The concepts and formulations for the strong coupling method, the consistent weak coupling method, and the weak coupling methods are provided. The consistent weak coupling method uses the added matrices which are derived from the condensation of the strong coupling finite element formulation. The weak coupling methods include the modified methods, which have been developed to enhance the convergence rate and computational efficiency. The mathematical characteristics of these methods are discussed from the view point of the added matrices. A number of numerical results are presented to investigate the numerical capabilities and computational efficiency of these method.

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Instability of damage in quati-isotropic square laminates subjected to a static concentrated load is numerically studied by using finite element method to disclose the impact damage problem. Two types of damage, only circular multiple delaminations and both circular delaminations and transverse cracks, are modeled by three-dimensional elements. Energy release rate distributions are calculated along the edges of the delaminations to investigate why and how the impact damage is created. The energy release rate distributions obtained shows that the correlation between the transverse cracks and delaminations is crucial. The results with transverse cracks can explain well the structure of impact damage in the experiment.

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X-FEM proposed by Belytschko et al. uses interpolation functions, which can consider singularity and discontinuity of displacement fields near cracks without complex meshes. This method enables to evaluate stress intensity factors (SIF) and solve crack growth problems efficiently in the area of fracture mechanics. This paper describes the calculation condition such as a numerical integration method, nodal properties and etc. to obtain appropriate solutions for two-dimensional elastic problems. Also the method combining X-FEM with the virtual crack extension method is proposed and applied to evaluation of SIF. It was shown that X-FEM with appropriate calculation conditions can perform stress and eigenvalue analysis for structures containing cracks more easily than conventional FEM.

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In the Interval Finite Element Analysis of structure the uncertainties given by the interval are studied within the finite element formulation to determine the sharp bounds of the displacement response. Two approaches namely, the Direct Interval Finite Element Analysis (DIFEA) and the Iterative Interval Finite Element Analysis (IIFEA) are proposed to obtain the sharp solution as much as possible. In DIFEA, each step of the standard FEA, using ordinary real arithmetic, is simply replaced with the corresponding interval arithmetic step. In IIFEA, the interval structural analysis is formulated as a nonlinear optimization problem, while components of the displacement vector as well as parameters of the structural system with uncertainties are dealt as decision variables. A specific component of the displacement vector is considered as the objective function, which is minimized and maximized to obtain the lower and upper bounds. Validation of these methods is tested to the analysis of truss structural systems with uncertainties in nodal coordinates.

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An efficient dynamic finite element method (FEM) for an elastic body with uniform cross-section was developed. In this method, the finite element mesh is generated in such a way that the body to be analyzed is at first sliced into layers with the same thickness and then each layer is discretized in the same way. The computational time and memory can be saved by utilizing the regularity in the mass, viscosity and stiffness matrices and making them repetitive block tridiagonal matrices, which results from the above mesh. A few example problems were solved with this method to demonstrate its effectiveness. This method is also applicable to many other problems, such as thermal and electrical problems.

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This paper presents a dual reciprocity boundary element method (DRBEM) for solving the steady-state heat conduction problems of functionally gradient materials. The functionally gradient material is modeled as an inhomogeneous one where the heat conduction coefficient is a continuous function of coordinates. The integral equation formulation uses the fundamental solution of Laplace differential equation for a homogeneous material, and hence a domain integral arises in the boundary integral equation. This domain integral is transformed into a boundary integral by using a new set of radial basis functions. The details of the proposed DRBEM are presented, and a computer code is developed for two-dimensional problems. Numerical computation is carried out for several examples, the exact solutions of which are available in the literature. Through comparison of the results obtained by the computer code with the exact ones, the potential usefulness of the proposed DRBEM is demonstrated.

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Distinct Element Method, or DEM, is considered practical and applied to many kinds of numerical analysis; however, it requires a lot of calculation time. A new method, which accelerates computation speed by 3.1 to 31 times, is presented in this paper. A pipelined processor architecture is employed to enhance the process of making a list of contact elements, which needs N² calculation cost, where N is the number of elements. In addition, the calculation precision of the processors is reconfigurable, that is, either 32 bit floating or 32 bit fixed point precision can be implemented on a single hardware when to operate. That is achieved by making use of FPGA, or Field Programmable Gate Array, which is a dynamically rewritable logic device. Through experiments, it is confirmed that our method works as was expected, and is effective.

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Ingot annealing is indispensable process for GaAs single crystal to improve its electric characteristics. One of the technical problems of GaAs ingot annealing is the increase of dislocation density during its annealing process which affects the performance of electronic devices. A computer code was developed for dislocation density evaluation of a single crystal ingot during annealing process. In this computer code, the temperatures in a single crystal ingot were used as input data, which were obtained from transient heat conduction analysis of an ingot. A dislocation kinetics model called Haasen-Sumino model was used as the constitutive equation. In this model, creep strain rate was related to the dislocation density, and this model was extended to the multiaxial stress state based on the theory of crystal plasticity. Three-dimensional finite element model was used to take account of crystal anisotropy such as elastic constants and specific slip directions. Dislocation density analyses were performed using this computer code for GaAs ingots of 4-inches diameter, and the time variations of dislocation density and stress and the residual stress after the ingot annealing were obtained by this computer code.

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A special finite element method (FEM) program to analyze three dimensional singular order of bonded dissimilar materials has been developed. It has been found that three dimensional stress singular order can be accurately determined by using this program for both single and multiple singularities. It has been also found that the three dimensional stress singularity of the interface corner of bonded dissimilar materials is different from that for both plane strain and plane stress cases. Three elastic parameters to express the effect of material combination on the three dimensional edge singularity have been also investigated. Based on the analysis by using the special FEM program, iso-counter graphs of the stress singular order at the three dimensional interface corner have been drawn for three typical interface corner models, which can be used as the database for determining the three dimensional singularity of bonded dissimilar materials.

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In this paper, transient thermal stresses in an Al₂O₃-Ni functionally graded material (FGM) plate subjected to through-thickness heat flow have been numerically analyzed under three different mechanical boundary conditions by taking account of time dependent inelastic deformation due to interfacial diffusion between ceramic and metal phases as well as creep of both phases. First, an outline of the analytical method, which consists of micromechanical and macromechanical approaches, is briefly represented. The micromechanical approach stems from Eshelby's equivalent inclusion method and Mori-Tanaka's mean-field approximation, and the macromechanical one is based on the classical laminated plate theory. Second, we have systematically examined the effects of graded compositional distributions and the number of layers on the thermal stresses in the FGM plate in detail.

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This paper deals with numerical solutions of singular integral equations in interaction problems of a square array of rectangular inclusions under longitudinal tension. The body force method is used to formulate the problems as a system of singular integral equations with Cauchy-type or logarithmic-type singularities, where the unknown functions are the densities of body forces distributed in infinite plates having the same elastic constants as those of the matrix and inclusions. In order to analyze the problems accurately, the unknown functions are expressed as piecewise smooth functions using two types of fundamental densities and power series, where the fundamental densities are chosen to represent the symmetric stress singularity of 1/γ^1-λ₁ and the skew-symmetric stress singularity of 1/γ^1-λ₂. Then, newly defined stress intensity factors at the end of inclusions are systematically calculated for various shapes and spacings of a square array of rectangular inclusions in a plate subjected to longitudinal tension

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Effect of shot-peening on fatigue behavior in gigacycle regime was investigated in order to clarify the duplex S-N curve characteristics. A cantilever-type rotating-bending fatigue tests were performed in laboratory air at room temperature using hour-glass-shaped specimen of high carbon-chromium bearing steel, JIS SUJ2. Fatigue crack initiation site was transited from surface on untreated specimen to subsurface of the specimen due to hardening and compressive residual stress with shot-peening in the region of high stress amplitude. On the other hand, no difference in fatigue life controlled by subsurface crack initiation between untreated specimen and shot peening one was observed in high cycle region. It is suggested that the S-N curve corresponding to internal failure mode is an inherent in the material, as compared with that the S-N curve of surface failure mode is affected by surface conditions, environmental conditions and so on. Subsurface crack initiation and propagation behavior were discussed under the detailed measurement of crack initiation area and shape of fish-eye. And also, S-N characteristics of case-hardened material was discussed.

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As a study in a series to investigate the effect of anodized coating on fatigue strength of aluminum alloys, repeated tensile fatigue test was conducted in laboratory air and at room temperature under the stress ratio of 0.01 using smooth plate specimen of A2014-T6 and A6151-T6 with anodized film thickness of 3μm. Fatigue strength of the anodized specimens decreased by 20-30% as compared with those of uncoated one. Decrease of fatigue strength depended on static strength of the tested materials. The fracture of anodized coating film occurred at the critical strain formed by the accumulation of plastic deformation of substrate metal at an early stage of repeated tensile fatigue process and crack was induced in the substrate at the flaw of the anodized film. It was recognized that fatigue life of anodized specimens was quantitatively evaluated by the consideration of cyclic stress-strain response and strain-life fatigue behavior.

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Fatigue crack propagation behaviors of epoxy adhesives under mode I loading were investigated. Unmodified and rubber modified epoxy adhesives (Shell Epikote 828) were used while high strength carbon steel was used as adherends. In order to know the relationship between crack growth and surface conditions of adherends, adherends were treated by three different methods : acetone cleaning only, sulfuric acid and chromic-sulfuric acid treatments. Experimental results revealed that the fatigue crack growth resistance of epoxy adhesives greatly increased due to acid surface treatment of adherends. In all cases of surface treatments, a mixed failure mode was observed. The failure mode transfers from cohesive failure to adhesive failure with decreasing ΔG₁. It must be noted that very interesting phenomena for crack propagation were observed in both cases of sulfuric and chromic-sulfuric acid treatments. When the test was conducted at a constant amplitude of cyclic displacements, the fatigue crack velocity decreased and the crack was arrested once with decreasing ΔG₁ (ΔG₁=70∿80J/m²). However, the crack began to propagate again. Then, the crack finally met the threshold which was appreciably higher than that for acetone cleaning. This phenomenon does not appear under the dry environment as well as in case of acetone cleaning.

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The fracture behaviors of part-through and through-wall cracked pipes were analyzed using elastic-plastic fracture mechanics. The objective is to establish codes and standards for evaluating axially oriented part-through-wall cracks in pipes made of moderately tough materials and subjected to internal pressure. The conditions for leak before break (LBB) of these pipes were estimated. The crack geometry satisfying the LBB conditions was also analyzed and it was found that they are independent of the pipe geometry and mechanical properties. The critical crack length for pressurized pipe was derived based on a unique parameter for elastic-plastic fracture mechanics. Application of this parameter to high-toughness materials compares favorably with existing experimental results.

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Dynamic response of a reservoir crack with fluid leakage at the crack tip is studied by using a two-dimensional fluid-filled crack in an elastic medium, i.e. a rock mass. We use Darcy's law for describing fluid leakage at the crack tip. It is revealed that the eigen angular frequencies become smaller with increasing fluid leakage at the crack tip. It is also revealed that attenuation becomes stronger with increasing fluid leakage. However, for fluid leakage exceeding a certain level, the situation is opposite, i.e., attenuation becomes weaker with increasing fluid leakage. These effects of fluid leakage on the eigen angular frequencies are stronger for the larger interfacial stiffness due to contact between the asperities on the upper and lower crack surfaces. They are also weaker for larger ratio of the crack length to the initial aperture of the crack.

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The fabrication of Ti-Ni shape memory alloy by elemental powders was attempted by using a spark-plasma sintering method that can produce high-density sintered compacts in a very short sintering time. The relations between the fabrication conditions and the microstructures, tensile properties and thermo-mechanical properties of the sintered compacts were investigated. The appropriate sintering temperature that can fabricate the sintered compacts whose relative densities are as high as about 96% was found. The tensile properties of the as-sintered compacts were able to be improved greatly by performing a solution treatment, and the tensile strength and elongation of the solution-treated compact became 570MPa and 6% respectively. The tensile properties of the solution-treated compacts were able to be improved fairly by performing the aging treatment, and the tensile strength and elongation of the aged compact became 750MPa and 6.5% respectively. This result is one of the highest tensile properties that have been reported in powder metallurgy field so far. The solution-treated compacts showed a super-elastic like behavior above 333K. The recovery stresses of the shape memory treated compact and the aged compact after loading of 2% pre-strain at the temperature change from 293K to 353K were around 250MPa. These shape memory treated compacts and aged compacts were well applicable to the shape memory functional elements due to their sufficient shape memory effect and good temperature-response.

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In the present study, improvement of numerical simulation code for the prediction of shock wave rise times developed by Swegle and Grady is carried out using equilibrium (thermoelastic) stress. The thermoelastic stress is obtained from Inside Temperature (IT) method for estimating temperatures in steady shock wave fronts established by Sano and Abe. In addition, use of the artificial viscous stress is limited conditionally in order to examine effects of the real shock viscous stress in our numerical calculation. The results of our improved simulation for 6061-T6 Al shocked below 9 GPa are compared with experimental results, and obtained good agreements. While, the effect of the viscous stress determined from the thermoelastic stress in the present method shows little differences from the Swegle-Grady method.

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This paper deals with a strategy for identification of dynamic pressure distribution applied to the elastic thin plate. Boundary element method is adopted to obtain discretized matrix relation between input loading and output signal, where strain information is used as a supplementary information of the inverse analysis in the present study. Laplace transform and numerical inverse Laplace inversion are introduced in order to treat the dynamic behavior. The coefficient matrix to be solved is given on the Laplace-transformed domain as the form of transfer function relating input and output signals. Since the inverse analysis requires regularization to stabilize the ill-posed solutions, Tikhonov regularization has been employed with singular value decomposition, where the optimal parameter of Tikhonov method was determined by Hansen's L-curve method. Through some numerical simulation on the circular plate subjected to dynamically distributed loading, the usefulness of the present method based on the Laplace-transformed-BEM is demonstrated in detail.

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Fracture tests by hydraulic pressure were performed on corroded and/or artificially flawed closed cylindrical-vessels as well as similar new vessels. Critical pressure for plastic collapse of all the vessels was predicted reasonably by equation that assumed a thin thickness with strain hardening material. When the fracture occurred independent of existing flaws of the vessels, fracture pressure was predicted by the above equation and the values were the same with those for sound vessels. When the fracture originated at flaws of the vessels, fracture pressure was predicted conservatively by an equation that assumed local plastic collapse for an axial surface crack on a cylinder. The results revealed the condition for leak before burst (LBB). Fatigue life of corroded and/or flawed vessels was predicted based on the above results for fatigue crack growth and final plastic collapse evaluated by fracture mechanics. The prediction suggested that corrosion thinning up to one eighth of thickness of vessels was safe, while one up to half thickness could be allowed with careful attention.

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Propagation of the stress wave in a proximal interphalangeal joint during compressive impact loading was analyzed by the dynamic finite element method. The explicit method was used in the analysis and the distribution of stress at each step of the time was evaluated. The maximum principal stress is nearly equal to the minimum one in the articular cartilage and therefore the equivalent stress is very small. The equivalent stress and the principal stress fluctuate with the time in the subchondral bone of the middle phalanx. The concentration of stress is observed there and the maximum principal stress is positive, i.e., tension. The impulsive stress is absorbed when the stress wave travels through the articular cartilage. The relation between the equivalent stress and the impact velocity is dependent on the time and the stress is linearly related to the velocity in a short time after the impact.

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Delamination and wear of Ultra high molecular weight polyethylene (UHMWPE) tibial insert are major problems in total knee arthroplasty. The potential major factor influencing them is a post irradiation oxidative degradation of UHMWPE. The differences of mechanical properties for UHMWPE specimens after irradiation and degradation have been investigated. GUR 1050 processed in air, GUR 1050 in vacuum, GUR 1150 in air, and GUR 1050 with 0.3 weight % Vitamin E in air were accelerated aged for 23 days at the temperature of 80°C in air after gamma irradiation at the dose of 25kGy. Tensile tests were performed at the crosshead speed of (10)³mm/min and 37°C. SEM observations were also performed and the results were evaluated. Results show that UHMWPE samples with additives, such as Calcium stearate and Vitamin E, have superior resistance against oxidation compared with the sample of GUR 1050 processed in air. Particularly, GUR 1050 with Vitamin E showed almost same mechanical properties as virgin (not irradiated) specimen.

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