Fatigue strength and propagation characteristics of ceramic/metal joints were investigated under cyclic bending loading. Fracture surfaces were examined by SEM and X-ray methods. Fatigue fracture occurred at the metal/interlayer interface as well as the ceramic/interlayer interface. Fatigue strength was independent of the fracture path. Fatigue crack initiate and grow on the ceramic/interlayer interface at the specimen corner. Under constant amplitude cyclic loading, the fatigue crack decelerated and finally halted. As a result of the increasing amplitude of cyclic loading, the final fracture occurred at the metal/interlayer interface. Even under cyclic compressive loading, fatigue cracks were initiated on the ceramic/interlayer interface. This study looks at the method to evaluate the fracture mechanics parameter for interface cracks on ceramic/metal joints.

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Stresses around a crack in an interfacial layer between two dissimilar elastic half-planes are obtained. The material constants of the layer vary continuously within a range from those of the upper half-plane to those of the lower half-plane. An internal gas pressure is applied to the surfaces of the crack. To solve the problem, the interfacial layer is divided into several layers with different material properties. The boundary conditions are reduced to dual integral equations. The equations are solved by expanding the differences of the crack faces in a series. The unknown coefficients are determined using the Schmidt method. Numerical calculations are carried out for some crack configurations.

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A new method is presented for stress intensity factor analysis of interface crack problems under thermal stress conditions. The virtual crack extension method, which is used with the finite element method, is a powerful tool for estimation of the energy release rate. The virtual crack extension method is applied to stress intensity factor analyses of thermal interface crack problems. The energy release rate obtained by the virtual crack extension method is separated into individual stress intensity factors, K₁ and K_II, by the principle of superposition. The presented method is applied to several thermal stress interface crack problems. The results are compared with those obtained by the displacement and stress interpolation methods. It is found from these analyses that the present method gives very accurate results which are insensitive to the size of finite elements.

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Moire interferometry was utilized to determine the displacement fields around a crack tip in single-edge-cracked tensile PMMA and PA6/PPE/SBS alloy specimens. Vertical displacement ν was expressed as a function of the distance γ and the angle θ from a crack tip, and compared with the approximate solution of linear elastic fracture mechanics to study its applicability to polymers. The results showed that the solution agreed with the experimental results for the vicinity of a crack tip in the PMMA specimen. For the alloy specimen, however, the solution gave much smaller values than the experiments. The principle of superposition was employed for determining the values of ν (=ν-ν'), i.e. the difference between two displacements ν and ν' which was related to a uniform strain field without a crack. The expression for ν was also introduced to analyze the effects of γ and θ. It was found that ν was an important factor in increasing ν values near the crack tip, and the ν expression well represented the effects of γ and θ for both the PMMA and alloy specimens.

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The fracture behavior of high strength steel under the influence of hydrogen was studied, with an emphasis on the conditions for the formation of intergranular (IG) cracks. Mechanical tests were carried out using two types of high strength steels (Series A and B) which had been heat-treated to obtain the same level of yield stress bus different grain boundary properties. The specimens were cathodically charged with hydrogen under constant stress conditions. Experimental analyses revealed that a high stress concentration at a fatigue pre-crack tip is required for generation of IG cracks. The morphologies of the fracture surfaces were intergranular (IG) and transgranular (TG) modes, respectively, in the two types of specimen, and the differences in morphology were found to result from differences in the amount of impurities segregated at the grain boundaries of the specimens.

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Rotating bending fatigue tests were carried out for Inconel 718 at room temperature to investigate the growth characteristics of a small crack. It was found that : (1) The crack initiated at the grain boundary and then propagated as a transgranular crack. (2) When the stress level was higher than the fatigue limit, the fatigue life was mainly controlled by the growth life of a crack smaller than 1mm. (3) The fatigue limit was a limiting stress for the crack propagation. (4) At low stress levels (σ_a/σ_0.2<0.5, σ_a : stress amplitude, σ_0.2 : 0.2% proof stress), the crack growth rate was determined by the stress intensity factor range ΔK ; and at high stress levels (σ_a/σ_0.2>0.6), it was determined by the small crack growth law.

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A through-thickness center-cracked specimen of fully annealed copper was cyclically deformed under a load-controlled condition. Then cyclic stress-strain response in the vicinity of the crack tip and the crack tip opening displacement were calculated using the elastic-plastic finite element method in which the constitutive equation derived on the basis of dislocation dynamics is used. The distributions of the axial and shear strains along with changes in them and in the crack tip opening displacement during each half of a load cycle were calculated ; the results corresponded well with the measurements. In addition, the calculated stress-strain response showed that the axial strain range and the mean strain decreased to a much greater extent closer to the crack tip as the cyclic loading process progressed.

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An impact fracture test was performed on S 45 C near the transition temperature. The impact fracture test showed that a brittle fracture was always accompanied by a preceding ductile crack. The generation of the ductile crack occupied the majority of the absorbed energy in the impact test. Therefore, the generation of a ductile crack by an other pre-loading process was considered to be harmful for the impact strength. In this report, tests were performed to investigate the effects of preloading such as pre-impact, large straining and low cycle fatigue on the absorbed energy. Test results showed that a ductile crack deeper than 0.15 mm generated by pre loading substantially reduced the absorbed energy.

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The static fatigue strength and fracture mechanism of ceramic/metal (Si₃N₄/Cu/SUS304) joints were investigated under a four point bending loading. The results clearly showed characteristic of static fatigue. The static fatigue strength at 30 days was about 65% of the static bending strength. Fracture surfaces were examined by SEM and EPMA after the static fatigue test. On the basis of these results, it was determined that the fracture mechanism of the static fatigue test is the same as that of the static bending test. The crack initiates and grows at the ceramic/brazing metal interface and finally kinks to the ceramic side. The crack initiation stress was successfully detected using the AE technique. It is shown that the crack initiates during loading and the time-dependent crack growth occurs under sustained constant load.

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The fracture mechanisms of a creep-damaged Class A SMC composite with notch are investigated by the acoustic emission (AE) technique and the residual strength is estimated. The creepdamage mode is mainly the fiber or the filler debonding, but fiber breaking appears in the case of high temperature and long loading time. The residual strength can be represented by the ratio P/P_(N) of loads, showing a change in the damage mechanisms of a creep-loaded specimen and a non-creep loaded specimen_(N). It is found that the residual strength decreases remarkably with long creep loading time when the temperature is higher than 150°C.

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An apparatus for measurement of the dynamic displacement of a subject has been constructed. It consists of a position sensing detector (PSD), optical fiber and He-Ne laser light source. One end of the fiber is coupled with the light source and the other end is mounted on the moving subject. The laser light from this fiber end on the subject is focused on the PSD which is used to evaluate the change in the subject displacement. The characteristic frequency response of the apparatus has been studied in detail and is concluded to be as high as 100 kIlz. The apparatus was used in an impulsive three-point bend test for notched PC specimens and showed excellent serviceability for impact studies.

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It is well known that the K_IC test for determining static strength is not only very complicated compared with the tensile test but also very sensitive to specimen dimensions. For this reason the J_IC test, which is not easy to perform, is often used thus it is desirable to establish a simple method for evaluating fracture toughness. In this study, we investigated the fracture toughness test by the unloading compliance method, and proved a method for estimating of fracture toughness by utilizing the tensile properties of metallic materials. In both methods, we used six kinds of steel, one titanium alloy and three aluminium alloys turned in the optional rolling direction (L-T, T-L). The following relation was observed between plane strain fracture toughness K_IC and the uniaxial tensile properties obtained from JIS14A tensile specimens in rolled steels and non-ferrous metals. K_IC=0.178[numerical formula]-4.0 (E : Young's modulus. σ_r : True fracture stress, ε_f : Fracture strain). It is possible to evaluate K_IC within an estimated error of ±7%.

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We consider the cryogenic fracture behavior of an elastic-plastic material and the energy dissipation associated with crack extension. The results of a fracture toughness test are presented for a forged JJ1 type austenitic stainless steel plate at liquid helium temperature. Temperatures of a compact tension specimen were also measured during straining at 4 K. A two-dimensional finite element analysis was used to interpret the experimental measurements. The elastic-plastic fracture behavior was analyzed using the Dugdale model and the incremental strain theory. In the calculations the material was assumed to be elastic-prefectly plastic and to obey the von Mises criterion with its associated flow rule. The dissipated energy can be calculated from the change in total elastic strain energy of the specimen during crack extension. From the calculated dissipated energy, the associated temperature field near the crack tip was predicted and compared with the measured values. Generally good agreement was found between the computed and the measured values.

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In the present paper, the nonlinear Berger equation for large deflection problems of plates and the finite difference method are utilized to obtain solutions for deformation in doubly-connected plates on an elastic foundation. The analysis is carried out for a rectangular isotropic plate with a rectangular rigid body at the center. Numerical solutions are presented in order to illustrate the influence of the rigid body size on the maximum deflection in uniformly loaded plates on an elastic foundation. The numerical procedure is easier than other procedures, such as the finite element method, and reasonable results are obtained.

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The exact transient closed-form solutions for a suddenly applied dislocation, such as a crack or fault which travels at a constant velocity and depth below the surface of an elastic half plane, are obtained in this study. First, the transformed solution of Navier's equation in the Laplace and Fourier domain are obtained, then the inverse transforms are carried out using the Cagniard-deHoop method to obtain the closed-form solution. The numerical results of the stress and velocity fields are shown for the cases of subsonic and supersonic traveling velocities. In the subsonic case, responses differ according to the traveling velocity such that the responses at a point along the moving direction are larger than the results of the leaving direction. In the supersonic case, impact waves occur and reach the surface before the primary wave.

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Nonlocal elastic constants have been related to atomistic properties elucidated by atomic simulation through a macro-micro linking approach proposed in a previous paper (Trans. of JSME, Vol. 62, No. 601, 1996, 2054-2059). These nonlocal properties are evaluated either for the initial relaxed (metastable) structures of condensed matter or for structures under infinitesimal deformation. Therefore they could be called intrinsic (elastic) nonlocal properties. They appear tiny for the conventional cubic lattice structure like a face-centered cubic lattice (fcc), as predicted in the 1960s. In this second report, nonlocal material constants such as characteristic length are estimated for both homogeneous centrosymmetric bulk lattice structures and inhomogeous relaxed surfaces and grain boundaries. Some surfaces with a low-to-high index and consistent tilt grain boundaries are constructed using molecular statics or molecular dynamics simulations employing the many-body potential. The nonlocal properties extracted from these atomic configurations are found to be sensitive to inhomogeneity, while the characteristic length itself is less than one-fifth of the lattice parameter.

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In this paper, a new method is suggested for the nondentructive measurement of elastic moduli on the local surface of an anisotropic material by an amplitude-and-phase-measuring acoustic microscope. It is confirmed that the anisotropic wave velocities in a local area are determined from the complex V (z) curve measured by a line-focus acoustic lens. The experimental analyses were carried out for single crystal of cubic system, GaAs (001), with water or mercury as the coupler. The velocity of the surface wave was clearly seen when the acoustic impedance of the coupler was smaller than that of the specimen. The velocity of the longitudinal wave was successfully measured, provided the acoustic impedance of the coupler was comparable to that of the specimen. Then, the elastic moduli in a single crystal of GaAs was determined from the measured longitudinal and surface wave velocities according to elastodynamic theory. It was shown that the present method is very useful in determining the anisotropic elastic moduli of a cubic system in a local area.

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By using the X-Z mode operation of a Scanning acoustic microscope (SAM), the velocity of waves propagating on a specimen can be determined. The waves propagating between solid and liquid are influenced by the density ratio of the solid and liquid. In order to undersand the meaning of the measured results obtained using SAM, theoretical analysis of wave propagation was carried out considering the weight density and acoustic velocity of water. The relations of density ratio and velocity of waves propagating on the boundary between a solid and liquid were obtained.

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Etching properties of INCONEL718 with various degrees of fatigue damage have been investigated. The etching properties have been found to be sensitive to low-cycle fatigue damage given to the meterial. Low-cycle fatigue damage was simulated using load-controlled uniaxial fatigue tests at 600°C and also at room temperature, and samples with various degrees of fatigue damage were prepared. A chemical etching technique was utilized to detect fatigue damage, and it was found that the etching method preferentially etches persistent slip bands (PSBs) in the fatigue-damaged materials. The density of slip bands increased with increased fatigue life fraction and showed an unique correlation with a usage factor N/Nf. In conclusion, an applicability of the etching technique to fatigue damage evaluation has been suggested.

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Stress dependence of magnetostriction was utilized to measure the residual stress in butt welded steel plates. The magnetization of steels starts with the domain realignment, which is followed by the rotation of the domain magnetization. The magnetostriction increases while the domain realignment is dominant and then decreases showing a maximum value when the rotation magnetization starts to occur. The maximum magnetostriction depends on the stress level and the relationship between the stress axis and the magnetization direction. In this study, the maximum magnetostriction was measured while applying uniaxial stress to the steel specimens. We found that the maximum decreases when the magnetization direction is parallel to the tensile stress or parallel to the compressive stress and that it increases when magnetized normal to the tensile stress or parallel to the compressive stress. The results were then used as master curves to nondestructively measure the residual stress in butt welded steel plates. The predicted stresses showed good agreement with the strain gauges.

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Creep properties in a sheet of shape memory polymer of polyurethane series at low temperature below the glass transition temperature were investigated experimentally. The results are summarized as follows. (1) Creep strain in the early period is expressed as a logarithmic function of time. Thereafter, creep strain saturates to a certain value. (2) In order to keep the creep strain smaller than 10% for 1000 hours. it is necessary to maintain a stress lower than 20% of the yield stress. (3) Although creep strain remains after unloading, it is recovered by heating. The strain recovered by heating is about 50% of the residual creep strain.

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Laser surface acoustic waves (SAW) were utilized to detect the artificial subsurface lateral delamination in Unidirectional (UD)-GFRP. The amplitude distribution of the Rayleigh and Lamb waves over the surface was obtained by the wavelet transform of the SAW monitored by a heterodyne-type laser interferometer and was successfully utilized to detect the subsurface delamination area. The depth of delamination was accurately estimated by analysis of the phase velocity dispersion of the SAW.

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Instrumented dropweight impact tests are conducted for CFRP laminates. Impact-induced damage, transverse cracks and delamination are investigated microscopically. Transverse crack density and delamination area are measured as functions of impact energy. In addition, the residual compressive strength is measured, and the correlation between the impact energy and the microscopic damage with the attributed residual compressive strength is discussed. It is found that the residual compressive strength decreases as the impact energy increases but above a certain impact energy, the decrease in the strength becomes gradual.

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The effects of stress on the Raman frequencies of crystalline silicon are studied using molecular dynamics simulation, both for uniaxial stress along the [100] direction and for biaxial stress which is isotropic in the (001) plane. The Tersoff potential is used to represent the interaction among the silicon atoms. Simulation results showed that the stress causes the Raman frequencies to shift. The phenomenological coefficients which are needed to calculate the stress from the shifts of the Raman frequencies were obtained by comparing the simulation results with the dynamical equations for optical modes. The values obtained for the coefficients agreed well with the experimental values obtained by Chandrasekhar et al. [Phys. Rev., B17. (1978), 1623]. The obtained relationship between the uniaxial stress and the Raman frequency for vibration in the [001] direction also agreed well with the experimental result we obtained using microscopic Raman spectroscopy.

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In the shape optimization of a large-scale problem, the shape design sensitivities for many distinct parameters must be calculated after successive shape modification. In order to improve the computational efficiency of the analysis, we present the implementation of Trefftz-type sensitivity analysis scheme to a cluster computing system. The present scheme is applied to a two-dimensional potential problem in order to confirm its validity.

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A method of elastic analysis is studied for double walled corrugated fiberboard (DWCF) of symmetrical shape (to the machine direction) under uniform bending of the moment axis perpendicular to the machine direction. Then this method is applied to stress analyses for several shapes of DWCF. The following results are obtained. (1) Deformations of kraftliner (KL) and corrugated medium (CM) in DWCF under the uniform bending are expressed as the sum of simple tensioncompression and uniform bending. (2) Maximum stresses σ_klmax and σ_slmax for KL and CM on the upper side are equal to σ_klmax and σ_slmax on the lower side. σ_klmax is on the outer surface, and σ_slmax is at the KL (middle KL)·CM joint on the inner surface. (3) σ_slmax increases with the increase of the wavelength and the thickness, and decreases with the increase of the height for CM.

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Stress distributions in a canine left ventricular wall are simulated during one cardiac cycle by employing 3-dimensional finite element models developed in order to estimate the functions of the left ventricle. The appropriateness of the numerical simulator is examined by comparing the pressure volume relationships of the left ventricle computed by the present system with those obtained by the corresponding canine experiments. The initial geometry of the left ventricle is assumed to be a prolate spheroid in order to facilitate easy estimation of the complex computed numerical results. It is recognized that the distributions of the wall stress, e.g., the circumferential stress, near the equatorial surface are quite different from those of the thick cylinder subjected to the internal pressure and that the magnitudes and the directions of the principal stresses are closely related to both the contractility and the orientation of the myocardial muscle fiber.

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The dynamic and static stress-strain curves of steels (SCM3, SUJ2, S55C, SK3) hardened by heat treatment from HV360 to HV820 were determined by means of a three-point bending test under various strain rates. For convenience, an instrumented Charpy impact bending was used at high strain rates, and a previously proposed constitutive equation was applied to these curves. Results agreed well with the experimental values and their applicability to hard steels was shown. The experimental constants included in the equation for the present materials were closely concerned with the hardness. Therefore, the calculated curves of the stress-strain rate relation at a given strain using constants expressed by the hardness were compared with the experimental ones and showed good agreement.

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Analyses of cylindrically anisotropic elastic bodies with circular opening or circular ring reinforcement have been performed for cases of in-plane loading at infinity. We present the closedform stress and displacement solutions for circular hollow or solid inclusion in a cylindrically anisotropic elastic medium with a shear sliding boundary at the interface under out-of-plane shear and in-plane loadings at infinity. Several numerical results are graphically represented.

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This paper presents a 3-dimensional finite-element numerical analysis of shear banding using the internal time theory of viscoplasticity together with the derivation of the differential stress-strain relationship. The employed constitutive equation includes both isotropic and kinematic hardening laws. The softening effects are also included in the constitutive equation in order to produce shear banding. The effect of the deformation velocity and the employed hardening laws through 3-dimensional analysis in comparison with that of 2-dimensional cases is discussed.

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The published theory of plasticity in soil is established in such a framework that the hardening modulus h vanishes when the volumetric compressive strain rate ε_p is zero. In general, soil shows dilatancy under relatively low pressure, where h is negative. This is called strain softening. On the other hand, it is proved theoretically that plastic instability arises at h=0. However, at ε_p&le;0 plastic instability has not been generally observed in reality. We have developed a modified theory of plasticity in soil where the hardening properties of soil are made consistent with the expanding characteristics of the yield surface. As a result, the phenomenon of strain softening is eliminated in the theory. The velocity gradient is discontinuous on the necking plane forming a boundary between the shear band and its exteriors. On the other hand, a characteristic plane is the one beyond which solutions cannot be extended without additional information, because some of the derivatives normal to the plane cannot be determined using their governing equations alone. Therefore, on the characteristic plane, some derivatives of stress rates become indefinite and such a property must also be required for the necking plane. We examine the mode of the characteristic plane in a simple cap model. There are two modes, P and O. Mode O corresponds to the shear band mode arising in a plane strain compression test. Good agreement is obtained between the theory and the experiment by Vardoulakis when taking about 40 degree as the inclination angle in the Mohr-Coulomb criterion.

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This study deals with adaptive meshes for boundary element analysis with a nonlinear mixed boundary condition such as heat radiation. A local iteration scheme is used to solve the nonlinear equation system arising from the nonlinear boundary condition. Local reanalysis, which measures approximately the sensitivity of the boundary element solution to local mesh changes, is employed for error estimation. The L₁-norm is used to measure both local and global errors. To test the applicability of the proposed scheme, an h-version mesh refinement strategy is described and applied to two-dimensional potential problems.

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A combined model of FEM and BEM is proposed and formulated for plane stress problems using the same concept in the rigid-body spring model (RBSM). The proposed simple bond elements are applied to the problem of uniaxial tension of a rectangular plate with a circular hole which contains a circular disk with the same initial diameter as the hole. The plate is divided into boundary elements in the BEM and the disk into finite elements in the FEM. The simple bond elements are introduced into the plate-disk interface. The normal stresses on the contact arcs are compared with those determined using an exact elastic analysis and the FEM. The combined model proposed here is found to be effective for contact problems. The contact problem of a cantilever with a built-in wall is also analyzed by this method, and the elasto plastic behavior of the cantilever is analyzed.

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A new plug welding process (called hybrid-spot welding) was proposed for thick plate welding. A boss and a hole were produced in each base plate by press forming for the positioning of both plates. The boss of the lower plate was set into the plughole. The plug welding was then carried out. In this paper, the shear fracture behavior of the hybrid-spot welded joints was investigated under tensile loading both analytically and experimentally. In this welding, the strength of the joints could be evaluated from the shear strength of the boss since the melt pool did not reach the lower plate.

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Pin joint strength of laminate type C/C composites was experimentally determined as functions of the diameter and position of the pin hole. Three types of laminate, (0°/90°), (±45°), and (0°/90°/±45°) were examined. It was found from the comparison between predicted and observed stress distributions that the effect of stress concentration around the pin hole on the pin joint strength was quite low for the C/C joint, when tensile or shear modes of failure appeared. On the other hand for the case of compressive failure maximum stress criterion can be adapted except for the ±45°laminate. By use of these fracture criteria, a design procedure of C/C pin joint is proposed and it is demonstrated that the pin joint strength of C/C composites can be precisely predicted based on tensile, compressive and shearing strength of smooth specimen.

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The fatigue life estimation of solder joints is one of the most critical requirements in the development of reliable electronic components. Since the electronic components are subject to temperature variations under field conditions with a trapezoidal wave, it is important to obtain quantitative knowledge regarding the effects of hold-time on fatigue life. In this study, we first carried out low cycle fatigue tests using thin-walled cylindrical specimens. The specimens were subjected to strain controlled loading conditions with a trapezoidal wave and a variable strain rate wave in consideration of stress relaxation and elastic follow-up phenomena. It was confirmed that the fatigue life of the 63Sn-37Pb solder can be uniformly evaluated using an inelastic strain range and Coffin-Manson equations when the strain rate is low. Second, elastic-creep stress analysis was carried out for solder joints in a TSOP (thin small outline package). It was shown that the increase in creep strain during hold-time has a noticeable effect on the fatigue life under field conditions. Thus, careful consideration of creep deformation is essential, and consequently stress analysis based on the elastic-creep model can serve as a fatigue life estimation method in the reliability design.

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