When an element is removed from a ground structure or an initial shape by genetic algorithm, homogenization method and so forth in the process for optimizing topology of a structure, its topology is probably changed. In this paper, we propose a new method of inferring the change in topology of a structure before the elimination of each element. This method can show the relation between elements of a structure and invariant factors in homology groups representing topology of the structure. As a numerical example, the proposed method is utilized for imposing topological constraint conditions on a three-dimensional structure consisting of triangular elements. The number of elements and strain energy of the structure are minimized under the conditions. As a result, it was found that a topological constraint on a zero-dimensional homology group of which rank is equal to the number of connected components of the structure is the most important one to reduce the number of elements and strain energy.

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Grain boundary (GB) structures of Al nanopolycrystalline (NPC) materials and their mechanical properties are studied by using molecular dynamics simulation. An embedded atom method (Mishin et al. 1999) is adopted to describe the interatomic interaction. First, bicrystal models are studied to evaluate the GB energies, then three different NPC models are examined to investigate the dependency of grain size, and a computational tensile test of a NPC model is carried out. In the bicrystal simulation, the result is compared with the effective medium theory, experiment and abinitio calculation and it corresponds well with them. Concerning NPC models, the atoms located in GBs are distinguished and the average site potential energy and the average specific volume over the atoms in GBs are calculated. The relation between these values and misorientation angles shows that there is a structural difference between low angle and high angle GBs and the border is about 20 degree. In the simulation of tensile test, the result shows the GB sliding is closely related to not only Schmid factor of inclination of GB plane but the GB character, i.e. it is observed at high-energy and low-density GB. Migrations of low angle GB that is not necessarily easy in coarse-grain polycrystals, are often observed. It is concluded that the mechanical properties and deformation mechanisms of NPC materials are closely related to the microscopic GB character and that the computer simulation play an important role as an indispensable tool to estimate GB character and to design the NPC materials.

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Mechanical property of materials is intensively dependent on their atomic structures. In regions with disarranged atomic structures such as grain boundaries, the property can be much different from that in the single crystal. In this study, atomic simulations of a Σ5 tilt grain boundary in aluminum are conducted to elucidate distribution of residual stress and local elastic coefficient near the grain boundary. Local stress and elastic coefficient within the range of 0.7 nm from the grain boundary differ from those in grain. The grain boundary consists of two kinds of atomic layers with different elastic coefficient, and this causes the characteristic local stresses.

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In this paper, the design method of the functional continuum by combining the fundamental simple mechanism models is proposed. First, the formula to calculate the whole displacement ratio of output to input is deduced from the mechanical analysis of the two simple functional continuum which are combined. By using this formula, the design condition amplifying displacement is obtained, and applied to the device design which amplifies the displacement into the same direction. In this design, the optimum structure, which has the maximum displacement ratio, is obtained by using the displacement ratio and stiffness coefficient that are analyzed by the finite element method of each device to this formula. As the results, it is obvious that the proposed method is useful for the design of combining the functional continuum.

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In this paper, the characteristics of the typical two models of parallel genetic algorithms; the coarse grained model and the fine grained model, are compared. Especially, the parallel efficiency on PC clusters that have no more than 10 CPUs is discussed. The cluster used in this study has two kinds of network architectures; FastEthernet and Myrinet. Through the numerical examples, these models are examined and discussed. The followings were made clarified. In the fine grained model, the master slave model, the ideal parallel efficiency is not 100%. It is concluded that the fine grained model is not suitable for this kind of cluster. On the other hand, in the coarse grained model, the population is divided into sub populations. The communication does not happen frequently. The coarse grained model is suited for this type of clusters. However, even in the coarse grained model, the data transfer schedule is needed because of the data stacking.

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In recent years, several crossover methods for Real-coded CA have been proposed. One of them, Unimodal Normal Distribution Crossover (UNDX) shows better performance than conventional methods in some benchmark tests. However, it becomes apparent that UNDX is not good in performance for ill-scaled functions. In this paper, a new crossover method. Two Parent Normal Distribution Crossover (TPNDX), which takes account of scaling is proposed and good performances are achieved for ill-scaled functions.

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In this paper, a formulation for particulate composite materials using the boundary element method (BEM) is presented. The formulation is based on the homogenization method using BEM and the analytical solutions for ellipsoidal inclusions. Green's function approaches for ellipsoidal inclusions can naturally couple with the integral equation formulations since both the methodologies are based on the same analytic solutions, namely Kelvin's solutions. Particles which are contained in particulate composite materials are thus assumed to be ellipsoidal in shape and integrals for the particles are expressed by analytical solutions for ellipsoidal inclusions. The efficiency of numerical analysis is greatly enhanced and there is no numerical error arising from integrals for the particles. Therefore, the accuracy of analysis is also enhanced. Numerical results for a unit cell model containing one particle is presented and compared with those by multi-region BEM analysis and accuracy of present BEM approach is examined. Three unit cell models containing 27, 125 and 1000 particles are then solved and the capability of present approach is demonstrated.

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A Titanium alloy composite reinforced with fiber-like TiB particles (TiB/Ti composite) has a good interface bond strength between the particle and matrix, as it is produced in-situ by a vacuum are remelting process. However, it is thought that damage, i.e. particle breakage, interface debond and so on, is more likely to occur under pre-working. In this paper, firstly an analytical model for the composite is developed to estimate effects of pre-working on elastic modulus by applying the Eshelbys equivalent inclusion method to two kinds of inhomogeneities, i.e. bonded and debonded fiber. Secondely type of damage due to a few kinds of pre-working is investigated experimentally. As a results, it is indicated that the particle breakage mainly occurs due to pre-straining in the particle orientation direction, while interface debond mainly occurs due to that in the perpendicular direction to the particle orientation. Finally good agreement between the analytical results base on the present model and the experimental ones is shown about reduction of elastic modulus with particle breakage.

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Scratching test is widely used to examine the adhesive strength of coating materials where the adhesive strength is evaluated as the critical load. However, such a critical load depends on shape of diamond indenter, frictional condition, thickness and mechanical properties of coating layer, etc. The critical load criterion cannot provide a material characteristic evaluation but a relative evaluation. This study has proposed an evaluation criterion for adhesive strength, based on the interfacial shear stress induced by the indenter. An iterative analysis method has also proposed to obtain the interfacial stress by the FEM program ABAQUS, with taking account of the tangential force. It was found that the tangential force in the scratching, which is obviously independent of the adhesive strength, has a sever effect on the critical load. The smaller the tangential coefficient is, the higher the critical load becomes. Scratch tests were carried out under three test conditions with various frictional coefficients. It was found that the experiment results can be explained based on the criterion proposed.

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The dynamic behavior of thin A 2017-T 3 aluminum circular plates of an empty vessel and a water-filled vessel subjected to spherical projectile impact was investigated experimentally. Their out-of-plate plastic deformation and crack development were observed in the velocity range from 50 m/s to 200 m/s near their ballistic limit. Also, the pressure change of water in the vessel, diameter and mass of the plug, and diameter of the perforation hole were measured. It was found that the filling of water in the vessel significantly affects the plugging process and out-of-plate plastic deformation of the plates. The diameter and mass of plugs in the case of a water-filled vessel were larger than those in the case of an empty vessel. For-water-filled vessels, the out-of-plate plastic deformation of target plates was more localized and was smaller than that of empty vessels. In addition, the out-of-plane plastic deformation of plate could be approximated by the combination of an exponential function and a linear function empirically.

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A numerical method to analyze a one-point-bend specimen with a fast propagating crack was developed using the Timoshenko beam theory. The displacement and the dynamic stress intensity factor can be obtained by this method if the time histories of the impact force and crack velocity are given. A numerical simulation of the one-point-bend impact test was carried out using the above method and the Hertz theory of contact. The time dependence of impact force (and hence the dynamic stress intensity factor) can be calculated if the impact velocity and the time history of crack velocity are given. The possibility of measuring the fast crack propagation toughness using a one-point-bend impact test machine was discussed.

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The method for measuring cyclic pressure distribution between two bodies in contact is investigated by applying the electrodeposited copper foil with pyramidal micro projections. Namely, sandwiching the foil between contact surfaces of the elements, the effects of static pressure p_m and cyclic pressure p_d on the deformation of micro projections are examined by a laser microscope. Aiming at the work hardening by p_m and cyclic softening by p_d occurred at the micro projection, the relationship among p_m, p_d and the real contact area A_r of micro projections to the elements are formulated. On the basis of this formula, the cyclic pressure distribution occurred between the circular cylinder made of carbon steel and the element with flat surface made of brass or steel compressed each other are obtained, respectively by measuring A_r by p_m and that by p_m plus p_d and the accuracy of this method is examined.

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In giant magneto-resistive (GMR) heads used for hard disk-drives, residual stress is caused by thin film processing, and thermal stress due to heat dissipation of the GMR elements. When the difference in in-plane principal stresses in the GMR elements is large, the output voltage of the GMR heads changes and thus the read/write characteristic of hard disk-drives may be deteriorated. We have analyzed the stress in a GMR head by a finite element method with three-step zooming models. Then, we calculated the effect of this stress on magnetic performance of the GMR head. It was found that an intrinsic stress in the protective layer must be optimized and temperature increase of a GMR element must be decreased during operation to decrease the effect of the stress on magnetic performance.

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In this paper, a singular integral equation method is applied to calculate the stress intensity factor along crack front of a 3D rectangular crack in an infinite body under mixed mode loading. The body force method is used to formulate the problem as a system of singular integral equations with singularities of the form r^-3 using the stress field induced by a force doublet in an infinite body as fundamental solution. In the numerical calculation, unknown body force densities are approximated by using fundamental density functions and polynomials. The present method yields rapidly converging numerical results for various aspect ratios of a rectangular crack. Distributions of stress intensity factors are indicated in tables and figures with varying the shape and Poisson's ratio. The maximum stress intensity factors K_IImax and K_IIImax are found to be controlled by the √area parameter in a similar way of the case of K_Imax.

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In this paper, the plastic stress intensity factor for a crack lying on a bimaterial interface is studied by using the finite element method. In the analysis, it is assumed that both materials obey Ramberg-Osgood stress-strain formulation, and have different Young's modulus E and different strain hardening exponent n. Detailed results under plane stress condition are investigated. When both materials have different values of E, oscillatory singular stress field develops near the crack tip, and decreases with increasing the plastic zone. When n₁≠n₂, variations of stress δ_y and τ_xy, on the interface are independent of lower value n of (n₁, n₂), and are functions of higher value n of (n_i, n₂). In addition, the variations of √δ²_y+τ²_xy, has stress singularity form as -1/(n+1) for higher value n of (n₁, n₂). Moreover, the plastic stress intensity factor K_p for n₁≠n₂ is almost the same value of that for n₁=n₂=n with higher value n of (n₁, n₂).

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The experimental relationship between the strain range at a notch root and the number of cycles to the strain at a notch root of X% before the initiation of microscopic surface cracks in the low cycle fatigue region has been shown as the fatigue life rule. This relationship is based on the characteristic of the cyclic strain behavior at a notch root obtained by the fatigue test of a specimen with notches under the bending deflection control. Strains are measured by strain gages. From the test data, some cyclic strain behaviors at a notch root such as the cyclic maximum strain, the strain range and the mean strain are shown. The cyclic change of the strain distribution near notch roots is also shown. Some special characteristics are mentioned.

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Since linear fracture mechanics was proposed by Irwin in 1957, its usefulness has been recognized widely. However, there is no detailed discussion about the range of applicability of linear fracture mechanics (Linear Crack Mechanics). Originally, linear fracture mechanics should be called linear crack mechanics. Recently, non-linear crack mechanics was proposed by one of the authors and its usefulness was confirmed though the analysis on the limited numbers of geometrical conditions. Considering these facts, first the effectiveness of non-linear crack mechanics is confirmed by FEM analysis on a wide range of geometrical conditions. Then, the effective range of linear fracture mechanics is discussed based on non-linear crack mechanics, taking as examples the cases of a strip with a center crack and a strip with two edge cracks under tension.

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At a tee junction point of piping system or labyrinth structure of pump seal, hot and cold water are mixed with each other in whirl. The vibrating mixing boundary between the hot and cold water induces a temperature fluctuation on a inside surface of the pipe just after the connection point or labyrinth land and bottom surface. The temperature fluctuation causes thermal fatigue. In this study the thermal stress distributions in the labyrinth structure were analyzed using FEM for various frequencies under the temperature fluctuation of turbulent water flow. The fracture mechanics analysis indicated that the thermal fatigue crack with relatively high frequency of 0.1 Hz to 25Hz were arrested at a depth nearly proportional to square root of reciprocal of the frequency and it was about 3.8 mm for 1Hz.

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In order to clarify the effect of strength level on the fatigue property in a wide life region, fatigue tests in the life region of N=0.5∼10⁹ were performed for high strength steels of SUJ 2, SNCM 439 and the carbon steel of S 35 C with low strength. S-N characteristics of respective steels were compared with each other and the fatigue mechanisms were discussed from a view point of fractography. Thus, it was found that the S-N curve for SUJ 2 steel in the medium life region can be straightforwardly connected to the static strength level, but the S-N curves for SNCM 439 and S 35 C steels in the low cycle region tends to be horizontal so that the S-N curves have the reversed S-shape. It was also found that S-N property for high strength steels of SUJ 2 and SNCM 439 were explained as duplex S-N characteristics corresponding to the surface induced fracture and interior inclusion induced fracture with a fish-eye, respectively. However, the S-N property for the low strength steel of S 35 C does not have such an aspect, but it has the simple S-N characteristics corresponding to the surface induced fracture. Consequently, the duplex S-N property of metallic materials in the ultra-wide life region appears depending on the strength level.

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In the previous report, creep damage evaluation method was studied for creep and creep-fatigue situations of Cr-Mo-V rotor steel and the stress-strain equations were devised by trial and error to simulate the creep and creep-fatigue behavior. However, to simulate the experimentally obtained behavior of the grain-boundary cavity, further improvement must be applied to the equations. In this report, it is assumed that grain-boundary sliding is not only caused by creep strain but the effect of plastic strain must be considered, and inelastic strain is composed of 5 components i.e. ε_bpl, ε_bcr, ε_pl, ε_cr, and ε_dp, where ε_bpl and ε_bcr are the strains due to grain-boundary sliding, ε_pl, ε_cr and ε_dp are the strains due to the deformation of grains. Considering the inequality of each strain component and the inner stresses due to inharmonious values of components, new improved stress-strain equations were devised. The result of simulation shows good agreement with the result of experiment in creep deformation, creep-fatigue deformation, creep rupture behavior and cavity behavior on the grain-boundary, but the agreement with the number of cycles to failure and stress relaxation behavior in the strain-cycling tests with hold time is not enough. This may suggest that the decrease of the number of cycles to failure is caused by inelastic strain with surface oxidation etc. during the hold time rather than the accumulation of grain-boundary sliding.

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In order to understand warping of crack extension in a thermal stress cleaving near a free edge of a rectangular plate, unsteady thermal stress field was analyzed on a rectangular region with an extending edge crack and a moving heat. The thermal stress field in an infinite region corresponding to the temperature is similar to the one due to a line heat. Hence the thermal stress intensity factor of an edge crack whose tip locates in a middle region is expected not to depend strongly on the crack length. Using stress intensity factors, K_I and K_II estimated by FEM, their distribution maps against the heating position have been constructed. The crack warping toward the free edge is explained from the sign of K_II in the case of heating on a crack extending line. Null K_II is achieved by heating a little above the crack extending line and straight crack extension may occur by heating there. The region giving negative K_I and positive K_II by heating is effectively utilized to give positive K_I and negative K_II, by cooling and hence cooling reduces the warping tendency. It was concluded that for the thermal stress cleaving, the effective region to be heated or to be cooled exists around the crack tip.

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