in the flaw tip radius, where the evolutions of the equivalent semi-elliptical flaws are formulated adequately. When the initial inert strength of a pristine fiber and the ideal (ultimate) strength of silica glass are known, one can estimate the initial shape of the maximum stress concentrators, but not the size. We found from the simulations that the concentrator of the particular initial size, not the maximum size, controls the lifetime of the pristine fiber, where the maximum stress concentrators of different sizes may exit. Importance of curvature dependence of the surface chemical reaction is also noted in lifetime predictions of pristine silica fibers, which has been ignored in Bouten-With model.

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In this paper, Finite Element Method (FEM) is proposed to apply for a real-time parallel control system of connected piezoelectric actuators, assuming an actuator as finite elements, which are mainly used in the computational mechanics field. Conventional control system has necessity to change state equations slightly, depending on the shape of the system or the quantity of the linked members. Meanwhile, FEM is capable of expressing the state of the total system by stiffness equations, and can cope flexibly with lack or disability of constituting members of the system by controlling stiffness matrices. An inverse problem theory, to calculate required electric voltage for obtaining target displacements, is applied to the control analysis of connected actuators. Noncompatible finite element, which allows in-plane bending mode by fewer numbers of elements, is used in the FEM control program to make the real-time control possible. As a result, the possibility of controlling piezoelectric actuators by the newly proposed methodology has been confirmed.

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A simple method for thermal deformation analysis of a honeycomb sandwich construction (HSC), which is used as wall plates of buildings and mirror plates for parabolic antennas, was given. Orthotropic equivalent material properties are given theoretically by calculations with a periodical unit cell of honeycomb core. The theoretical thermal conductivities of the honeycomb core agreed with the value given by an experimental and computational hybrid system with thermal video system. A honeycomb model which has the theoretical material properties doesn't reduce the precision but significantly reduces the time for pre and post processes, and analyses.

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Based on previous works, a new concept of a nondestructive stress measuring system for welded structures was proposed. Firstly, reinforcement of weld is removed. From strain changes on the surface due to removal, distributions of eigenstrain are determined by the inverse analysis. Then, residual stresses are estimated by the elastic FEM (Finite Element Method) analysis by using the determined eigenstrain distributions as anihnitial condition. Toward realization of this concept, applicability of this method was examined by simulations for a butt welded plate with anisotropic eigenstrains along and near a welding line. In a preliminary analysis on an effect of each eigenstrain component on welding residual stresses, it was found that an eigenstrain component in bead direction has a significant influence on producing residual stresses perpendicular and parallel to the welding line. Thus, by separating this dominating component from other two, an accuracy in the inverse analysis can be considerably improved. Further attempt to reduce unknown parameters in the inverse analysis was to approximate eigenstrain distributions by using a series of logistic functions, which proved to have a wide applicability as a curve fitting function form to actual eigenstrain distributions under various welding conditions. Finally, it was shown that welding residual stresses along and perpendicular to welding line in any location of the plate can be evaluated by using the proposed method.

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In this paper numerical solutions of singular integral equations of the body force method are considered when the whole or some part of the crack surfaces are in contact each other. The body force method is used to formulate the problem as a system of singular integral equations. In the numerical solutions unknown body force densities are approximated using fundamental density functions and Chebyshev polynomials. The calculation shows that the present method yields rapidly converging numerical results even when the inclination angle between the crack and the free surface is small. The mode II stress intensity factors are shown when an inclined edge crack is subjected to compressive residual stresses or Hertzian contact loads with varying the inclination crack angle and friction coefficient.

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In this paper, the problem of a crack normal to an interface in two jointed orthotropic plates is studied as a plane problem. Body force method is used to investigate dependence of the stress intensity factor on the material elastic constants. A particular attention is paid to simplifying kernal function, which is used in the body force method, so that all the elastic constants involved can be represented by three new parameters : H_I, H_2I, H₃ for the mode I deformation and H_I, H_2II, H₃ for the mode II deformation. It is found that the effects of the material elastic constants on the stress intensity factors can be expressed by the three parameters, H_I, H_2I, H₃ and H_I, H_2II, H₃, respectively for K_I and K_II. Furthermore, it is also found that the dependence of K_I on H_I, H_2I, H₃ is exactly the same as the dependence of K_II on H_I, H_2II, H₃.

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Based on the elastic basic equations for the special axisymmetric problem, the stress singularity at the interface edge in a composite is analyzed. It is found that the eigen equation to determine the singular order coincides with that of the corresponding plane strain problem, while the singular stress distribution does not coincide. Three composite parameters are required to describe the stress field in the present axisymmetric interface problem, but only two are needed in two dimensional plane problem.

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The fracture initiated near the interface, which is often observed in experiments, as well as that initiated at the edge of the interface is one of the important fracture modes for bonded dissimilar materials. This paper analyzed the stress intensity factors for an edge crack near the interface, by superimposing the singular stress field near the interface edge without crack and the stress intensity for an edge crack in a homogeneous body. The result of numerical analysis confirmed that the theoretical results obtained in this paper are correct and useful.

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Crack initiation and extension characteristics of tension side, view side and compression side of ceramic/metal joints were investigated under cyclic bending loading. Location of cracks and propagations were investigated by SEM and X-ray compositional analysis methods. The stress and strain distribution under cyclic bending loading were investigated by FEM analysis. The results obtained are as follows. (1) Crack initiation occurred at ceramic/interlayer interface at the specimen corner under cyclic bending loading. The unstable fracture occurred from the interface crack. At the 84∼90% of mean strength, crack initiated at ceramic/interlayer interface at the specimen corner. (2) After a main crack occurred many microcracks appeared in order near the main crack region with the increase of maximum stress. Finally they united to the main crack under cyclic loading. The length of crack was increased with increasing maximum stress. The curve slopes of crack lengths versus stresses also increased with increasing maximum stress. Under constant cyclic bending loading, the cracks intermittently grew. (3) At compression side, when the absolute value of maximum stresses were higher than those of tension side, cracks started on the ceramic/interlayer interface and grew up to about 40μm, and finally halted. (4) The crack initiations occurred at the ceramic/brazing filler interface. The location of crack initiation under cyclic bending loading was same as monotonic strength. (5) The crack length increment was decelerated with increasing energy release rate, then increased. The difference of the relationship between crack length increment and energy release rate was less than that of crack length increment and maximum stress. (6) From the FEM analysis, the plastic deformation progressed in interlayer when specimen was loaded and the plastic strain of interlayer left when unloaded. In the interlayer of interface, as compressional plastic strain was constrained by materials around it, tensile residual stresses occured at the compression side at end of unloading. That is why crack initiation occurred in the compression side.

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Environmentally assisted cracking tests were performed using 3.5 NiCrMoV low alloy steel in deionized water containing 100 ppb dissolved oxygen at 333K. Effects of strain rate, strain hold time and superposed vibratory stress on crack initiation and propagation were investigated. Slower strain rate, longer strain hold time and larger superposed vibratory stress enhanced damage and resulted in shorter life. Effect of each factor on the reduction of life was obtained. The crack morphology was transgranular and widened by corrosion.

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In order to restore damaged joint functions, the prosthesis has been widely implanted into the joint part in recent years. However, the biononconformance often occurs after the reimplantation. In this paper, the shape optimization of a hip prosthesis stem in the total hip replacement was investigated using growth-strain method. At first, growth criterion parameters of femur were sought by applying finite element method for the mechanical adaptive growth behavior of femur. By this analysis, the effect of stress shielding on femur inserted with the prosthesis stem was investigated. Then, the optimum shape of the prosthesis stem was created by growing the stem not so as to be occurred the bone resorption on femur. It was found that the stem shape had effects on the bone resorption of femur.

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Total knee replacement changes the shapes of articular surfaces and the condition of cruciate ligaments depending on the type of artificial knee joints. This affects the contact conditions, i.e. contact forces and contact positions between femur and tibia. In order to evaluate and improve the performance of artificial knee joints it is necessary to recognize the variation of contact conditions to which the components are subjected during various motions. In this paper, the contact conditions between two components during gait were calculated using motion analysis, inverse dynamics and non-linear optimization methods on a two dimensional lower limb model, and moreover, a stress analysis on the fixation interfaces of tibial components was performed. Results indicated that differences in the shape of the articular surfaces and the condition of cruciate ligaments made remarkable differences in the contact conditions and stress distributions on the interface. It is generally considered that these differences would affect the loosening of the components and the life of the joints.

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In this study, a device is developed for the measurement and adjustment of resultant graft tension of the anterior cruciate ligament (ACL) reconstructed knee in vitro. This device is attached to the tibial surface at the outer distal end of the drill hole for ACL reconstruction, and measures the graft tension via suture, that is coming from the graft and fixed at one end of the device positioned on the axis of the drill hole, by using strain gages. A hollow bolt-nut pair at the suture fixing end provides a level adjusting mechanism for the initial tension adjustment of the graft. The calibration test showed a good linearity and sensitivity, and the effect of the device is examined through the knee extension test and anterior-posterior drawing test for four human cadaveric knees. The graft tension observed by the device showed the ACL/graft tention characteristics that is consistent with past reports by several authors, and it is confirmed the developed device enables us to study the graft tension under the pratical situation of ACL reconstruction quantitatively.

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