In recent years, more large-scale and complicated numerical analysis came to be performed in connection with fast development of technology. Such a large-scale problem is carrying out parallel computing, and has realized a short time and highly precise analysis. However, since the knowledge of parallel computing and experience are needed for development of a parallel analysis program, for a common user, it becomes the work which spends a remarkable labor and time. Then, in this study, the parallel FEM analysis code was developed using the plug-in function of GeoFEM. The plug-in function here is for developing parallel FEM analysis code without the knowledge of parallel computing. And parallel performance evaluation of the developed program was performed, and it checked that the high parallel performance of 80% or more of the rates of CPU usage came out also under a low communication performance like PC cluster.

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This paper describes a very fast and robust parallel solver for large scale finite element analyses. This algorithm is newly invented as an extension of the parallel CG (Conjugate Gradient) algorithm combined with the domain-decomposition-based CPG (Conjugate Projected Gradient) algorithm. Here a coarse space is defined as the space spanned by an appropriately arranged motion of subdomains, while a fine space is defined as the K-orthogonal complement space of the coarse space, where K is a stiffness matrix. The CPG algorithm with the K-orthogonal projection to the fine space is employed in the space of total degrees of freedom (DOF) of the whole analysis domain. Thus we named this algorithm CGCG (Coarse Grid based CG) method. To demonstrate its practical performance, the algorithm is applied to solve the following two problems : (a) an aluminum wheel of automobile with about 4.8 million DOF mesh, and (b) a long cantilever beam with an aspect ratio of 4 000 subjected to a bending force. For the purpose of comparison, both problems are solved by the following two different parallel solvers : (i) the domain decomposition method (DDM) and (ii) an ordinary parallel CG algorithm. It is clearly shown from the former analysis result that the CGCG solver is superior to the other parallel solvers in terms of computation speed. It is also shown from the latter analysis result that the CGCG solver is far more robust than the other parallel solvers in terms of the number of iterations.

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In this paper, location, angle and size of plural defects in a structural component are identified by an elastodynamic boundary element method. Each defect is noncircular and represented by 5 parameters, a radius, an angle, x and y coordinates of the location and the degree of distortion of its shape. External force of harmonic excitation is applied to the component and the displacements at points on its boundary are chosen as additional information. The square sum of the differences in displacements between real values and inference from numerical solutions is minimized to identify the defects using the conjugate gradient method. Though the number of defects is assumed to be one in the beginning of the identification process, the assumed defect is divided into two parts when the value of the parameter representing its distortion satisfies a certain condition. To judge correctly whether it should be divided, it is assumed that defects are filled with imaginary material of which mass density and Young's modulus are considerably low in comparison with those of a structural component.

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Molecular dynamics simulations have been performed for the Ar bombardment to Si surface in order to investigate the damage and etching properties. The dependence of the ion energy, the polar angle of the ion and substrate strain was investigated. The averaged number of interstitials was found to be a linear function of the damage energy, and its slope showed good agreement with the Kinchin-Pease model. The averaged number of etched atoms was not linear and its efficiency decreased as the ion energy was increased. It was found that the damages and etchings were caused by the energy injection to the substrate inside and the instantaneous thermal spike of the substrate surface, respectively. Mixing of two types of collision, i.e. binary and many body collisions resulted in increased dispersion of the damage. The damage decreased as the polar angle was increased. Conversely the etching increased, and had the maximum value at 70 degree. The strain dependence showed the symmetrical increased curve both in tension and compression. However, under 10% compressive strain and 1000 eV ion energy, the blocking and instability of the lattice created the significant disorder region.

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Woven fabric composites have superior ductility, tear strength and impact resistance to the conventional unidirectional fiber reinforced composites. However, it is very difficult to reveal their mechanical behaviours due to the geometric complexity. Especially, the damage, several kinds of failure such as matrix cracking, fiber breaking and transverse cracking in fiber bundle, affects and complicates the mechanical behaviour. In order to analyze the mechanical behaviour of plain woven fabric composite plates, the three-dimensional finite element analytical code based on damage mechanics, which has been developed in the previous paper, has been improved. In this paper, the priodic boundary condition has been applied and the mechanical behaviour under tensile load has been analyzed to catch the material properties without the effect of free edge. On the other hand, uniaxial tensile test has been performed and the damage development at the center area of specimen has been observed by CCD camera. As the results, it is recognized that the calculational and the experimental results have a good agreement and that the proposed procedure is very useful for the material design of woven fabric composites.

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Nanoidentation for three ferrite-pearlite steels, S25C, S35C and S45C, was conducted in order to examine tensile strength versus microstructural parameters and fatigue limit versus microstructural parameters. Nanoindentation on ferrite showed that converted Vickers hardness was kept constant independently of steels and indentation sizes, and almost equal to the base hardness of iron of 100. Nanoindentation on pearlite showed that converted Vickers hardness increased with indentation size and saturated at about 250. The saturated value was estimated as the inherent hardness of pearlite. Two equations of tensile strength versus microstructural parameters proposed by Pickering and others were consistent with nanoindentation results. Similar equation was obtained from nanoin-dentation result for each steels, using the law of mixtures. The equation of fatigue limit versus microstructural parameters proposed by Grozier and others was necessary to be modified on the basis of nanoindentation results. It was found from these results that nanoindentation was useful for the strength analysis of ferrite-pearlite steels in a nanoscopic scale.

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A multi-scale computational method using the homogenization method is applied to the stress analysis of ceramics considering the random and complex microstructure three-dimensionally. The main purpose of this paper is to propose a numerical method to understand quantitatively the microscopic stress distribution in the random microstructure especially for porous ceramics. The voxel mesh is used to model the microstructure automatically with the help of the image-based modeling technique. In the analysis of porous alumina with needle-like random pores, the distance from the nearest pore is measured for all the voxel elements, which is plotted with the histogram of the microscopic stress distribution. This is of great help to study the relation between the stress concentration and the pore geometry and dispersion.

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Fatigue behavior characteristics of hybrid composites with non-woven carbon tissue are inves-tigated under tension-tension fatigue loadings. Hybrid laminates are made by interleaving non-woven carbon tissue between CFRP-prepreg layers. Ten kinds of laminates are studied; namely, non-woven carbon tissue laminates, transverse [90]₁2, off-axis [45]₁2 and angle-ply [±45]₃S CFRP laminates, and transverse ([90//90//90//90//90//90/]_S, [//90//90//90//90//90/]_S), off-axis ([45//45//45//45//45//45/]_S, [//45//45//45//45//45//45/]_S) and angle-ply ([+45//-45// +45//-45// +45//-45]_S, [//+45//-45//+45//-45//+45//-45]_S) hybrid laminates. The symbol "//" means that the non-woven carbon tissue layer is located between the CFRP-prepreg layers, and the symbol "/" means a half of non-woven carbon tissue layer thickness. The effects of non-woven carbon tissue on the tension-tension fatigue life of all hybrid specimens, and moreover the residual strength and stiffness of angle-ply hybrid specimens are evaluated. The fatigue damage and failure mechanisms of the hybrid composites are discussed through observation results with an optical microscope. The hybrid composite laminates seem to be effective to improve the fatigue characteristics.

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S_i3N₄/SiC composite ceramics were sintered and subjected to three-point bending. A semi-elliptical surface crack of 100μpm in surface length was made on each specimen. A crack was healed under static bending stress of 210 MP_a at 800, 900 and 1000°C. Applied stress of 210 MP_a is ∼70% of the bending strength of as-cracked specimen. Bending strength and static fatigue strengths of crack-healed specimens were systematically investigated at each crack-healed temperature. The bending strength of crack healed specimen showed almost the same value as the smooth specimen. Thus, Si₃N₄/SiC composite ceramics could heal a crack even under static bending stress of 210 MP_a at 800, 900 and 1000°C. Moreover, crack-healed zone had sufficient static fatigue strength at each crack-healed temperature. These conclusions indicate that Si₃N₄/SiC composite ceramics has the ability to heal a crack under service condition, i.e. high temperature and applied stress.

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Many of the ceramic coating materials can be exposed to harsh working conditions. Therefore, for producing superior coating materials, it is necessary to establish a methodology for evaluating the mechanical properties of these materials. Until the former report, nine kinds of TiN film 5 μm thick, which were deposited on the different parent materials under different N₂ partial pressure, were scratched and the relationship between the characteristics of the detected acoustic emission (AE) signals and the fracture modes of the film (i.e. cracking, chipping and flaking) was investigated. As the results, the following things became clear: (1) the fracture modes were classified by fractal dimension m determined AE peak amplitude distributions. (2) the changes of the fracture mode were evaluated by observing the analysis with wavelet transform (WT). In this report, time fluctuation signals of wavelet coefficient, multiple analysis and fuzzy reasoning were used to evaluate the scratch mark conditions. From the experimental results, it was found that the conditions were evaluated by this method.

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The plastic strain range of stress-strain curve during fatigue process was measured for an annealed and a rolled steel for general structure SS400. It was found that variation in plastic strain range Δερ was expressed using movable dislocation density ρ and Burgers vector b. The movable dislocation density was estimated from the plastic strain range and was expressed as a function of the number of stress cycles n by the following equations using a model based on the multiplication and annihilation process of dislocations. Δε_ρ= √ρb, ρ= 1/(β/α+ 1/ρ₀e-^an+βk/αn). It was concluded that the calculation using this equation corresponds well with plastic strain range.

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Crack initiation and crack growth behavior were studied on a ferritic stainless steel, SUS444, as a function of specimen orientation. Fatigue tests were conducted in laboratory air and in 3%NaCl solution using electro-hydraulic fatigue testing machine. Specimens with two different orientations, i.e. L and T direction, were prepared. In both orientations, cracks initiated from slip bands within ferritic grains. The effect of specimen orientation on fatigue lives was not observed in both environments. However environmental effect was found on fatigue lives, i.e. fatigue lives were shorter in 3%NaCl solution. In early crack growth region, while no discernible differences were found between both directions, crack growth rates in 3%NaCl solution were faster than in laboratory air. In long crack growth behavior, the anisotropy was only observed at low ΔK region, where the crack growth rates in specimens with L-T orientation were faster than those with T-L orientation. Taking account of crack closure, the crack growth in both orientations exhibited a similar behavior. Environmental effect was also found in the region of ΔK≥15 MPa √m for both orientations, where crack growth was enhanced in 3%NaCl solution.

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Plane bending fatigue tests were carried out for sand cast magnesium alloy AZ 92 A-T 6 in air at room temperature, in order to investigate fatigue crack initiation behavior and notch sensitivity. Successive observations on the surface have shown that the fatigue crack initiates along the slip bands in an α grain and starts to grow into the neighboring grain or lamellar precipitate phase. The notch sensitivity was higher than that in pure titanium that has hcp crystal structure. However, no non-propagating crack exists for a sharp notch (ρ=0.1 mm). Fractography using SEM has shown that the crack in which the micro pores in the vicinity of the surface became an origin, propagated and often led to final failure in the region of life N_f≥5× 10⁵. In this case, the initial stress intensity factor; ΔK_I ini was from 0.52 to 0.73 MPa ·√m, when the micro pore was considered to be a crack.

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Anti-erosion performance is one of the design requirements for helicopter rotor blades. To satisfy this requirement, a metal abrasion strip is bonded on the leading edge of composite rotor blades. The stainless steel abrasion strip is subjected to very high-cycle fatigue with high strain ratios due to large flexibility of rotor blades made of glass fiber reinforced plastics (GFRP). This study selected AISI 301 1/4-hard austenitic stainless steel 0.8 mm thick as a material for abrasion strip. High cycle fatigue properties of this material were investigated under tension-tension cyclic loading with stress-control. The results revealed the fatigue process of the specimen in detail based on the material response between true stress and true strain. A fatigue design curve for the abrasion strip was proposed and the advantage of hardened materials was clarified.

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In order to investigate the criterion for the nucleation of persistent slip bands (PSBs) near a ∑3(111) coherent twin boundary, where is a preferential site for formation of PSBs, a high-cycle fatigue test is carried out at room temperature using a copper bicrystal specimen with the twin boundary. PSBs are observed near the boundary in the connection with the evolution of extrusion! intrusion on the specimen surface. The slip behavior is different from that predicted by the Schmid factor. A finite element method (FEM) analysis is conducted for the bicrystal, and it reveals that the increase of resolved shear stress on the specific slip system due to the constraint of deformation between the crystals is the main cause for promoting the nucleation of PSBs near the twin boundary. By taking into account the interaction between the primary and the secondary slip systems, it is possible to specify the nucleation behavior of PSBs near the twin boundary.

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Stress intensity factor (K value) is often used for evaluating the reliability of cracked structure. In this study, the K value of interacting parallel surface crack is calculated using the finite element method. A simplified mesh generation method is adopted in order to improve the complexity of mesh generating procedure. The influence of interaction between cracks on the magnitude of K is discussed based on the results under various conditions of relative location, aspect ratio and crack depth/ thickness ratio. For example, if the inner crack tips cross each other, K value is enhanced at the deepest point rather than the one near the surface. When cracks are close enough, the stress distribution is almost the same as that of a coalesced crack. Since the aspect ratio of a coalesced crack is smaller than that of the separated cracks, K value near the closest crack fronts is enhanced.

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The stresses of a pipe flange connection with a spiral wound gasket under internal pressure are analyzed taking account a non-linearity and a hysteresis of the gasket by using axisymmetric theory of elasticity and finite element method (FEM). The leakage tests were also conducted using the actual pipe flange connections with spiral wound gaskets. Using the contact stress distribution of the pipe flange connections with 3" nominal diameter under internal pressure, the values of the new gasket constants proposed by PVRG are estimated by taking account the changes in the contact stress. A difference in the new gasket constants is substantial between the PVRC values and the estimated results, which are obtained by using the initial clamping stress. However, the difference is small between the PVRC values and the estimated values which are obtained by using the actual gasket stress. In addition, a method for determining the bolt preload for a given tightness parameter is demonstrated. The obtained results for the pipe flange connection are in a fairy good agreement with those obtained by PVRG procedure.

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In order to make clear the crystallographic interpretation of each factor composing the Hall-Petch relational equation, experiments were performed by using two kinds of polycrystalline pure aluminum, which were annealed at 573 K and followed by quenching from 773 K. The In-Situ observations of the appearance or morphological change of slip bands were continuously carried out in the surface grains from elastic strain range to yielding. The main results obtained indicate that the Hall-Petch rule is proper for slip deformation in a polycrystalline aluminum which consists of the heterogeneous grain sizes. The Hall-Petch slope decreases with increasing of the number of active slip planes in the slipped surface grains just after yielding. Moreover, the friction stress after yielding shows a lower value than the yield stress of the single crystal, but the quench-harding increment in a polycrystalline aluminum is consistent with that of the single crystal.

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7475 type Al-Zn-Mg-Cu alloy polycrystals which consist of the average grain sizes ranging from 27 to 283 μm were prepared by solution treating at 753 K and aging at 393 K for various times. Tensile tests and micro hardness tests for these specimens were performed to evaluate both the Hall-Petch relation and three kinds of strengthening mechanisms. Correlation between the flow stress or Vickers hardness and the inverse square root of the average grain size are all represented by straight lines. The Hall-Petch slopes are nearly independent of the strain quantities and aging times, but the friction stresses increase with those increments. The contributions of grain refining effect, solid solution and precipitation strengthening to the 0.2% proof stress of the aged specimens for 86.4 ks are estimated to be 5, 82 and 310 MPa, respectively. Moreover, the rate-controlling mechanisms of yield behavior in the precipitation strengthening are made clear by comparing the experimental values with the theoretical ones.

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Gas turbine operating conditions are severe, especially for hot-gas-path components. The components are subjected to the conditions of thermal load, dynamic pressure oscillation, and environmental attack due to hot gas. However, the service conditions are complex and difficult to determine. To improve the accuracy of the life assessment of such components, an analytical method for estimating the service boundary conditions for these components has been developed. This method consists of FEA (finite element analysis), design of experiments, and metallurgical inspection of actual machine components. The FEA_s varied with boundary conditions are analyzed using an orthogonal array. In each analysis, difference between results of an FEA and results of the metallurgical inspection are estimated. The model is modified to reduce the difference by using analyses of variance. The modified model is applied to damage analyses and life assessment. The method was applied to a gas turbine blade and the good agreement between the analysis results and the inspection data confirmed the validity of the method.

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