A series of creep-fatigue tests were carried out using 316 FR steel at 650°C in a very high vacuum environment of 0.1 μPa under loading conditions of sequential changes from creep-fatigue loading to fatigue loading and vice versa in order to examine the accumulation behavior of creep, fatigue and creep-fatigue damages with respect to a strain cycle. The linear summation of life fraction is smaller than unity in the case of creep-fatigue loading followed by subsequent creep-fatigue loading. However, the deviation from unity is not very large for this material. A sequential change between slow-fast creepfatigue loading and fatigue loading gives a summation of life ratios less than unity. On the other hand in the case of a tensile strain hold-time cycle, the summation of life ratios exceeds unity. Other tests have been conducted to simulate creep-fatigue behavior when the material is subjected to a safe shutdown earthquake (SSE). In this case the creep-fatigue life reduction is not very large.

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In order to investigate the basic fretting fatigue properties of two kinds of near-α titanium alloy, fretting fatigue tests were carried out under axial loading conditions using a bridge-type contact plece. The influence of contact pressure on fretting fatigue properties was also investigated. The main results obtained are as follows. In both materials, fretting reduced the fatigue lives by a factor of four as a result of the initiation of the fatigue crack at early stage of life and acceleration of the crack propagation rate. Fretting fatigue lives decreased with increasing contact pressure. The difference in fretting fatigue lives among the materials used is explained by different of tangential force coefficients and fatigue crack growth properties, as well as compressive residual stress introduced by shot peening.

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The influence of dual phase on the fatigue reliability of the intermetallic compound TiAl alloy at an elevated temperature was examined through in-situ observation of mesocrack behavior with scanning electron microscope (SEM)-servo testing. The main results obtained were as follows : (1) The fatigua strength ratio, that is strength/density, of intermetallic compound TiAl alloy at 1073K under vacuum is excellent. (2) During most of the fatigue life of the intermetallic compound TiAl alloy, mesocrack growth was observed. Thus, the fine fatigue property of TiAl alloy is due to its higher resistance to mesocrack growth. (3) The effect of dual phase on fatigue crack growth was considerable. In the early stage of fatigue life, plastic deformation was observed in the lamellae structure, it triggered the γ phase brittle cracking. After that, brittle cracks in the γ phase caused shear cracking in the lamellae structure at the medium stage of fatigue life. Many mesocracks that is brittle crack in γ phase and shear cracks in lamellae structure, coalesced with each other into one inacro fatigue crack.

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The effect of "Inter-Heat"treatment, that is composed with different two types of "bainitic heat treatment"and"micropulse induction heating", on the fatigue reliability of spherical graphite iron was studied. The main results obtained were as follows, (1) A martensite structure of higher hardness on the surface layer and A bainite structure of higher toughness in the interior of SGI specimens were produced by "Inter-Heat"treatment. (2) The fatigue strength of "Inter-Heat"treated SGI was intermediate between the fatigue strength of martensitic SGI and bainitic SGI. (3) Fatigue cracks initiated at the micro-porosity in the internal bainite structure. The fatigue crack propagation was controlled by means of the residual stress induced by"micropulse induction heating".

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This paper describes the effects of shot peening and artificial small defects on the fatigue strength of austempered ductile cast iron (ADI). The fatigue strength of smooth specimens was increased by shot peening in a short life regime and the increments reached about 33 and 29% at 10⁵ and 10⁶ cycles, respectively. The improvement of fatigue strength, however, almost disappeared in a long life regime of 10⁸ cycles. Small drilling holes were used as artificial defects. The diameters of the holes were 0.1, 0.2, 0.3 and 0.4mm and their depths were almost the same as the diameter. The fatigue strength of the specimens with a 0.1mm drilling hole did not decrease when compared with that of the smooth specimens, but the fatigue strengths of the specimens with 0.2∼0.4mm drilling holes decreased. The experimental results of the specimens with 0.2∼0.4mm drilling holes were consistent with the predlction by Murakami's √(area) parameter model. The maximum size, (√(area))_max, of the pre-existent defects in ADI was equivalent to the defect of the specimen with a 0.1mm drilling hole and was estimated to be about 90 μm by the above model.

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Fatigue crack growth tests using center-cracked specimens [M (T) specimens] of SUS304 steel were conducted to examine the behavior of fatigue crack growth in the near-threshold regime at 450, 550, 650, and 700°C. Using the interferometric strain/displacement gage (I.S.D.G.), the crack closure behavior, which was thought to be significant due to oxide film accumulated on crack surfaces, was examined. It was shown that the crack closure level was measured with good accuracy even at high temperatures by I.S.D.G. modified using a platinum plate and a filter. It was found from the behavior observed at 650°C that crack closure did not occur at R=0.5, and that changes in the behavior of crack growth rate, da/dN, corresponded to those in the behavior of crack opening ratio, U, at each test temperature.

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Fatigue crack growth tests were conducted at 450, 550, 650 and 700°C. Crack closure level was measured using the interferometric strain/displacement gage (I.S.D.G.), described in the previous paper, Crack growth rates for stress ratio R=-0.1 plotted against stress intensity factor range, ΔK, deviated from those for R=0.5. Using the effective stress intensity factor range, ΔK_eff, which was calculated using crack opening ratio determined from the I.S.D.G. measurement, the R-dependence of the crack growth behaviors for R=-0.1 and R=0.5 were reconciled at each test temperature. A threshold value, ΔK_{eff, th,} of fatigue crack growth was determined at each temperature. It was found that the threshold value reached a maximum at a temperature between 450 and 550°C.

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In order to investigate the influences of grain size, and PSZ and SiC whisker reinforcements on cyclic fatigue crack growth characteristics for alumina ceramics, cyclic fatigue crack growth tests were carried out on both sintered alumina ceramics with various grain sizes and alumina matrix composites. It is shown that there is a large influence of grain size on fatigue crack propagation behavior, and that the crack growth rate da/dN of coarse-grained alumina ceramics is lower than that of fine-grained alumina ceramics. It is also found that PSZ and SiC whisker reinforcements are effective in improving fatigue crack growth resistance of alumina ceramics.

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The initiation of microcracking is a trigger for macrocrack initiation of fretting fatigue. The initiation behavior of microcracking is governed by the contact pressure and the relative slip. A new measuring system was developed to measure the relative slip at a local point of contact in a fretting fatigue experiment using a laser displacement meter. It was found that the simultaneous operation of irreversible slip range above 2 μm and contact pressure above threshold value was necessary for microcrack initiation of fretting fatigue.

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To investigate the effect of atmospheric humidity on cyclic fatigue crack growth behavior, fourpoint bending fatigue tests were performed on silicon nitride in laboratory air and toluene. Crack aspact ratios for surface cracks in laboratory air were clarified to be lower than in toluene, The relationship between crack growth rate and maximum stress intensity factor for small surface cracks was obtained using the above crack aspect ratios. This result indicated that crack growth rate was accelerated by atmospheric humidity in the low stress intensity factor range, but not in the high range. This acceleration was clarified to be causes by the mutual action of cyclic stressing and atmospheric humidity. Microcrack initiation ahead of the main crack, the cutting process of ligament between the micro and the main crack, and cyclic loosening of crack bridging at wake of the crack tip were ciarified to be dominant factors which influence the crack growth behavior in both environments.

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In this study, an improved quench-type testing method for thermal shock experiments was developed. Repeated thermal shock tests were performed on cemented carbides to illustrate the advantages of the new method, which enabled us to esimate the intrinsic cyclic fatigue crack propagation behavior during repeated thermal shock tests and thermal fracture toughness values. It was shown that cyclic thermal fatigue crack propagation behavior and fracture toughness values were independent of the specimen height and cooling media of two different viscosities employed.

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An investigation of water absorption effects on the impact fracture mechanism and compression after impact (CAI) behavior was conducted using carbon fiber reinforced thermoplastic matrix composite (AS-4/PEEK) and aramid fiber reinforced epoxy matrix composite (K-49/828), which have a quasi-isotropic stacking sequence of [0°/±45°/90°]_2s. The impact tests were carried out using a falling weight tester. Impact-induced internal damage was observed with a scanning acoustic microecope (SAM). The delamination area was evaluated by the subtraction method. The delamination area of AS-4/PEEK was much smaller than that of a CF/epoxy composite (MM-1/982X), and no influence of water absorption was observed. In contrast, that of K-49/828 was the largest, and the impact-load-induced delamination area was increased by water absorption. In the case of AS-4/PEEK the compressive strength of the impacted specimen at 3 J was the same as that of a virgin specimen, and no influence of water absorption was observed. Impact energy affected the CAI strength of K-49/828 as much as that of MM-1/982 X. The fracture surface was closely examined using a scanning electron microscope, and the fracture mechanisms were discussed.

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A simole equation to approximately calculate the stress intensity factor of the circumferential crack of cylinders under axisymmetric bending was derived first. By applying it, and equation to evaluate the stress intensity factor for the same crack under thermal stress distribution with practically sufficient accuracy was deduced theoretically. The latter equation is valid for arbitrary axisymmetric temperature distribution, which has its gradient in the radial direction. The effect of the length of the cylinder on the stress intensity factor can be evaluated by using the equation. Investigation of the characteristics of the stress intensity factor of cylinders under radial temperature distribution was conducted, by using the equation. It was shown that the stress intensity factor is in proportion to the'equivalent moment, 'which is calculated from the temperature distribution. In addition, for cylinders with practical dimensions such as R_m/W<20 (R_m : mean radius, W : thickness), the stress intensity factor showed a peak value with the increase of the crack length. The reason the stress intensity factor shows a peak value, was concluded to be because of the fundamental characteristics of the structure of the cylinder, which produces reaction force to close the crack.

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The "A"parameter method is frequently used to estimate creep damage of Cr-Mo-V steel forged rotors. The creep damage value estimated by this method may vary owing to the variance of data and the different means arising from different etching methods and/or the discrimination of different examiners. In this study, the variances and the means were calculated from numerous"A"parameter data of the same creep-damaged Cr-Mo-V steel forgings. Comparing these data with data from previous studles, the following results were obtained : (a) A method for estimating creep damage value which guaranteed an optional degree of safety was determined. (b) It was suggested that the percolation of grain boundaries played a large part in creep rupture of Cr-Mo-V steel forged rotors.

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In recent years, to enhance the interlaminar fracture toughness of CFRP laminates, interlaminar toughened laminates have been developed with resin-rich layers in the interlaminar regions. In the present study, stress and displacement fields in interlaminar-toughened cross-ply laminates with transverse cracks are analyzed. The analysis is based on a two-dimensional model which assumes that generalized plane strain conditions prevail. Thermal residual stresses arising from a mismatch in thermal expansion coefficients of the 0°, interlaminar resin and 90°plies are considered. The analytical results are shown for the laminates with interlaminar resin layers of various thicknesses. The analysis will provide a basis for the optimal design of laminates with interlaminar resin layers.

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In order to clarify the mechanism of the creation of compressive residual stress by shot peening, a static compression test and a dynamic impact test using a single steel ball against a flat steel plate were carried out. In the static compression test, compression residual stress was created near the center of the ball indentation mark. However, in the dynamic impact test, tensile residual stress was created near the center of the ball indentation mark and compression mark and compression residual stress was created outside of the indentation. Furthermore, the tensile residual stress in the center of the first ball indentation mark changed to compressive stress as the density of the ball indentations surrounding the first ball indentation mark increased. Therefore, the compressive residual stress created by shot peening is considered to be the result of the superposition of residual stress produced by surrounding shots.

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This paper discusses the problem of stresses of two joined materials, [I] and [II]. Material [I] is a large plate with an elliptic hole and [II] is an elliptic patch plate. There are two different conditions. One is the difference in the mechanical properties, the other is the difference in the initial elliptic boundary dimensions. Before joining, some amounts of dislocation exist on the elliptic boundaries between [I] and [II]. For continuous connection of both boundaries, we analyzed the necessary boundary tractions, q_x and q_y, theoretically using Goursat's stress functions and Dundurs' parameters. As a result, we obtained generally applicable formulae for expressing q_x and q_y and reported the fundamental numerical calculations in this paper.

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The problem of the stress singularity near the apex in dissimilar materials under surface tractions or thermal loading is considered. In a previous paper, the stress fields with singularity of type γ^P-1 near the apex in bonded two quarter planes under surface traction ω₀ or a uniform temperature change ΔT were theoretically derived. Moreover, the relationship between the stress fields under ω₀ and ΔT was described. However, the stress fields show not only singularity of type γ^P-1, but also one of type log γ. In this paper, the stress fields with singularity of type log γ caused by ω₀ or ΔT are investigated, and a method to obtain the thermal stresses from the stresses caused by ω₀ is presented. In the method, revision functions for each component (γγ, γθ, θθ) of the stress fields caused by ω₀ are added to obtain the thermal stresses, and their functions are shown. Also, the method is verified by the finite element method (FEM).

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The sin² ψ diagram taken from a specimen with steep stress gradients beneath the surface shows nonlinearity because the X-ray penetration depth changes depending on the tilt angle. Stress gradients can be determined from this nonlinearity. Since ceramic materials have a deep X-ray peretration depth, the thickness of a thin ceramic film should have a significant effect on the nonlinearity of the sin² ψ method. In this paper, we propose a method of X-ray measurement of the stress gradient which takes into account of the effect of the thickness of a film under the assumption of linear stress gradients. The film made of silicon nitride was prepared. A 58 μm thick film specimen was carefully polished with diamond slurry to obtain sharp profiles of the X-ray diffraction. To apply the linear stress gradients, the specimen was bent on a cylinder. The stress distribution estimated by the present method agreed well with the applied bending stress, From the present study, stress gradients should be analyzed in terms of the weighted average stress on the basis of the whole intensity of the diffracted X-rays from thin films. when the thickness is less than six times the effective X-ray penetration depth.

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The acoustoelastic spectrum method was applied to analyze plane stress distribution in a U notched aluminum alloy specimen. In the experiment, ultrasonic transverse waves were propagated normal to the surface, and the amplitude spectra of their echoes were analyzed by FFT to find frequency components of null amplitude. From this, two polarization directions and the difference of two transverse velocities were determined. Since the orthogonality of polarization directions thus obtained was a little insufficient, averaging to make them orthogonal proved significant in this stress analysis. Applying these results to the acoustoelastic law of slightly orthotropic materials, the normal stress difference and shear stress were obtained, and each normal stress was subsequently determined by the shear difference method. These stress distributions were in good agreement with the FEM rosults. Since only a few particular frequency components were used in this spectrum method. an improvement using spectral profiles was also considered.

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To study the in vivo damage of the polyethylene acetabular cup retrieved at revision surgery was investigated, Mechanical properties were measured by a viscoelastic spectrometer and a universal Instron type testing machine with a torque meter. The following results were obtained ; 1) There was a positive quadratic correlation between stiffness of the acetabular cup and the duration from the implantation until the revision surgery in the case of the Weber type artificial hip joint. 2) There was a negative qudratic correlation between tan δ and the duration from the implantation until the revision surgery in the case of the Weber type artificial hip joint. 3) There was positive correlation between stiffness of the acetabular cup and the duration from the implantation until the revision surgery in the case of the Kyocera type artificial hip joint. 4) There was a negative correlation between tan δ and the duration from the implantation until the revision surgery in the case of the Kyocera type artificial hip joint. 5) There was a positive correlation between linear wear and the duration from the implantation until the revision surgery in the case of both the Weber and the Kyocera type artificial hip joints. 6) There was a positive correlation between torque and the duration from the implantation until the revision surgery in the case of both the Weber and Kyocera type artificial hip joints.

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The transient process of temperature rise evoked in a viscoelastic body under repeated load is studied analytically and experimentally. Analysis is performed by iterative computation for everchanging heat generation inside the body which is strongly affected by its temperature. Unknown material constants required in the computation, i.e. heat transfer coefficient and temperature-dependent mechanical properties such as viscoelastic modulii of the body, are experimentally determined by heating test and vibration test respectively. Results obtained by computation exhibit good coincidence with those by experiments, notwithstanding the material is in nearly glassy, viscoelastic or rubbery domain.

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One of the uses of coil springs is to keep two structural elements in contact by their mechanical pressure force. When the springs are used in a high-temperature environment, their pressure forces change due to creep. Therefore, it is necessary to analyze creep behavior of coil springs and to estimate the initial pressure force in order to maintain sufficient pressure force during the period in service. First, it is desirable to survey parametrically the creep behaviors of coil springs with various dimensions rather than to analyze the detailed behaviors by FEM. A convenient analysis method of creep behavior of coil springs is presented in this paper. In the development of the method, the torque of the spring is derived based on the assumption of shear stress field, linear distribution of shear strain in the radial direction and the constitutive equation of creep. Finally, the spring force is obtained by the equilibrium equation as a function of time. For implementation of this method, a simple program should be created since the shcar stress distribution in the radial direction is nonlinear; however, a wide-range parametric survey can be done on the creep behaviors of coil springs of arbitrary dimensions and materials.

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In the previous paper, the relationship between the stress rate and the tangent stiffness was derived using the special orthogonal group SO (3) in the finite element formulation. The stress rates used are the Truesdell stress rate, the Jaumann stress rate, the Neo-Green stress rate and the Ishihara stress rate. In this work, the stiffness elements of the tangent stiffnesses of beam elements with SO (3) are given. These elements include material stiffness ΔδП_m, geometric stiffness of rigid rotation ΔδП₁₀, geometric stiffness of stretch to stress direction ΔδП_{sg, stress}, geometric stiffness of stretch perpendicular to area ΔδП_{sg, area} and geometric stiffness of stretch to deformation rate ΔδП_{sg, deform}. In a future paper, the tangent stiffness of these stress rates of a beam element will be given.

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An effective boundary element method with high accuracy for an axisymmetrical electromagnetio field of a layered plate is developed. Quasi-static axisymmetrical Maxwell equations are represented by a vector potential which satisfies the coulomb gauge, and discretized using a standard BEM. Analytical relationships between the magnetic field and the vector potential of an axisymmetrical electromagnetic field are derived for two cases : (1) a layered plate, and (2) a plate whose near-surface conductivity varies as a hyperbolic tangent function of depth. For case (1), the relationship is represented by products of the transfer matrices. For case (2), the relationship is represented by a hypergeometric function. The discrete Hankel transform theory is applied to these analytical relationships, and the result is combined with the standard BEM. The distinct advantage of this method is that discretization is not necessary in a layered plate. It is found that the length of the element that combines the standard BEM with the analytical relationship has a lower limit in this method, because the analytical relationships can be considered as a low-pass filter which relates the magnetic field to the vector potential on the upper surface of a layered plate. The accuracy of this method is demonstrated by solving some example problems.

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A boundary element analysis system using p-version. which is an adaptive mesh refinement scheme. was developed. Generally, elements in the p-version finite element method (FEM) are formulated using the interpolate function based on the hierarchical polynomial and the amplitude of high order function is chosen as the unknown value. In this study, a high-order boundary element that possesses unknown displacements of the collocation point was developed. This element makes it possible to apply the p-version even to contact problems that there are various contact conditions within the element. An effective and efficient error evaluation method suited to the p-version based on stress mode amplitude, in which stress distribution is converted into stress mode amplitude using the hierarchical interpolate function, is proposed. The system was applied to both basic and practical examples and application to actual equipment demonstrated its usefulness.

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We developed an optical birefringence measurement method that uses a photoelastic modulator and a polarized laser. A He-Ne infrared laser was adopted as the light source for measuring the optical birefringence in gallium arsenide wafers. In this paper we explain the theory and the process of measurement of stress in GaAs wafers. The magnitude of principal stress difference and also the directions of the principal stresses were obtained simultaneously and quantitatively using our developed equipment. The optical birefringences of {100} GaAs stressed specimens were measured. From the experimental results, it was found that the photoelastic constant depended on the crystalline orientation and that the birefringence direction did not coincide with the principal stress direction. By stress-strain analysis of the GaAs single crystal, it was found that the birefringence direction coincided with the principal strain direction and that the relationship between the principal strain difference and the birefringence was independent of crystalline orientation.

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The shape fixity and recoverability in a thin film of shape memory polymer of the polyurethane series were investigated using the thermomechanical cycling tests with loadings at various temperatures. The results are summarized as follows. (1) During the heating process under no load, strain is recovered at temperatures in the vicinity of the glass transition temperature T_g in the case of loadings at T_g and T_g+20K, but in the case of loadings at T_g-20K it is recovered at temperatures in the vicinity of T_mg. (2) The rate of strain recovery is about 98%, except for the early cycles in the case of loadings at T_g and T_g+20K, while it decreases with increasing cycles in the case of loading at T_g-20K. (4) The thermomechanical properties of materials with different T_g are quite alike in spite of the difference in T_g.

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Bulk samples of C₆₀ were consolidated by means of the high-pressure technique at pressures of up to 5.4 GPa and temperatures of up to 800°C. The as-pressed samples showed pressure-induced phase transition related to the polymerization. After annealing in a vacuum atmosphere, they converted to the normal phase C₆₀. The mechanical properties such as elastic moduli, compressive strength, hardness, friction coefficient and wear rate were measured. The results indicated the improvement of the mechanical properties in the polymerized phase sample in comparison with the normal phase sample. It was due to the new covalent bond among neighboring molecules in the polymerized phase.

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Semi-solid formings of an AZ91 magnesium alloy containing various sizes and forms of α-phase particles are prepared by a newly developed method. The effects of these structures on the tensile properties and elastic-plastic fracture toughness (J_Q) are investigated in as-cast and in heat-treated samples. The obtained results are as follows : (1) As-cast samples show small values of both tensile properties and fracture toughness regardless of grain size and these are due to the fact that cracks propagate mainly in brittle eutectic compounds. (2) Both tensile properties and fracture toughness of T4-and T6-treated samples increase as grain size decreases. This is assumed to result from the fact that (a) stress concentration at a grain boundary is lower and more twinning deformations occur in a grain as grain size decreases and (b) eutectic compounds are dissolved quickly into the matrix by the short solid solution treatment in semi-solid formings with small grain size.

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Use of a heat engine of which the working elements consists of a shape memory alloy is a useful method for direct conversion of power from low grade heat. The authors have proposed a reciprocating heat engine using shape memory alloy wires. However, in order to undertake reliable engineering designs and optimum material selection, it is imperative that the cyclic behaviors of the shape memory alloy are well understood. In this paper, the cyclic behaviors of Ti-41.7 at% Ni-8.5 at% Cu are investigated experimentally. Experiments are carried out by repeating the combination of the thermal cycle and the loading-unloading cycle under the constant heating and cooling temperature. The results show that the transformation temperatures of M_f and A_s almost do not vary with the number of cycles, but M_s and A_f temperatures increase gradually with cycles when the number of cycles is greater than about 500. It is also noted that two-way strain and irrecoverable strain increase proportionately with the increase in maximum strain. Furthermore, from results of deformation stress in the martensitic phase, the plastic deformation is recognized in the strain range of boyond 4%.

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Cu-9Ti-18B alloy powder was prepared from elemental copper, titanium and boron powders by mechanical alloying for various milling times and hot-pressed in vaccum (VHP). The structural change in the alloy with VHP time was examined and mechanical strength and electrical resistivity of the alloy compact by VHP were also examined. The compactibity in VHP of mechanically alloyed powder was estimated. The density in the alloy compact mechanically alloyed with long milling times were nearly equal to the calculated value. The flexure strength in 3-point bending, hardness and electrical conductivity of the alloy compacts increase with VHP time. These increases are marked in VHP of the alloy powder mechanically alloyed for a long time.

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In a critical compressive state accompanying with deviatoric strain, shear band is observed in soil. On the necking plane that forms a boundary between the shear band and its surroundings, the velocity gradient is discontinuous. This phenomenon indicates that solution is multiple on the necking plane. Plastic instability is known to result from the loss of uniqueness. Hence, the shear band should be analyzed in relation to plastic instability. However, the criterion of plastic instability in soil bas not been investigated in as much detail, as in metal, and attention has rarely been paid to it in the analysis of shear banding. In this study, the comprehensive criterion of plastic instability is discussed and its necessary and sufficient condition is investigated using Cam-clay model. Our previous study on the mode of shear banding showed that only two modes under plane strain rate are parmissible for conformation of the discontinuous velocity gradient on the necking plane. Taking this into account, the criterion consists of three cases, that is, a statical case and two kinematical cases. These cases are characterized by h=0 where h means the hardening modulus, and the plane strain rate censtraint is added to in the kinematical cases. Furthermore, it is shown that the shear band cannot make any angle other than 45 degrees from the principal compressive axis, even if the yield locus on the deviatoric plane is modified.

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In the previous report, we presented an optimization algorithm of two-dimensional structure subjected to a plastic deformation, where an admissible domain is assumed to be composed of microstructures with regular triangular cavities and the local cavitation size and rotation angle of the microstructure are determined so as to minimize the work done by the applied load. In this paper, several numerical examples are presented to demonstrate the validity of the algorithm. It is shown that the obtained material distribution is different from that obtained by the elastic analysis especially when a plastic hinge takes place by bending. Optimization analysis using microstructures with square cavities is also conducted to examine the effect of the shape of the microstructure, where the ultimate obtained strength increases slightly while material distribution remains essentially the same.

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The paper presents a method for evaluating the dispersion and reliability of structural analysis using a statistical optimization method that consists of effectivity analysis and optimization. The effectivity analysis is used to generate approximate evaluation functions for the behavior of an object structure. A first-order second-moment method is employed to evaluate and generate approximate evaluation functions for the dispersion of the behavior. A successive quadratic programming (SQP) method is employed to solve the optimization problem using the approximate evaluation functions of the behavior with dispersion. A reliability index β, β^* and the upper bound of failure probability obtained using the second moment method are employed in the reliability evaluation of the object structure with a set of design parameters. It is confirmed that the proposed method can be used for almost all kinds of nonlinear problems including the impact behavior of structures, and that the number of finite element analyses based upon the proposed method is much smaller than that of other existing methods.

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A box structure CAE system was developed in order to reduce production cost, box weight, and design time. This system assists the user in developing an initial design using a neural network; modeling the box structure for FEM analysis; optimizing the box structure by sensitivity analysis; and assembling a database for the box structure. When we applied this system to a sample weight minimization problem, the box structure weight was reduced by 36 percent. Furthermore, we predicted the displacements and shape of the box structure using a neural network.

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