In large scale linite element (FE) analyses of over ten millions degrees of freedom (DOFs), it is very difficult not only to calculate but also to visualize them. This difficulty in visualization is mainly caused due to the following two reasons. Firstly, verification for large-scale analysis requires highly Interactive user interface. Secondary, it can not be handled on a conventional single processor machine any more. This paper describes a prototype of the visualization system for large scale FE solutions with millions of DOFs using a virtual reality environment named CABIN for the former issue and a PC-based cluster consisting of 24 PEs (DEC Alpha 533 MHz) for the latter issue. CABIN provides a large scale and realistic space in immersive multiscreen display. This makes it easy to understand the results, but requires excessively computer resources. Thus we employ the PC-based cluster, which supplies the processed data to the front-ended CABIN system. Practical performances of the present system are demonstrated for both three-dimensional elastic and fluid flow analyses.

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This paper describes a new method for the simulations of signals noised by the presence of other materials except for test articles in eddy current testing (ECT). In the inspection of steam generator tubes in nuclear power plants, the sensor detects structures, for example support plates to fix the tubes, and deposits adhering to their outside, as well as tube defects. The signals from the structures are thought to be noises when finding the defects. The method developed here is based on a set of governing equations constructed with magnetic vector potentials, introducing a precondition that a small part of the inverse matrix of the coefficient matrix in an algebraic equation from finite elements and the potentials for the unflawed conductor model are stored. Following the reciprocity theorem, an impedance change due to a flaw, as an eddy current signal, can be computed through integration in the flaw region, and unknowns corresponding to the flaw region only are considered. It results in much smaller degrees of freedom than typical finite element approaches require, and the method provides a fast forward simulator. The fast forward simulator is tested with experimental measurements of ECT benchmark problems with noise factors mentioned above, and is compared with a conventional approach from the point of view of computational costs.

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FEM is useful for stress analysis and used widely in general. However, it is still not necessarily easy to obtain the highly accurate values of stress intensity factors by FEM. Recently, a method for calculating the highly accurate values of mode I stress intensity factors is proposed by Nisitani, based on the usefulness of the stress values at a crack tip calculated by FEM. Although the stress value at a crack tip by FEM is finite, it is very effective as a measure of the singular stress field of the crack tip. In this study, an extension of this method to general two dimensional crack problems was made. The extended method was applied to the problems of the inclined crack, the interference of two cracks in a strip and the micro-crack in a finite plate. As the results, it was confirmed that the present method has the sufficient accuracy in all these problems.

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A new method combining the finite element method (FEM) and the molecular dynamics (MD) for silicon's complicated diamond-like structure is proposed. For simultaneous simulation, the patch model was used to exchange displacement information in both directions. A one-to-one correspondence of atoms and nodes is impossible for silicon lattice, therefore the atom was embedded in an isoparametric element. The influence of internal displacement which is the additional displacement to the continum one was taken into consideration. Martin's method was applied to calculate internal displacement and elastic constants. The conjugate gradient method was used for MD and the Newton-Raphson method was used for FEM to fine stable state efficiently, and the acceleration condition was set to raise convergence. The verification model showed that the smooth transition of displacement and stress was realized in the boundary region of FEM and MD. These value showed good agreement with elastic solution.

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Such high polymer materials as silicone gel are used for the shock absorber in sport shoes. In the stress analyses of shoe soles, it is difficult to detemine the load conditions by measured pressure. Because the distribution of pressure upon the shoe sole changes according to the stiffness of these materials, which generally show the nonlinear behavior in the stress-strain relations. So a stress analysis method considering the statically indeterminate problems is proposed to identify the pressure distributions on variable shoe sole models. The compression testing of nonlinear materials is carried out and the results of experiments indicate the effectiveness of the proposed method. And the strain energy of a shoe sole model is calculated under the condition of the identified load and compared with the result using the measured pressure directly.

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In the previous experiments of unidirectional CFRP subjected to tensile load in the fiber direction, the various fracture modes were observed, depending on the thickness ratio (t/T), the fiber volume fraction (Vf) and the testing temperature. With increasing the value of these factors, the fracture mode transferred from tensile mode to mixed mode and shear mode. On the other hand, in the analysis for fracture mode transition of CFRP by the conventional finite element method using the equivalent material constants, the results showed qualitative validity, although microscopic fracture such as the shear fracture at the interface or fiber rupture was not taken into account. In this study, the fracture propagation method is proposed for unidirectional CFRP using the homegenization method which can evaluate the micro and macroscopic response simultaneously. In the previous paper (Part. 1), the formulation of fracture propagation analysis method was introduced. In this paper, numerical analyses are conducted for the fracture mode transition of the unidirectional CFRP depending on t/T, Vf and testing temperature. The fracture mode transition can be simulated by the present analysis method and numerical analyses results agree with the experimental results.

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In the present paper, histories of transverse stresses in a carbon fiber reinforced plastic (CFRP) laminate subjected to impulsive force are analyzed theoretically by means of three-dimensional theory with anisotropic thermoviscoelastic property. The analyzed model is a simply-supported square CFRP laminate with a stacking sequence [0°/90°]_SYM undor isothermal conditions from -100°C to 200°C. The characteristics of transverse stress histories were considered from the viewpoint of themoviscoelastic behavior of CFRP. When the same force is applied to the laminate under different temperature, each component of transverse stress has the same maximum value, though its history varies slowly over the primary glass transition temperature. Therefore it is shown that elastic property of the fiber governs the maximum values of transverse stresses and histories are dependent on the thermoviscoelasticity of the matrix resin.

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A series of tensile and fatigue tests were conducted on CFRP angle ply laminate specimens with different atacking sequence, i. e. three-layered, five-layered and seven-layered laminates, which were damaged from lateral impact by a free fall rod. The extension of surface cracks and the development of delaminations were observed by using a replicating method and a scanning acoustic microscope (SAM), respectively. In all stacking sequences under fatigue loading, the crack growth process consisted of several stages, and crack growth rates gradually decreased. In three-layered specimen, a single crack was nucleated in the opposite layer to the surface which was given lateral impact. After the crack tips attained to the edge of specimen, inter laminar delamination began to extend. On the other hand, several cracks were observed in the five-layered and seven-layered specimen. In addition to the extension of cracks in the surface layer introduced by impact load, several new matrix cracks initiated at the edge of specimen. Crack growth was followed by the development of interlaminar delamination. The delamination in each stacking sequence developed along the preceding matrix cracks, and the effect of the preceding matrix cracks in the middle layer was notable in threelayered specimen. In five-layered specimen, the delaminations in the failured specimen was not influenced by the matrix cracks in the middle layer, but were affected by the cracks emanating from the free edge in the outer layer.

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Carbon fiber-reinforced carbon matrix composites (C/Cs) are usually used with anti-oxidation coating applied on their surface, The data about bonding strength between the coating and C/C substrate are indispensable for material design of C/Cs for various high temperature structures. Standardized measuring methods to evaluate the bonding strength, however, have not been established and the scratch method or the indentation method have attempted to be used. The results by these methods do not give quantitative bonding strength and are useful only for relative comparison of specimens with same geometry. In this paper, the bonding strength between SiC coating and C/C substrate with various coating conditions was attempted to be measured by specially designed shear load method. The experimental results by a this method were discussed in terms of thermal and mechanical loading conditions by using finite element analyses.

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In this study, rotating bending fatigue tests have been carried out to investigate the fatigue strength of plain and circumferentially notched specimens of Ti-6 Al 4 V alloy. The purpose of this work is to evaluate fatigue strength and notch sensitivity under various kdnds of stress concentrations. The notch radius of specimens varies from ∞ (plain specimen) to 2.5, 2.0, 1.5, 1.3, 1.0, 0.5, 0.4, 0.2, and 0.1 mm. According to the experiment results, it is found that the notch sensitivity of Ti-6Al-4V alloy for blunt notch is remarkably lower than that of sharper notch. The cause of this phenomenon is considered that slip system is limited fairly due to the crystal structure (hcp) of this kind of material. Considering to the influence of the stress gradient there is a clear difference between blunt notch and sharp notch for the surface state of tested portion. The non propagating microcracks at the specimen surface could not be observed for all notched specimens including plain specimen subjected under the stress amplitude of fatigue limit by N=10⁷ cycles.

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Rotating bending fatigue tests were carried out on specimens of ferrite-pearlitic ductile cast iron (FPDI) with a shot peening (SP) treatment. In addition, influences of the SP treatment on the fracture mechanism have been investigated, and changes in initial residual stress were discussed. As sesults, the S-N diagram showed a two-step bending behavior in long life region over 10⁷ cycles. The surface hardened layer and the compressive residual stresses were observed more than 300 μm from the surface. Furthermore, the sites of the fatigue crack initiations were transferred from the surface to subsurface over 10⁷ cycles region. Form the observations of the fracture surface before 10⁷ cycles it was clarified that the fatigue crack initiated at the surface. In this case, the compressive residual stress became smaller by cyclic loading. However, the crack initiation sites on long life regions were casting defects which exist over 300 μm from the surface. And the fatigue strength of a horizontal part at 10^e∼10⁷ cycles was dependent on surface hardness.

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Fatigue crack propagation tests had been conducted on fully pearlitic eutectoid steels with different carbon contents drawn to various strain levels. In addition, the crack growth behavior in view point of their microstructures were observed. The crack propagation resistance decreased with an increase in drawing strain at low propagation rate region and increased at high propagation rate reglon. The decrease in the threshold stress intensity factor. ΔK_th with increase in the strain was attributed to the decrease in the roughness induced crack closure level due to a decrease in the pearlite colony size. It was also shown that the size dependence of ΔK_th in the present study is different from that in the eutectoid steel, the size of which was controlled by heat-treatments. On the other hand, the decrease in the exponent m in the Paris' power law was ascribed to the increase in 0.2% proof stress through both in the decrease of the pearlite lamellar spacing and the development of high-density dislocation structures.

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In this paper an explanation was given why the crack tip temperature of recycled fiber reinforced thermo-plastics (FRTP) was higher than that of its virgin material, and the deteriorative mechanism of fatigue crack propagation property of recycled materials was investigated by measuring their crystallinity. The main results were as follows ; (1) Recycling process causes the decrease of crystallinity of fiber-reinforced PA46 because of thermal deterioration of its matrix resin. (2) It was caused by the decreasing of crystallinity in recycling process that the mechanical properties (yield strength and elastic modulus) of recycled materials were inferior to that of virgin material. The increasing of hysteretic heating for recycled materials was caused by the decreasing of mechanical properties. And the thermal conductivity of its matrix resin was reduced by the decreasing of crystallinity. Therefore the crack tip temperature of recycled materials was higher than that of virgin material. (3) Comparing with virgin material, the recycled materials have higher crack tip temperature and lower mechanical properties so that their fatigue crack propagation property was deteriorated. (4) An improvement of the crystallinity of recycled FRTP directly affects its fatigue crack propagation property.

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The influences of interaction between fatigue and creep have been studied for fiber-reinforced-PEEK (poly-ether-ether-keton) materials at elevated temperature. Especially, the mechanism of complex deterioration by heat, stress and recycling process has been analyzed. Main results were as follows : (1) The resistance of crack propagation of recycled carbon-fiber-reinforced PEEK (CF material) was equal to that of the virgin material, on the other hand, the resistance of recycled glass-fiber-reinforced PEEK was lower than that of the virgin material. (2) Strain at notch tip increased remarkebly with increasing number of cycles in fatigue process at elevated temperature. It was thought that the creep velocity was increased by decreasing of the elasticity modulus of PEEK matrix at the ultimate environmental temperature above glass transition temperature. (3) It was found that the carbon fibers were not broken by recycling process, but the glass fibers were broken by recycling process. So it was understood that the difference of resistance against fatigue crack propagation and creep due to kinds of reinforced fiber can be explained by the difference of fiber bridging effect. (4) It was suggested that the reliability of recycled plastic products would be improved by the control of meso-scopic factor.

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Surface crack growth behavior of a Si₃N₄ plate from small pre-indentations located in the contact center was investigated under ball-on-plate contact. Near surface stresses under the spherical Hertzian contact were calculated by the Hanson's analytical solution. The crack growth behavior was discussed in terms of the calculated stresses and the stress intensity factors both under rolling contact and under sliding-including rolling contact. The cracks were observed to grow only in a direction perpendicular to the motion of the ball. The maximum value of K_I, K_Imax, was found to remain constant during the crack growth. The stress intensity factor ranges, ΔK_II and ΔK_III, on the other hand, increase with the increase in crack length both under rolling contact and under sliding-including-rolling contact. All the stress intensity factors were increased by the friction force. It was found that the crack growth is controlled by K_Imax combined with ΔK_II and ΔK_III. It was also found that the crack growth is promoted by the increased K_Imax, ΔK_II and ΔK_III by the friction force under sliding-including-rolling-contact.

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This paper presents a method for evaluating stress intensity factor of interface cracks in dissimilar materials by using interaction energy release rate. Interaction energy release rate is defined based on the energy release rates of a crack of a body. corresponding to two independent loading conditions, and can be evaluated as a sensitivity of the potential energy with respect to the crack length. Since the potential energy is written by using a boundary integral in terms of the traction and the displacement over the boundary of the body, the interaction energy release rate can also be written in the form of a boundary integral for the displacement, the traction, and their sensitivity coefficients for the crack length. The boundary element sensitivity analyses are used to calculate these quantities accurately. Some numerical demonstrations show that the present method can give accurate results for the stress intensity factors of various interface cracks between dissmilar materials under coarse mesh discretizations.

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The Japanese Experiment Module (JEM), a part of the International Space Station is designed to protect its manned pressurized structure from impacts of Micrometeoroid-Orbital Debris (MM-OD) up to 1 cm in diameter. Though the probability of impacts of MM-OD with a diameter of 1 cm to 10 cm is very low, the occurrence of such large MM-OD impact will damage the JEM pressurized structure. When the damage to pressurized structures is large enough, a catastrophic failure may occur. To assess the probability of unstable structural failure caused by the MM-OD impact, we evaleated the JEM fracture mechanics parameters related to critical crack length. This report summarizes the results of JEM pressurized structure safety evaluation from the fracture mechanics aspects when MM-OD strikes.

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Symmetrical bending of a circular laminated plate containing a disc-shaped delamination subjected to uniform temperature change is analyzed on the basis of the theory of small deflection of plates. Radial inplane forces induced by bending in the parts of the plate above and below the delamination are determined by regarding the cracked part as two lapped discs hinged at both edges. For small temperature change, the plate deflects retaining mutual contact of crack faces, and in this case energy release rate is identically zero. For temperature change that is larger than some critical value, local delamination buckling occurs and the energy release rate is no longer zero. It is shown that, when the critical energy release rate concept of Griffith is adopted, the disc-shaped delamination grows unstably under constant temperature condition.

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We developed an apparatus to measure the optical birefringences in commercial LEC-grown GaAs (100) wafers by using a photoelastic modulator and a polarized laser. A He-Ne infrared laser was utilized as the light source for measurements of strain-induced birefringence in the GaAs wafers. The residual strain and stress components were calculated from the experimental results. The residual stress profiles have been evaluated to explain the correlation between the residual stress and thermal-stress-induced dislocation. From the experimental results, it is found that the residual stress evaluation of GaAs wafers will be available with our measurement.

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Ultrasonic wave velocities in a plastically deformed medium are known to depend upon its microstructural material properties. Therefore, one of the authors proposed the theoretical modeling of an ultrasonic nondestructive method to evaluate plastically deformed states. In the previous papar, it was reported that the good agreement of the experimental results with the simulated subsequent yield surfaces and the longitudinal wave velocities under combined stress states of an aluminum alloy using internal state variables of an anisotropic distortional yield model, which were determined to achieve a good fit for the experimental reults of the longitudinal and transverse wave velocity changes under uniaxial tension test, was obtained. In the present paper, the transverse wave velocities propagating an aluminum alloy in combinations of tension and torsion are numerically simulated and then compared with the experimental results to examine the accuracy of the proposed theoretical modeling of an ultrasonic nondestructive method. Moreover, the plastic anisotropy growth under combined stress states is also evaluated via the proposed ultrasonic method and results suggest that velocity changes of the longitudinal and transverse waves under plastic deformations depend on plastic stress and strain states, respectively.

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The Raman spectrum of silicon that is applied undaxial stress in several directions are observed by micro Raman spectroscopy in order to relate the measured Raman shift to the local stress present In the silicon single crystal. From polarization selection rules, we can selectively observe scattering by optical phonons in Si and determine the stress using the theory of stress effects on optical phonons. If the Raman experiments are performed in backscattering mode on {100} silicon wafers, only σ_XX+σ_YY are derived theoretically. In our measurements, the uniaxial stress was applied to the samples which were oriented three different directions. The results of calculation from measured Raman shift are good agreement with applied stress. The ability of this technique is confirmed.

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Palladium-containing braze alloys were selected because of their ductility, oxidation resistance, relatively high melting points, and lower cost than gold-based braze alloys. Newly developed palladium containing braze alloys were considered for use in brazing nickel-based alloy Inconel 600 for high temperature applications. The microstructures and joint strengths were studied in experimental brazed joints with Pd-Cu braze alloys. It is concluded that 30Pd-30Cu-40Au braze alloy is a suitable braze alloy for high temperature brazing for Inconel 600.

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The present study involves propagation of thermal and thermal stress waves in a hollow circular cylinder of Functtionally Graded Material (FGM) under laser-pulse heating. The FGM is regarded as a mixture of ceramic and metal phases, the volume fractions of which distribute continuously inside the material. The mathematical problem is one of the wave propagation in nonhomogeneous material. The formulation of the problem is based on the theory of coupled thermoelasticity along with the modified Fourier's law. A set of generalized equation is presented which governs the propagation of plane, cylindrical, and spherical waves in FGM. The solution is obtained by using the method of characteristics. Numerical results for the propagation of thermal and thermal stress waves in a PSZ (partially stabilized zirconia)/SUS304 (type 304 stainless steel) FGM hollow circular cylinder are presented in graphical form.

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This paper discusses about the characteristics of distributed genetic algorithms (DGAs). Among the several types of distributed models of GAs, this paper focuses on a stepping stone population model. The effects of the number of subpopulations, subpopulation immigration rate and immigration interval on the performance of the DGA are examined. Solving standard mathematical problems and a typical structural optimization problem, we find that there are several advantages in the stepping stone population model of DGAs : this model is very suitable for parallel computation and the optimum solutions can be obtained efficiently due to the partitioning of the population.

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The myocardial wall motion of the human left ventricles during the systole was investigated using the magnetic resonance tagging technique. Subjects were ten normal volunteers, eight patients with hypertrophic cardiomyopathy (HCM) and seven patients with hypertensive heart disease (HHD). The cardiac contractility was evaluated by the minimum principal strain in the cardiac short-axis plane, which is one of the eigenvalues of the strain tensor and which describes the maximum contraction. The results showed that the magnitudes of the minimum principal strains in local regions of the patients with HCM significantly decreased compared with those of the normal volunteers, and that the difference of the cardiac contractility between the patients with HCM and the patients with HHD was reflected on the minimum principal strains. This study may suggest that the minimum principal strain could be an alternative effective index for the quantitative evaluation of the cardiac contractility.

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