The parameter U^* has been introduced by the authors to indicate load paths in a structure. The most serious problem encountered when calculating U^* for actual structures is the high computation time required. In this study, we propose two methods for reducing the time of FEM calculations required to obtain U^* distributions. In the first method, essential terms are extracted from the inverse stiffness matrix and these terms are used to calculate the internal stiffness. In the second method, three independent inspection loadings are applied to each point. In this operation, the multi-displacement condition is converted into the multi-loading condition. An actual structure is calculated using this second method ; the decrease rate in calculation time is over 90 percent.

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With rapid growth of WAN infrastructure and development of Grid middleware, it's become realistic and attractive methodology to construct wide-area cluster-of-clusters using commodity PCs to run computation-demanding applications. Many of existing parallel finite element applications have been, however, developed under the assumption of the execution on single cluster, and those applications require frequent synchronization and communication among processes. There have been few FE applications that can exploit the distributed environment. In this study, we classified FE applications into two types, called tightly coupled applications and loosely coupled applications. Then we ported and exectuted prototype applications of each type on two clusters. For each type of applications, we evaluate the computational feasibility of utilizing cluster-of-clusters. It is important to achieve load balance that compensates the differences in hardware performance for tightly coupled applications, and load balance between program modules for loosely coupled applications.

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It is well known that the fracture toughness of coarse grained materials is usually improved as the grain size is reduced. However, there are different views on the dependence of fracture property of nanocrystalline materials on the grain size. In this study, we evaluated the influences of grain size on the crack growth behavior in nanocrystalline Fe by the use of Molecular Dynamics (MD) simulations. In order to treat the crack growth in the complicated material, it is important to employ an accurate interatomic potential and a large simulation model which contains many atoms. Here we use the hybrid potential method which combines both accuracy and computational costs by switching interatomic potentials according to the local atomic structure. The crack growth resistance is estimated at two different deformation speeds by the use of crack opening angle. It is revealed that the resistance increases as the grain size is reduced in the case of slower deformation speed. In contrast, the resistance decreases as the grain size is reduced in the case of faster deformation speed. We also show that the grain size dependence of the fracture property is closely related to the shape and size of non-crystallized region which appears around crack tip.

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A virtual crack closure-integral method (VCCM) for quadratic tetrahedral finite element that can evaluate the three-dimensional stress intensity factors under mixed mode loading conditions is presented. Present VCCM formulation can handle arbitrary shaped three-dimensional cracks. In the evaluations of the energy release rates and the stress intensity factors, nodal force and displacement data that are the results of finite element computation are used. Present VCCM is quite simple to implement as a post-processing program for finite element softwares. In this paper, the formulation of present VCCM is described in detail and some numerical results are presented. The numerical results are in good agreement with the analytical solutions. Finally, as a demonstration, a problem of three-dimensionally curved crack is presented.

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In this study, the theoretical analysis of a transient piezothermoelastic problem is developed for a symmetrical functionally graded piezoelectric slab containing a center crack parallel to the free boundaries under thermal shock loading conditions. It is assumed that initially the medium is at the uniform temperature and is suddenly subjected to a uniform temperature rise along the traction-free boundaries. The crack faces are supposed to be insulated thermally and electrically. By using both the Laplace transform and the Fourier transform, the thermal and electromechanical problems are reduced to singular integral equations, respectively. The singular integral equations are solved by using the Gauss-Jacobi integration formula. Numerical methods are then employed to obtain the time dependent solutions by way of a Laplace inversion technique. The dynamic stress intensity factors, temperature change and stress distributions versus time are presented for various values of deimensionless parameters representing the crack size and the material nonhomogeneity.

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Transient response of a penny-shaped crack in a plate of a functionally graded piezoelectric material (FGPM) is studied under thermal shock loading conditions. It is assumed that the thermoelectroelastic properties of the strip vary continuously along the thickness of the strip, and that the crack faces are completely insulated. Some material properties are assumed to be exponentially dependent on the distance from the crack line parallel to be boundaries of the plate. By using both the Laplace and Hankel transforms, the thermal and electromechanical problems are reduced to a singular integral equation and a system of singular integral equations. The singular integral equations are solved numerically, and a numerical method is then employed to obtain the time dependent solutions by way of a Laplace inversion technique. The intensity factors versus time are presented for various values of dimensionless parameters representing the crack size, the crack position and the material nonhomogeneity.

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Many studies have revealed that fatigue crack growth (FCG) rate of austenitic stainless steels is accelerated in light water reactor environment compared to that in air at room temperature. Major driving factors in the acceleration of FCG rate are stress ratio, temperature and stress rise time. Based on this knowledge, FCG curves have been developed considering these factors as parameters. Hewever, there are few data of FCG threshold ΔK_th in light water reactor environment. Hence it is necessary to clarify FCG rate under near-threshold condition for more accurate evaluation of fatigue crack growth behavior under cyclic stress with relatively low ΔK. In the present study, therefore, ΔK_th was determined for austenitic stainless steels in simulated PWR primary water, and FCG behavior under near-threshold condition was revealed by collecting fatigue crack propagation data. The results are summarized as follows : No propagation of fatigue crack was found in high temperature water, and there was a definite ΔK_th. Average ΔK_{eff, th} was 4.3MPa·m^0.5 at 325°C, 3.3MPa·m^0.5 at 100°C, and there was no considerable reduction compared to currently known ΔK_{eff, th} in air. Thus, it was revealed tha ambient conditions had minimal effect, on ΔK_{eff, th}, ΔK_th increases with increasing temperature and decreasing frequency. As a result of fracture surface observation, oxide-induced-crack-closure was considered to be a cause of the dependency described above. In addition, it was suggested that changes in material properties also had influence on ΔK_th, since ΔK_{eff, th} itself increased at elevated temperature.

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In this paper, the elastoplastic deformation behaviors of cylindrical tube subjected to statically axial compression are studied by using finite element method (FEM). The effects of tube geometries and strain hardening characteristics of the material on the deformation behaviors are investigated. Generally, although it is recognized that the deformation situation along the circumferential direction is dependent on the thickness ratio (R/t) , it is found that the deformation is also greatly dependent on the edge constraint. The deformation mode along the circumferential direction also affects the deformation mode along the axis-direction. A method to control the deformation mode, such as adding a disk in tube center, is proposed to maintain the deformation keeping in an axi-symmetric mode.

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In this paper, the crushing behavior of honeycomb structure subjected to axial compression is studied by using finite element method. Deformation mechanism is clarified to understand the energy absorption performance in axial compression of thin-walled tube with three-fold point corner. It is found that, in the crushing process of t-t-t model, the folds, which generate along the full length of plates, come to be crushed simultaneously. On the other hand, in the crushing process of t-t-2t model, the folds concentrate in the middle part of plates, and the deformation mode becomes the progressive one. Based on the assumption that strain energies of traveling hinges for the present and conventional models are equivalent, the conventional theoretical expression for the average load is applied to the present t-t-2t model, which ignores the occurrence of separation of glue part. Further, a theoretical prediction model for the average load of simultaneous mode is proposed. Then, the validity of the proposed model is verified comparing with the numerical results by finite element method.

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Pressurized component design codes based on design-by-analysis require the evaluation of thermal ratcheting produced by the combination of primary and cyclic secondary stresses. In the current codes for nuclear power components provide domain categorization type evaluation methods of progressive strain, using Miller's or Bree's diagram. When these methods are used with elastic analysis, the stress classification procedure with linearization of stress distribution is needed. When elastic-plastic analysis, which directly estimates accumulation trend of strains, is performed, the linearization of strain is necessary to assess the acceptability of progressive bending strain following the high temperature component design codes. These procedures for linearization can not be applied straight forwardly to general three-dimensional geometries. This paper proposes evaluation methods of Bree type ratcheting without the necessity of linearization of stresses and strains. The methods presented are based on surface strain increment or elastic core size, and are applicable to both smooth and notched components without losing the consistency with the current codes.

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This paper reports a study on crystal rotation in a single crystal copper specimen by a knife edge tool indentation. A rectangle specimen was made from a single crystal copper ingot so that its edges correspond with <100> crystal direction. Indentation tests were conducted on its {001} plane by using a knife edge tool, where the direction of tool edge were set in various direction on the {001} plane. Cross sections of the indent grooves were analyzed by FIB. Results show that indent depth depends on tool direction. Then, distribution of crystal orientation around an indent groove was analyzed by EBSD. Spin vectors of the crystal structure were calculated from EBSD data. Distribution of spin vector revealed that crystal rotation around an indent groove is separated into two zones ; the upper zone rotates to inside direction but the lower zone rotates to outside direction. Also, most of the spin vectors indicates [100] crystal orientation regardless of tool direction.

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Slurry erosion with sand particles is a serious problem for pumps operating at the Yellow River pumping station. Therefore, a technique to predict erosion volume loss is required for selecting erosion resistant material and determining specification of the maintenance period. This paper reports a method to predict the volume loss of thermal sprayed cermet layers using slurry jet apparatus. An equation for prediction is derived from combining an analysis of sand particle behavior in the slurry jet apparatus with measurement of surface profile on specimens obtained by slurry jet test by silica sand of approx. 60μm in mean diameter. There is a critical kinetic energy of particle above which erosion occurs. Critical kinetic energy of each material increase in proportion to Vickers hardness. The wear pattrem on the slurry jet test with the Yellow River sand of approx. 30μm in mean diameter can be predicted by using the above-mentioned equation.

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Cavitation erosion was studied for copper-based alloy samples (brass, high-power brass, bronze, phosphor bronze and aluminum bronze) using a vibratory apparatus in seawater and distilled water. Similar experiments for those copper-based alloy samples in seawater clarified the effects of cathodic protection on cavitation erosion. The volume loss of copper-based alloy in seawater is less than that in distilled water when the corrosion films is formed : the impact load by the bubble collapse pressure is reduced by the films' cushioning effect. Under cathodic protection, cushioning effect of the protective film of the adhesion product decreases the volume loss, as do the hydrogen gas effect and anticorrosive effect, etc. Cavitation erosion resistance of the copper-based alloy in seawater and under cathodic protection can be evaluated as well as in distilled water in macro hardness (HV). These are improved when the average hardness increases.

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In this paper, we discuss on the transient thermal stresses in functionally graded material (FGM) plates with a function of electromagnetic noise suppression, which subjected to the irradiation power and convective heat load from the surrounding medium. The FGM plates are considered as multilayered plates with the distinct homogeneous material properties in each layer. The approximate analytical solutions of electromagnetic and temperature fields in the FGM plates are then derived. The thermal stresses in the FGM plates are also analyzed using the solution developed by Sugano. Numerical calculations are carried out for epoxy resin/titanium oxide FGM plates with a graded composition expressed in the form of power function. The effects of the material composition, irradiated power, and thermal boundary condition on the electromagnetic noise suppression, temperature distribution, and thermal stress distribution are then quantitatively evaluated. In addition, the graded composition suitable for the suppression of electromagnetic noise and reduction of thermal stress are discussed.

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This paper verifies the response surfaces of artificial neural networks (NN) learned by using a method based on Bayesian inference. Mackay showed that the Bayesian method due to Gull and Skilling can be applied to regularization for NN. However, generalization ability has not been verified sufficiently for the NN response surface regularized by using the Bayesian method. If the NN response surface has good generalization ability, it can be used in the optimization process of response surface methodology (RSM) NN therefore was learned by using the Bayesian method to investigate generalization ability. We tried three rules for updating the regularizing constants in an objective function minimized during NN learning. All of the update rules were derived from the Bayesian method. As a result, the response surface of NN had good generalization ability, with the exception of one update rule. The poor update rule failed to determine the regularizing constants. This tendency for the update rules was recognized regardless of response surface geometry. After we selected a superior update rule, the NN response surface by using the Bayesian method was applied to an optimization problem. The response surface didn't fit noises included in teacher data, and consequently, it was effectively used to reach a solution. Finally, we concluded that the NN learned by using the Bayesian method can be used as the response surface in the process of RSM.

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When the human head is loaded by the translational acceleration in the traffic crash accident, the human brain is damaged at the crash side and the counter side, such as the coup and the contre-coup brain injuries. The purpose of this study is to reveal a generation mechanism of the coup and contrecoup brain injuries and develop a prediction method of the brain injury at the nerve cell level by using the dynamic-explicit finite element method (FEM). We carried out a multi-scale crash simulation by using a macroscopic head model and a microscopic nerve cell model. We have investigated the hydrostatic pressure, the equivalent stress and strains distributions in the nerve cell during the head crash against the street plate. Numerical results show the availability of our multi-scale analysis to predict the brain injury at the macro and micro levels.

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This paper introduced the finite element analyses into ergonomics designs of aluminum beverage can ends to evaluate perception of pressure applied to the human fingertip numerically and objectively. At first, experiments of indenting vertically the fingertip pulp by a probe and the tab of the can ends have been done to observe force responses and to experience feelings in the fingertip. It is found that a typical force-displacement curve can be divided into three parts according the curve gradient. We feel a touch at the first part of the force-displacement curve, and then feel pressure and our pulse at the second part, finally feel discomfort followed by pain at the last part. The finite element analyses have been performed to simulate the tab indenting the fin-gertip vertically for developing the finite element model of the fingertip. It is confirmed that the simulation results agree well with the experimental observations. Moreover, a simulation of finger lifting the tab of the can end has also been performed, and discomfort in the fingertip has been evaluated numerically to present the finger accessibility of the tab. Finally, the finger accessibility comparison of two kinds of tab ring shape designs showed that the finger accessibility of the tab that may have a larger contact area with the finger is better.

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