The complex deterioration on fatigue reliability at elevated temperature for carbon-fiber-rein-forced PEEK was examined. In particular, the influence of thermal and mechanical fatigue on the fatigue mechanism of a sharp notched specimen was focused on. The main results were as follows. (1) An S-N curve was formed as a polygonal line having a downward convex regardless of the environmental temperature and fiber content. For long fatigue life, the influence of the carbon-fiber-content on fatigue strength was more remarkable than for a short fatigue life. (2) From fractography using SEM (Scanning Electron Microscope), temperature rise and cyclic deformation measurements, it was found that the fatigue mechanism for short life (N_f<10⁵) is thermal fatigue, while one for long life (N_f>10⁵) is mechanical fatigue. (3) The resistant mechanism against FCP (Fatigue Crack Propagation) in thermal fatigue is the capability to convert from strain energy into thermal energy, while that of mechanical fatigue is the bridging effect of reinforced fiber.

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An experimental study was carried out with the aim of development of a fatigue reliability design method for surface modification components using two types of specimen consisting of homogeneous and heterogeneous materials. The main results obtained are as follows : (1) The fatigue reliability of the surface modification material could be estimated using an "S-N Globe". (2) The degree of scatter of the fatigue life on the "S-N Globe" could be estimated from probability characteristics of the mesoscopic factor at the crack initiation site. (3) A "P-S-N Globe" was created by combining the experimental analysis with the mesoscopic fracture mechanics and reliability engineering. This concept represents a major contribution to the fatigue reliability design method for surface modification components.

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In order to investigate the effect of surface roughness on fatigue strength, fatigue tests for a medium carbon steel, which was annealed and free of residual stress (HV&cong;170) and quenched and tempered (HV&cong;650). were carried out. To simulate the actual surface roughness, extremely shallow periodical notches with a constant pitch but irregular depth were introduced. The equivalent defect size √(area)_R for roughness was defined to evaluate the effect of irregularly shaped roughness using the √(area) parameter model. The fatigue limits of the annealed medium carbon steel specimens with artificial surface roughness are much higher than those of the specimen with a single notch because of the interference effect of notches. The fatigue limits predicted by the √(area) parameter model are in good agreement with the experimental results.

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Axial loading fatigue tests were carried out for annealed 0.45% carbon steel at various stress ratios. When the stress level is high, the crack growth rate is expressed by the small crack growth law. dl/dN=Cσⁿl (dl/dN : crack growth rate, σ : nominal stress amplitude, l : crack length, C and n : constants) at each stress ratio, though the constants C and/or n in the crack growth law vary depending on the stress ratio. On the other hand, the crack growth rates are determined independently of the stress ratio by the modified crack growth law, dl/dN=C'ε_p^n'l. where ε_p is the plastic strain amplitude obtained from the cyclic stress strain curve at each stress ratio, and C' and n' are constants.

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Near-threshold fatigue crack propagation tests were performed on circumferentially precracked round bars of medium carbon steel under mode III torsional loading. The crack propagation rate was decreased with crack extension because of the shear contact of the crack faces. The crack propagation rate without the influence of crack surface contact was determined by extrapolating the relationship between the crack propagation rate and the crack extension to the zero crack extension. The applied stress intensity factor range was divided into two parts : one was the effective value which was responsible for crack growth and the other was the shielding value. The resistance curve method was used to predict the fatigue limits for crack initiation and fracture. The R curve was constructed using the experimentally determined threshold value of the stress intensity range which was the sum of the threshold effective stress intensity range and the threshold shielding stress intensity range. The threshold effective stress intensity range was constant. The R curve was independent of the crack length and specimen dimensions. The predicted values agreed well with the experimental results.

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Fatigue crack growth resistance was greatly increased due to inclusion of glass beads, CTBN and CNBR modifications at the second stage of the crack growth (da/dN=10^-4-10^-3mm/cycle), although an increase in the observed toughness depended on the inclusions. The resistance of the CNBR-modified adhesive was higher than that of the glass-bead-reinforced and the CTBN-modified adhesives at this range. However, the energy release rate at threshold for both CNBR-and CTBN-modified adhesives was lower than that for the unmodified adhesive. In particular, the threshold reduction for the CNBR-modified adhesive was remarked while the threshold reduction for the glass bead-reinforced adhesive was slight. The effect of adhesive thickness on fatigue crack growth decreases due to CTBN and CNBR modifications. Fracture surface observation revealed that the fatigue crack growth mechanisms in all toughened epoxy adhesives involved some crack path deflections. Adding glass beads to CNBR-modified adhesives improved the threshold reduction.

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In this study, fatigue reliability of the tube which is used in brake equipment was examined in terms of fatigue fracture with internal pressure. The characteristic of fatigue life distribution of the tube was investigated from the results of internal pressure fatigue test and the fatigue reliability of the tube was evaluated by FEM analysis. The main results obtained were as follows ; (1) From internal pressure fatigue test, it was confirmed that fatigue strength of the tube was reduced as smaller radius of curvature by bending. (2) It was found that profile of the section of tube was collapsed circle and crack was initiated on base of the welding bead. (3) From the evaluation of statistical fatigue life, it was confirmed that fracture of the tube was only caused by initiating crack on base of the welding bead. (4) According to the S-N curve, it was understood that the stress amplitude that guarantees the safety of the tube is 100 MPa. This stress amplitude correspond to the fatigue limit of mild steel. (5) The suitable forming of tube can be determined by using the diagram of the relationship between radius of curvature and safety internal pressure.

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Finite-element analysis was performed to characterize the deformation behavior of ceramic composite material during static and dynamic bending. Normal and shearing stress distributions were clarified by FEM with respect to elastic anisotropy and the specimen height-to-span ratio, (H/L), and the tensile and shearing fracture behaviors were well understood in comparison with the predicted stress distributions. It is determined that well-ramped impact bending leads to almost identical stress distributions as static bending and, consequently, the fracture strength of brittle materials can be measured at a high deformation rate. Tensile and shearing strengths were significantly increased with the rise in the deformation rate.

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In this paper, we present the Green's functions for a steady state heat source in a transversely isotropic thermoelastic solid by means of a displacement function method when the functions are expressed as the Cartesian coordinates. The solutions for the solid can be classified into five cases corresponding to the roots of our characteristic equation, which shows the relationship between the elastic constants and the coefficients of thermal conductivity. The solution for the isotropic solid is included as a special case which corresponds to a triple root of our characteristic equation. Furthermore it is noted that the solutions for the double root in our characteristic equation include the solution in which there is a relationship between the coefficients of thermal conductivity and the elastic constants. Finally, the numerical results are given.

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This paper deals with numerical solutions of singular integral equations in interaction problems of rectangular inclusions under various loading conditions. The body force method is used to formulate the problems as a system of singular integral equations with Cauchy-type or logarithmic-type singularities, where the unknown functions are the densities of body forces distributed in infinite plates having the same elastic constants as those of the matrix and inclusions. In order to analyze the problems accurately, the unknown functions are expressed as piecewise smooth functions using two types of fundamental densities and power series, where the fundamental densities are chosen to represent the symmetric stress singularity of 1/r^1-λ₁ and the skew-symmetric stress singularity of 1/r^1-λ₂. Then, newly defined stress intensity factors at the end of inclusions are systematically calculated for various shapes and spacings of two rectangular inclusions in a plate subjected to longitudinal tension, transverse tension, and in-plane shear. The present method is found to be effective for accurate and efficient analysis of rectangular inclusions.

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In this study, analysis of phase spectra of ultrasonic transverse waves is shown to be a reliable new method of acoustoelastic stress measurement. At first, phase spectra of birefringenced transverse waves were theoretically analyzed, and the difference in phase spectra corresponding to two mutually orthogonal transducer directions was introduced. Then, a method of curve fitting to this difference was used in order to determine the polarization directions and velocity difference of transverse waves. From this, it was confirmed that no particular transducer directions were required for this determination. Finally, this method was applied to stress analysis of a V-notched specimen subjected to four point bending, and the normal stress difference and shear stress were determined along several lines of the specimen.

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The internal residual stress distribution that resulted from welding a 4-inch-diameter carbonsteel pipe butt joint was evaluated using several methods and the results were compared. The analytical evaluation methods used were inherent strain analysis and thermal elastic plastic analysis, and the experimental methods were X-ray diffraction and strain gauge for the surface residual stress, and neutron diffraction for the internal stress. The residual stress distributions determined using the various methods agreed well with each other, both for surface stress and internal stress. The characteristics of the evaluation methods were summarized and it was found the most suitable method for any particular situation can be selected by considering the evaluated location and the operating conditions of the object to be evaluated.

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The residual stress distribution of ground ceramics was determined from the eigen strain existing in the ground surface. The eigen strain of ground ceramics was tensile, and exponentially decreased with the distance from the surface. The residual stress distribution is given as a superposition of an exponential function of compression and a linear function. It is found that the actual residual stress distribution can be approximated by a compressive exponential function because the magnitude of tensile residual stress is negligibly small compared to the compressive residual stress. In the experiments, the diffraction angle was measured on ground silicon nitride for a wide range of sin²ψ using the glancing incidence X-ray diffraction technique. A strong nonlinearity was found in the 2θ-sin²ψ diagram at very high ψ-angles. From the analysis of nonlinearity, the residual stress distribution was determined. The residual stress distribution of silicon nitride coincided with the distribution calculated from the eigen strain distribution. Transmission electron microscopy was used to clarify the origin of generation of the residual stress. Both strain contrasts and microcracks were observed below the ground surface ; straight dislocations were also observed within silicon nitride grains near the ground surface.

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High temperature and high pressure water corrosion behaviors of ZrO₂-particle-dispersed Al₂O₃ composites were investigated in terms of with the microstructural changes and residual strength characteristics. Sintered Al₂O₃ bodies with 5, 15, and 30 wt.% 3 mol% Y₂O₃-doped tetragonal ZrO₂ were made using a pressureless sintering method at 1 550. 1 600 and 1 650°C, respectively. These Al₂O₃/ZrO₂ ceramic composites were corroded in high temperature and high pressure deionized water at 200°C∼300°C. Corrosion damage of the Al₂O₃/ZrO₂ ceramic composites occurred preferentially on ZrO₂ particles after long-term immersion in deionized water. The tetragonal to monoclinic phase transformation occurred in yittria-doped tetragonal ZrO₂ polycrystals due to high temperature and high pressure deionized water corrosion. For improvement of the corrosion characteristics of the composites, are important increasing the ZrO₂ content within a range in which no remarkable residual strength degradation is recognized and lowering of the sintering temperature. Al₂O₃/ZrO₂ ceramic composites also have superior residual strength characteristics compared to monolithic ZrO₂ ceramics. The residual strength characteristics are improved by increasing the ZrO₂ particle concentration. and loweringthe sintering temperature. The fracture surface morphology change from transgranular to intergranular was brought about by increasing the ZrO₂ content. Improvement in residual strength characteristics of Al₂O₃/ZrO₂ composites was realized. due to intergranular crack propagation, crack pinning caused by remarkable grain bridging by Al₂O₃ and stress-induced transformation from tetragonal ZrO₂ to stable monoclinic in the vicinity of the crack tip. Then, the necessary manufacturing conditions for sustaining the improved strength characteristics after high pressure and high temperature water immersion were clarified. In addition design concepts used to obtain water-corrosion-resistant high strength and high toughness particle dispersed ceramic composites were proposed.

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In previous papers, microscopic expression of stress and balance equations for a solid which has a simple lattice were described with the microscopic values in the mesodomain without an assumption of a constrained gradient. In this paper, the solid is remodeled as an assembly of atoms which are arranged randomly. Microscopic expressions of stress. higher-order stress and heat flux are newly discussed expressing the equilibrium conditions for the tetrahedral element in the mesodomain. Stress is represented as an area averaged values with microscopic quantities such as interatomic potential, body force, inertia force and fabric vectors related to the configuration of atoms in the mesodomain. Balance laws of momentum and moments of momentum are derived on the basis of the equations of the motion of atoms. The energy equation is described with the averaged values over the domain dividing the velocity of an atom into the macroscopic motion and thermal motions.

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This paper deals with numerical solutions of singular integral equations in the problem of an elastic cylindrical inclusion with ends in an infinite body under tension. The problem is formulated as a system of singular integral equations with Cauchy type or logarithmic type singularities, where unknown functions are densities of body forces distributed in infinite bodies having the same elastic constants as those of the matrix and inclusion. In the numerical analysis, the unknown functions of the body force densities are expressed as a linear combination of two types of fundamental density functions and power series, where the fundamental density functions are chosen to express the symmetric stress singularity of the form 1/r^1-λ₁ and the skew-symmetrics stress singularity of the form 1/r^1-λ₂. Then, the singular stress fields at one end of a cylindrical inclusion are discussed for various fiber lengths and elastic ratios. The results are also compared with ones for a rectangular inclusion.

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In the previous papers, 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 that work, the stiffness elements of the tangent stiffnesses of beam elements with SO (3) were given. Those elements include material stiffness ΔδΠ_m, geometric stiffness of rigid rotation ΔδΠ, geometric stiffness of stretch to stress direction ΔδΠ, geometric stiffness of stretch perpendicular to area ΔδΠ and geometric stiffness of stretch to deformation rate ΔδΠ. In this paper, post-buckling analyses are made using the beam element of Ishihara stress rate. It is shown that the results are almost the same as the results of both 2-dimensional and 3-dimensional analyses of elastica, because the beam element has only geometric stiffness of rigid rotation as geometric stiffness and it can exactly show the nonlinearity of rigid rotation. It is also shown that the beam element without SO (3) can't be used for 3-dimensional large rotation analysis.

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A formulation for finite element interval analysis with respect to identification of external loads on the basis of uncertain displacement input under the assumption that the stiffness matrix of the structural system of interest is known with certainty in problems of linear, elastic structures subjected to static loading is proposed. The input nodal displacements are assumed to include uncertain error, and the error is assumed to be confined in a convex hull. The governing equation of the uncertain nodal displacements that indicate the interval of nodal forces is derived from the results of sensitivity analysis with respect to uncertain displacements, and is solved using the Moore-Penrose generalized inverse. The results of the interval analysis are verified by a simulation for an elastic, square plate under multiple loads.

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We present a method of damage identification of symmetrically laminated plates using bending deflection under static loading. The location of damage is first identified using an equation error approach based on residual forces. Then the magnitude of damage is evaluated using the nonlinear optimization technique. The effect of the number of measured deflection data on the identification results of the location and the magnitude of damage for symmetric laminates with one or two damage elements is examined.

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The use of bellows expansion joints is an effective method to rationalize various piping systems in industry. In the structural design, the requirements for preventing failures such as ratchetting, fatigue, and buckling should be satisfied. The mechanisms of some failure modes of bellows are different from those of vessels and piping components. It is a particularly unique characteristic that bellows buckle under internal pressure. In the case of hightemperature operation, the possibility of creep buckling should be considered. The author has proposed an evaluation method for column-type creep buckling of bellows under internal pressure. In this study, the creep deformation behaviors of bellows are investigated using finite element nonlinear analyses and the validity of the evaluation method is discussed.

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Creep damage modeling from the combined viewpoints of macroscopic and microscopic levels is proposed. A damage variable of a second-rank tensor for each material point is defined by the cavity microstructure of the grain aggregate simulated by the Voronoi tessellation. The damage evolution is calculated from the nucleation and growth of the grain boundary cavities using physically based equations. Furthermore, the effects of creep damage on mechanical behavior are treated at the macroscopic level by the damage mechanics formulation. The results of the analysis show that the rate of the damage evolution decreases at the final stage of damage.

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No method with which to characterize and/or illustrate total creep behavior for specimens with notches, holes or cracks has been proposed. In this paper it is proposed that most creep curves can be drawn with a master curve for each creep test whenever test conditions and failure modes are similar to each other, and the lifetime ratio normalized by the rupture time is introduced. Using smooth and circumferentially notched specimens of 2.25 Cr-1 Mo steel, creep tests were performed at 600°C for examination of this concept. Furthermore, a θ projection method was used to describe creep curves for notched specimens and to extrapolate longer creep lives. Then, the whole creep curve shape for notched specimens could be easily drawn, except for that in the vicinity of the rupture point. However, longer creep lives of notched specimens were underestimated in comparison with a simple extrapolation of the experimental data. This resulted from the negative dependence of the parameter of θ₃ on the applied stress.

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A three-dimensional finite element computer program was developed to deal with the thermal stress analysis of a gadolinium ortholilicate (Gd₂SiO₅, hereafter abbreviated as GSO), a monoclinic single crystal, during the Czochralski growth process. A GSO single crystal has strong anisotropy in the elastic constants and thermal expansion coefficients, so three-dimensional analysis is required for the exact calculation of the thermal stress. A tensor transfomation technique was used to obtain the components of the elastic constant matrix and the thermal strain or thermal expansion coefficient vector corresponding to an arbitrary pulling direction. Using this computer program, we performed the thermal stress analysis of a GSO bulk single crystal for various pulling directions to examine the relationship between the magnitude and distribution of the thermal stress and the pulling directions. The b-axis pulling of a GSO bulk single crystal was proposed from the viewpoint of minimizing thermal stress during the growth process.

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In this paper, application of the homology theory, which is a field of mathematics concerned with topology, to structural optimization is attempted. A homology group, which is one of the Abelian groups, can represent the topology of a structure in a standardized way ; that is, the canonical direct sum decomposition. Therefore, topological information of a structure can be described in the formulation using homology groups. An abstract combination problem of triangular elements is chosen as a numerical example to verify the generality of this method using the homology theory. Several of the triangular elements are combined into a structure. Under the topological constraint condition represented by homology groups, a structure which has the minimum sum of numbers of triangular elements, its sides, and its vertices, is found by genetic algorithm. Furthermore, homology groups are utilized to describe the fitness function in the genetic algorithm as another example.

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In this paper, the structural design and analysis of a FRP pressure vessel with a load-carrying metallic liner are presented. First, an outline design of the vessel is obtained utilizing netting analysis and membrane theory, and the shape of the dome is determined based on the concept of isotensoid. Then, FEM analysis is employed to clarify the stress state in the vessel and to obtain a higher structural efficiency. Here, the liner is modeled with shell elements and the FRP is modeled with offset shell elements. Using the above methods, S-glass FRP vessels with aluminum alloy liners are manufactured experimentally. Autofrettage and single-cycle burst tests are conducted using hydraulic fluid pressurization. Good agreement between calculated and measured results is obtained.

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A method is proposed for structural optimal design under multiple loading conditions based on the game theory in combination with finite element analysis. Two players are supposed to play the zero-sum game, one having design strategies for minimization of payoff defined as the mean value of free nodal displacements, and the other using loading condition strategies to maximize it. Optimal design strategies are compared repeatedly as the game value by means of solution of a linear programming problem derived from the table of payoff. The validity of the proposed method for the optimum design under multiple loading conditions is demonstrated by the numerical examples of plane frame structures.

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This paper outlines an improved simulation method for a time-dependent reliability analysis of structural systems subjected to stochastic loads. Strengths of structural elements are assumed to degrade with time proportionally during the life cycle of the structural system, and stochastic load events are modeled as Poisson processes. The structural failure probabilities are estimated through the life cycle simulation, in which the directional simulation method is applied just to sample random load variables to execute each life cycle simulation efficiently. Numerical examples are presented and results are compared with those obtained by the crude Monte Carlo simulation to show the effectiveness of the proposed method. It is shown that the proposed method is effective for the assessment of the time-dependent failure probability of structural systems.

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This paper describes a new method for evaluating the probability of structural failure based on a directional vector approximation. Since failure probability is defined by a directional integration of the conditional failure probability evaluated as the upper probability of a chi square distribution in the specified direction, it is evaluated by the summation of the product of the area of the finite element mesh and the upper probability of the chi square distribution corresponding to each element mesh. The directional vectors are detemined by adopting the unit centerline vectors related to finite element meshes allocated regularly on the surface of the unit sphere, which is divided analytically into a specified number of finite element meshes. The proposed method gives good estimates of the structural failure probability. Numerical examples are provided to show the validity of the proposed method.

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The effects of the shrinkage of adhesive resin on the dimensional accuracy of optical elements during curing were investigated analytically and experimentally. The optical elements of a lens and a holder bonded with epoxy resin were treated. The lenses were made of glass or polymethylmethacrylate (PMMA). The shrinkage and changes in the mechanical properties of the adhesive resin during curing at room temperature were measured. The strain distributions of the lens and its deformation were calculated using the finite element method, considering the viscoelasticity of the adhesive resin. The deformations of the lenses were measured using strain gauges and an interferometer. The measurement results of strain distribution qualitatively agreed with the analytical results. It was shown that the shrinkage of the epoxy resin caused the deformation of the lens, and the changes in the mechanical properties of the epoxy resin largely influenced the magnitude of the deformation.

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In order to evaluate the grade of metal bonded synthetic diamond, it is useful to examine the shape of diamond grains using scanning a electron microscope. Distribution of the largest and smallest diameters of the grain obey normal distribution as a first approximation. The grains comprise a mixture of cubes and octahedra, and it is observed that {100} and {111} planes construct the cubic and octahedron planes, respectively. Then, we defined various kinds of shape coefficient that denotes the magnitude of deviation from a sphere, which showed good correlation with the strength of the diamond. Therefore, the magnitude of strength of diamond can be examined using the shape coefficients defined here.

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The effect of heat treatment on the strength of Cr₃C₂-20%NiCr coatings sprayed on 13%Cr-5% Ni steel by high-velocity oxygen fuel (HVOF) spraying has been studied. Specimens were heated to 823 K and held for 1, 5, and 15 h. The strength and hardness of Cr₃C₂ 20%NiCr-sprayed coatings were measured by a tensile test and a micro-Vickers hardness test. The results obtained were as follows. (1) Heat treatment increased the strength and hardness of the Cr₃C₂-20%NiCr-sprayed coatings. (2) The treatment decreased the maximum peeling area on the 13%Cr-5%Ni steel base under the cracks produced in tensile tests. (3) The mechanism of the strengthening of Cr₃C₂-20% NiCr sprayed coatings by heat treatment is considered to be as follows. The heat treatment divides the blowhole cracks in the coatings into smaller subvoids and decreases the extension paths of steel base, thus strengthening the adhesion force and hardening the sprayed coating.

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This study was conducted to clarify the effect of CO₂ laser irradiation on the wear resistance, corrosion resistance and fatigue strength of Ti-6Al-4V alloy. The results are as follows. (1) Laser irradiation results in formation of a hardened case on the titanium alloy because precoated carbon, oxygen and nitrogen existing in the air rapidly diffuse to the inside during the irradiation. The formation of such a hardened case greatly improves the wear and corrosion resistance of the titanium alloy. (2) Laser irradiation results in a marked decrease in the fatigue strength of the titanium alloy. This is caused by (i) cracking on the surface during the irradiation, and (ii) change of the fine equiaxed microstructure to the widmanstatten microstructure.

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Recently, the development of an optimum forming process design system based on computer-aided technology has been required to reduce both time consumption and cost. The authors have developed an optimum forming process design system based on a concept which integrates the FEA and the numerical optimization method. In this design, an objective function has several local optimum points, and it is necessary to find the global optimum point. Therefore, in this paper, the sweeping simplex method is proposed, which finds the global optimum point efficiently. The proposed method was applied to a drawing process design. In order to obtain products with uniform thickness, two-stage drawing was employed. Two values of punch heights which characterize the first-stage punch shape were chosen as the design variables, and deviation of thickness from the average thickness was chosen as an objective function. It was demonstrated that the system could find the optimum condition efficiently. Furthermore, the optimum condition evaluated by the proposed system was verified to be in good agreement with the experimental results.

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This paper describes the effect of crystal orientation on the machinability of the atomic-scale cutting process by molecular dynamics simulation. The interatomic force between tool and workpiece is assumed to be derived from the Morse potential function using parameters based on the abinitio molecular orbital calculation for a NiC₆H₉ cluster. Molecular dynamics simulations of the cutting process were carried out by changing the surface gradient angle θ and the cutting direction angle θ. The angle θ significantly influenced the chip and side flow formations, while the angle φ did not. The atomic-scale cutting on the surface in the negative θ region brought about a smoother surface than that in the positive θ region. The angle θ influenced the number of workpiece atoms moved while the angle φ had an influence on the moving direction of the workpiece atoms. We found that the best machinability in the atomic- scale cutting process occurred when the angle θ was more than 0°, with the cutting direction being near the slip direction of the workpiece.

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