AE (Acoustic Emission) generation behavior during microfracture process of 2-dimensional alumina polycrystals is simulated by assuming that a microfracture corresponds to an AE event. Various AE generation behaviors are predicted as a function of the grain boundary toughness (K_cb), the grain size and the distribution state of residual stresses due to crystalline anisotropy. The predicted AE events have a tendency to occur at higher stress with increasing K_cb and with decreasing grain size. By the fracture-mechanical calculation of the crack opening volume, the relative variation of AE amplitude is also simulated. The actual AE measurements are carried out in vacuum for the two kinds of alumina with-different grain size, and compared with the simulated results. The cumulative AE event curve for 11.5 μm grain size shows good agreement with the simulation when the K_cb is 0.35 times the grain toughness (K_cg), and that for 28.2 μm shows good agreement with the simulation at K_cb=0.45K_cg. The results of AE location for both the simulation and the measurement show the similar characteristics of the scattered distribution over the stressed fields.

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The degree of the enhancement of the fracture resistance of an orthogonal three-dimensional composite of carbon fiber reinforced epoxy is experimentally determined using a DCB testing method. By analyzing the load-displacement curve and the energy change caused by the breaking of the bridging fiber yarn, the mechanism of the bridging enhancement of the fracture resistance is considered. It was found that the greater the number of bridging yarns in the crack, the greater is the amount of deformation energy per cracking area necessary for crack propagation. An estimation method for the mode I fracture toughness of the material is presented.

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Silica-particulate-filled epoxide resins are used as encapsulant materials in semiconductor packaging. In the present paper, the effects of moisture absorption on the bending strength and fracture toughness of two types of the epoxide resins containing 70wt.% silica particles have been studied. The bridge indentation method was employed in precracking of specimens. The fracture toughness obtained agreed well with the results of fatigue precracked specimens. The fracture toughness of both resins slightly increased with moisture absorption while the bending strength tended to decrease. Fracture surface observation by scanning laser microscope shows that debonding of the interface between silica and epoxy predominates in the fracture surface of the bonding specimens while cracking of silica particles triggers the fracture of the precracked specimen. It is suggested that differences in bending strength and fracture toughness due to moisture absorption are attributable to differences in the stress triaxiality of the specimens.

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Effects of 3 mol% Y₂O₃-doped tetragonal zirconia polycrystalline addition upon the mechanical properties and microstructure of Al₂O₃ were investigated. Al₂O₃ specimens containing 5wt.%, 15wt.%, and 30wt.% of 3mol% Y₂O₃-doped Z_rO₂ were prepared by the sureless sintering method at 1 550°C, 1 600°C, and 1 650°C. Then, the bending strength and fracture toughness (K_c) were evaluated, and the microstructure of these composites were examined. Addition of Z_rO₂ to Al₂O₃ greatly improved the bending strength, fracture toughness and hardness. It was found that, the bending strength and fracture toughness were maximum when the content of Z_rO₂ was 30wt.%. Specimens sintered at 1 650°C indicated inferior mechanical properties due to grain growth. Through X-ray diffraction pattern analysis, examination of the phase transformation of Z_rO₂ from tetragonal structure (t-Z_rO₂) to monoclinic structure (m-Z_rO₂) was conducted. In the case of the composite specimen containing 3Owt.% Z_rO₂, the most marked phase transformation was recognized. Substantial grain bridging was observed in the crack growth behavior of composite containing 3Owt.% Z_rO₂ and sintered at 1 550°C.

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In order to improve the interlaminar properties of C/C composites, SiC whiskers were added to the carbon matrix. C/C composites with 0, 2.5, 5.0 vol.% of SiC whiskers were examined by short beam shear, DCB and ENT tests. Other mechanical properties, such as flexural and tensile properties, were also evaluated for each specimen. Results showed that SiC whisker addition drastically improved interlaminar shear strength (ILSS) and interlaminar fracture toughness, though C/C composites with 5.0 vol.% of SiC whiskers showed a 20% decrease in tensile strength. Observation of microstructure and crack extension during fracture toughness tests revealed that main effects of SiC whisker addition were reduction in density of intrinsic cracks and change in fracture mode mainly due to reinforcement of the fiber-rich layer/matrix interface.

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This paper deals with a method of changing fiber orientations or thickness of plies in order to satisfy flexibility constraints imposed on fiber-reinforced plastic (FRP) laminated plate. The flexibility matrix of the laminated plate is defined as the inverse of the stiffness matrix, and its sensitivities with respect to design variables are computed in the context of the finite element method. Several components of the flexibility matrix are shifted to their prescribed values by a modified Newton's method. The numerical examples to demonstrate the validity of the proposed method are concerned with graphite/epoxy laminated plate. First, homologous deformation is investigated to check the proposed method with six plies, using six fiber orientations as design variables. The possibility of passive deformation control free from variability of magnitude and mode of loading is investigated by setting two flexibility components equal to zero in the second example. The effect of ply thickness change is also investigated numerically.

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Delamination in CFRP plates frequently occurs due to the transverse loading. The purpose of this study is to establish an estimation scheme of delamination in a CFRP plate by evaluating the delamination toughness between laminates. Both experimental and numerical studies are conducted. Delamination occurs at the interlaminar region where the fiber orientation changes. The delamination toughness is evaluated by a three-dimensional finite-element method. Analyses are conducted assuming a single delamination in a plate. Distribution of the J-integral along the crack front is larger on the parallel part of the delamination. The average of the J-integral on the parallel part of the delamination is obtained and defined as delamination toughness. The delamination toughness changes with change of fiber orientation. Finally, the shape of delamination is estimated numerically.

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In the previous paper, micromechanical analysis was performed for a particle-reinforced composite with crack-bridging particles of various radii, by both introducing the stereological concept to the micromechanical model and considering interfacial debonding between a particle and a matrix. The expressions of energy release rates for both a matrix crack and a debonding crack were obtained. In the present paper, the criteria of crack propagation for matrix and debonding cracks are derived by adopting Griffith's concept for crack propagation. The critical length of the matrix crack, a_c, whose propagation will be arrested, can be obtained, which implies that the fracture toughness of such a composite can be evaluated using this criterion. The effect of material parameters such as the volume fraction of particles, the length of debonding, and the distribution of the radii of the particles, etc., on the toughness can be explained by the interfacial phenomenon. The results obtained are consistent with typical experimental findings.

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Explicit expressions for in-plane mixed-mode asymptotic solutions of an unsteadily fast-propagating crack tip had not been derived so far, due to seemingly insurmountable mathematical and algebraic difficulties To overcome these difficulties, a symbolic manipulation system was used in the present study. The explicit expressions for the mixed-mode transient stress and displacement fields up to the first five terms (n=0∼4) in asymptotic series were successfully derived. It was found that the transient effects do not appear in the first three terms (rigid body (n=O), singular (n=1) and constant-stress (n=2) terms), but appear only in the higher-order terms greater than or equal to the third order (n≥3). The transient effects in the near-tip stress distributions were also visualized using the symbolic manipulation system. It was found that both effects of the crack acceleration and of the changes in the asymptotic coefficients increase the stress distribution ahead of the propagating crack tip. These stress-increases in the unsteady part may clarify the problem of the crack-acceleration effects in the dynamic fracture toughness versus crack velocity curves, which is one of important unsolved problems in dynamic fracture mechanics.

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In order to develop a cutting tool and estimate structural reliability of optical glass fiber, the fracture behavior of toughened fiber treated with Ti dope was examined through fractography and the acoustic emission method. As a result of investigating the fractography of a fiber observed by SEM in relation to maximum amplitude and peak frequency of the AE pulse, it was experimentally shown that an entirely mirrorlike end of the optical glass fiber could be produced only when the maximum amplitude of AE pulse was small, and the peak frequency was low. Furthermore, both the compressive stress remaining in the fiber and fracture stress during cutting were estimated theoretically. The optimum size of cutter cracked defects was clarified from the viewpoint of fracture mechanics, so as to produce an entirely mirrorlike end of optical glass fiber. Thus a new method for evaluating the mirror quality end of optical fiber available for light communication by detecting the AE pulse emitted on cutting was developed.

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Because of its excellent mechanical properties at elevated temperature, a nickel-base superalloy has been widely used in the aerospace industry and nuclear power plants. In this study, rotating bending fatigue tests were carried out for Inconel 718 at room temperature and elevated temperatures of 300°C, 400°C and 500°C to investigate the notch sensitivity at the elevated temperatures. It was found that the fatigue limits of plain specimens were higher at the elevated temperatures than at room temperature, which might be due to the suppression of the crack initiation at the elevated temperatures, however, the resistance to crack growth became smaller at the elevated temperatures than at room temperature. Therefore, the fatigue strength of a notched specimen, in which a crack initiated easily owing to the stress concentration introduced, was lower at the elevated temperatures than at room temperature. Consequently, the fatigue strength reduction factor was larger at the elevated temperatures than at room temperature.

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The fatigue reliability of recycled advanced fiber-reinforced thermoplastic resin (FRTP) was examined In particular the effects of mesoscopic factor on the fatigue crack propagation in PA·46 were considered. Main results obtained as follows: (1) The FCP property of recycled PA·46 was inferior to that of the virgin material. It appears that the detrimental effect of recycling on fatigue property was caused by break-up of the glass fibers during the recycling process. (2) By the thermal method using infrared thermography, it was found that the FCP property of each specimen was related to the crack tip opening displacement. (3) It was found that FCP property in the higher FCP rate range was related to the bridging effect. This was because the FCP property of CF material is superior to that of GF material.

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The influence of SiC particles on fatigue crack propagation (FCP) in SiC particles/6061 aluminum alloy composite was studied. The main results were as follows. (1) In the IIa region of a FCP diagram and at the threshold value ΔK_th, the FCP property was controlled by ΔK (the effect of cyclic loading). (2) In the IIb region of the FCP diagram, the FCP property was controlled by K_max (monotonic maximum loading). (3) In the IIa region of the FCP diagram, the fatigue crack went around SiC particles and through an aluminum matrix. Then, the threshold value ΔK_th became equal to the value of ΔK under which the dimensions of cyclic plastic zone at the crack tip were the size of SiC particles. (4) In the IIb region of the FCP diagram, FCP was accelerated by SiC particle cracking which was a brittle-like monotonic fracture.

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Quasi-static and fatigue tests of single-crystal silicon microelements fabricated by micromachining (photoetching) were performed. The cantilever-beam microelements were subjected to simple bending using a specially designed testing machine. Extremely small loads could be applied to a microelement by means of an electromagnetic actuator, and quasi-static and fatigue tests could thereby by performed with sufficient precision. Silicon microelements deformed elastically until final catastrophic failure, giving a brittle nature. The fracture strengths increased with decreasing specimen size. Fatigue tests were performed, and the influence of water on fatigue strength was discussed. The fracture surface and sample surface were examined in detail using a scanning electron microscope (SEM) and an atomic force microscope (AFM), and the fracture mechanisms were discussed.

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This paper discusses the stress singularities around a crack in the two dimensional elastic materials. Based on Williams' method of the eigenfunction expansions, the crack tip singularities for various open crack and material combinations are computed for plane problems as well as for antiplane problems. The order of singularities is discussed for the cases of modes I, II and III. The intensity of stress singularity and the stress and displacement modes are shown, and the characteristic features of the stress singularities are discussed It is found that stresses have the singularity of the form γ^i-1, where γis the distance from the crack tip, and the exponent λ lies between 0.0 and 1.0. The characteristic determinant is derived by the various boundary conditions and interface continuity conditions, and is solved directly by using Mullers' method, which computes the algebraic equation of high degree. The theoretical process of analysis and some numerical results represented by figures are given.

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The mechanical properties of epoxy resin are experimentally investigated under various curing temperature conditions using a rheometer of double cylinders. The properties are represented by a viscoelastic model of three elements and the values of the elements are determined on the basis of experimental results. The shrinkage of the resin is measured using dilatometer under various temperature conditions. The change of shrinkage over time is investigated. Internal stress under curing conditions is numerically calculated using the finite element method including experimentally determined material constants of the resin. The analysis is applied to a two-layered model composed of epoxy resin and aluminum alloy and a model of resin poured into a box. The deformation of the two-layered model under curing conditions is accurately predicted based on experimental results. The internal stress in the poured-resin model is influenced by the temperature of the resin. High curing temperature results in large internal stress.

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The stress and displacement fields for a viscoelastic medium with crack or rigid line inclusion are examined under in-plane and out-of-plane loads applied at infinity. The present analysis also gives sress intensity factors and stress singularity coefficients according to the time variations. The time-dependent behavior of the medium is assumed to be represented by the Burgers model of viscoelasticity for the cases of step-type loadings. Several numerical examples are given by graphical representations.

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Circumferentially notched cylindrical components of annealed copper were cyclically strained under diametral-displacement-controlled conditions. The localized cyclic stress-strain responses at several locations in the minimum cross section including notch roots were calculated by introducing the constitutive equation for analyzing cyclic hardening behavior, which was derived on the basis of dislocation dynamics in our earlier paper, into the finite-element method. The calculations showed that the mean stress and strain were generated on the minimum cross section under diametral-displacement-controlled conditions with displacement ratio R^D_e=-l.0, and a convex axial stress distribution produced in the first tensile stroke changed to a distribution exhibiting greater stress at the outer locatins in the minimum cross section as the cyclic hardening process progresses. Meanwhile, the axial strain and the equivalent stress and strain increased at locations farther from the center in the minimum cross section throughout the entire cyclic straining process.

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The present study is concerned with the formulation of a unified inelastic constitutive model describing the behavior of cyclic softening under temperature variations. For this purpose, we first examine the behavior of isotropic and kinematic hardening variables based on the results of cyclic experiments conducted by us under several constant temperatures and temperature variations. The results show that the cyclic softening is induced mainly by the kinematic hardening variables. The variation in the degree of cyclic softening with temperature variation is also discussed. Based on this information, the evolution equations of the kinematic hardening variables are formulated. By incorporating these equations into the unified model proposed previously by us, a final constitutive model is established. Monotonic, creep and cyclic tests under constant temperatures and temperature variations are simulated in order to evaluate the validity of the proposed model. The results show that the model can predict a wide range of inelastic behavior of this material with relatively high accuracy.

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Formulation of conservation laws of mass, momentum and energy for the region with moving interface between a solid and a liquid is described in the first part of the paper. Here, jump conditions of velocity, stress and heat flux on the interface are applied to give the fundamental equations including the Stefan condition relevant to the analysis of some problems incorporating melting/solidification. Discretized finite element equations for the analysis of temperature, stress/strain and melting/solidification in the course of welding are formulated using the thermo-elasto-viscoplastic constitutive equation.

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Fundamental and finite element equations developed in the previous paper by the present authors considering the effect of a moving interface between solid and liquid are applied to the simulation of the butt-welding process of plates with heat input from the electrode. Here, the analysis is carried out for half the cross section of the plate and the plane strain condition is assumed for stress analysis. The variations in the mode of deformation, velocity, temperature and stress fields are presented, where the emphasis is placed on the effect of the molten pool. The simulated results show that the proposed method is applicable to a practical welding process.

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The subloop behavior of TiNi shape memory alloy subjected to variations in strain and temperature was investigated experimentally through various kinds of loading-unloading and heating-cooling processes. The results are summarized as follows. (1) During the thermomechanical cycling, the martensitic transformation (MT) stress decreases but the MT temperature increases with increasing the number of cycles. In the case of variations in strain and temperature during the loading-unloading and heating-cooling processes, if strain is in the MT region, the MT stress and the MT temperature are almost constant not depending on strain. (2) If the material is used after the mechanical training of 20 cycles in practical applications, the MT stress and the MT temperature can be treated as almost constant.

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Numerical model for hot three-roll rolling is proposed, in which deformation of a material is analyzed by three-dimensional rigid plastic FEM, while temperature distribution in the material is calculated using a new combined method of three-dimensional FEM and one-dimensional FDM. First, the model is applied to simulation of the deformation and the temperature of the material in actual three-roll rolling processes, and calculated shape and surface temperature of the material are found to agree well with measured ones. Next, three-roll and two-roll caliber rolling processes in which round bars are produced from themselves after two passes are designed. Finally, calculated equivalent strain and temperature distributions of the material in the three-roll rolling process are compared with those in the two-roll caliber rolling process, and difference between the three-roll rolling and the two-roll caliber rolling is clarified.

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This paper deals with the numerical solution of singular integral equations of the body force method in the interaction problem of ellipsoidal cavities under uniaxial tension. The problem is solved by the superposition of two auxiliary loads : (i) biaxial tension and (ii) plane state of pure shear. These problems are formulated as a system of singular integral equations with Cauchy-type singularities, where the densities of body forces distributed in the γ, θand z directions are unknown functions. In order to satisfy the boundary conditions along the ellipsoidal boundaries, eight kinds of fundamental density functions proposed in our previous paper are applied. The present method is found to yield rapidly converging numerical results for stress distribution along the boundaries.

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A fundamental solution is presented in closed forms for axisymmetric problems of a transversely isotropic elastic solid subjected to axisymmetric body forces acting along a circle in radial, torsional and axial directions. In order to show the fundamental solution, we apply stress functions to transversely isotropic solids under axisymmetric deformation. As an example of applications of the fundamental solution, a solution is presented for the torsion problem of a transversely isotropic solid with a rigid spherical inclusion, Influences of elastic constants on stress distributions are shown by numerical calculations.

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This paper presents an analysis of constant temperature distributions in two co-focal elliptic boundaries of an isotropic elastic medium. The methodology is to use the complex stress functions φ and ψ, The complex function φ is found by solving the remaining boundary condition. φ is proposed in the form of a Laurent series with coefficients determined using a matrix representation. Using the analytic continuation through one of the boundaries, ψ is written in terms of the function φ. Several numerical results are given by graphical representation.

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The use of bellows expansion joints is an effective measure to rationalize various piping systems in industry. In the structural design, the requirements for prohibiting failures such as ratchetting, fatigue and buckling should be satisfied. The mechanisms of some failure modes of bellows are different from those of the ordinary vessels and piping components. It is a particularly unique characteristic that bellows buckle under internal pressure. The author has proposed an evaluation method for this failure mode in the elastic plastic region. However, in the case of high-temperature operation the creep buckling strength shound be considered. In this paper a simplified theoretical method for evaluating the critical time of creep buckling of bellows under constant internal pressure is proposed. In this method Norton's law is introduced to express material creep characteristics, and the meridional bending stress is assumed to be dominant.

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This paper is concerned with a compression in the case of different eccentricities at the upper and lower ends of carbon steel square pipes with a circular hole in a short column range, supported by a spherical seat. It was found that breaking of these carbon steel square pipes occurred local buckling of the eccentric flat wall with a circular hole. The buckling strength decreased as the eccentricity and open ratio increased. Consideration has been given to the formula and diagram which were obtained by combination of the analysis based on the energy method with the experimental result. The measurement results show that the formula and diagram yield in good design data, and are in good agreement with those obtained experimentally for a short column range.

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To investigate the deformation characteristics of a crystalline polymer, creep tests under tension, torsion and combination stress conditions were carried out after the cyclic prestrain of tension and unproportional circle using POM. It was shown that (1) after a tensional cyclic prestrain the deformation resistance of creep is decreased in the prestrain direction, and is increased in other directions; (2) after a cyclic circular prestrain, creep deformation resistance in combination stress direction (θ=45°) is increased, while creep deformation resistances in both directions of tension and torsion are decreased; and (3) strain course in successive creep How direction (θ=45°) is always developed along the load direction (θ=45°) in the cases with and without prestrain, independent of the prestrain history.

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The purpose of this study is to present an optimization method to create multiobjective structures by integrating shape optimization with topology optimization. The topology optimization method used here is based on the homogenization method proposed by Bendsoe and Kikuchi. As the shape optimization method, we used the traction method proposed by Azegami. By integrating these two methods, the optimal shape with smooth boundaries considering optimal topology can be obtained. A multiobjective mean compliance minimization problem of a linear elastic structure is formulated for both topology and shape optimization using the Lagrangian multipliers and the weighted Tchebycheff norm. The integrated optimization system is developed using a general-purpose FEM code to create multiply-connected Pareto optimal shapes. An application example of an automotive component in addition to a simple example is presented to confirm the validity and the practical utility of this integration method and the system.

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This paper deals with optimization of planar frames under a topological constraint to realize the frames in the form of a one-dimensional complex called "Tree". The tree has no loops and its number of connected components is one. In other words, its zero-dimensional homology group is isomorphic to an additive group of integers. and its one-dimensional homology group is equal to zero. The constraint consisting of the homology groups is satisfied by use of a generalized inverse matrix and the optimum structure is found by genetic algorithm. It will be possible to apply the method of treatment for the tree proposed in this paper to various meaningful topological constraints. Minimization of the total strain energy of tree frames is employed as a numerical example to verify the validity of the proposed method.

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The change in peak positions of a diffraction line with sin² ψ for various applied stresses σ_o was measured for determining residual stress of textured materials by X-ray diffraction. Three specimens were prepared from a sintered silicon carbide α-SiC and a cold-rolled stainless steel type SUS304. For each applied stress σ_o, seven peak positions for different ψ angles were measured. They were oscilated on the sin² ψ diagram. However, the slope M and the intercept N of the straight line that was fitted to the seven peak positions varied linearly with the applied stress σ_o. It is confirmed analytically and experimentally that this experimental evidence shows that the lattice strain for a fixed ψ angle varies linearly with applied stress as is the case with isotropic materials. Therefore, the stress constant K of textured materials can be determined experimentally as the reciprocal of the slope of the straight line of the M-σ_o diagram.

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A photoacoustic (PA) microscope with a quasi-open PA cell has been constructed to detect and visualize surface defects nondestructively. Two kinds of slit-type simulated cracks, cross-sectional views of which are a rectangle and a rectangle with quarter-circles at both ends, are fabricated artificially on an aluminum specimen. Imaging of vertical cracks with dimensions ranging up to several millimeters has been achieved using this apparatus. PA images of surface defects processed by a computer were shown with color graphics and cross-sectional views.

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