Creep-fatigue tests were conducted with Modified 9Cr-1 Mo steel at 600°C in a very high vacuum of 0. 1 μPa in order to observe "pure" creep-fatigue behavior free from environmental effects. On the whole, time-dependent life reduction occurs when duration of tension is longer than duration of compression. A good correlation was observed between creep-fatigue life and fracture mode. When the fracture mode is transgranular, no time-dependent life reduction occurs. In contrast, when it is predominantly intergranular, a significant life reduction is observed. The overstress was experimentally analyzed to evaluate the creep-fatigue damage. The relationship between the overstress and the inelastic strain rate can be fitted with a bilinear curve independent of the strain range. At a lower strain rate, the line has a gradient ; however, there is no gradient at a higher strain rate.

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The stress field near a corner of jointed dissimilar materials under antiplane shear has singularities. If G₂ > G₁, there exists only a singularity of the symmetric type. In that case, the stress singularity is λ₁ -1 and the singular stress fields near a corner of jointed dissimilar materials are described in terms of a pair of constants λ₁, K_{III, λ1}. If G₂< G₁, there exists only a singularity of the skew-symmetric type. In that case, the stress singularity is λ₂-1 and the singular stress fields must be described in terms of a pair of constants λ₂, K_{III, λ2}. The parameters K_{III, λ1}, K_{III, λ2} are determined using numerical analysis. In this study, K_{III, λ1}, K_{III, λ2} in the model of an infinite plate with lozenge inclusion under antiplane shear are calculated through the body force method.

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In addition to uniaxial tension and through-thickness compression reported in the previous paper, commercial-purity aluminium and deep-drawing-quality steel sheets are tested in plane-strain compression and simple shear. The yield loci and the equivalent stress-strain flow curves based on Hill's 1948 quadratic, Hil1's 1990 nonquadratic and Gotoh's biquadratic criteria are obtained on the basis of equal amounts of plastic work. The yield loci calculated from Hill's quadratic criterion for case (2) in which the anisotropic parameters are mainly determined with yield stresses and Gotoh's biquadratic criterion are close to each other and provide fairly good fits to the experiments except for the annealed aluminium. Hill's theories for case (2) are also found to be rather reasonable for all the materials used here when the flow curves are compared with each other.

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Tensile tests of S45C/Si₃N₄/S45C bar-type specimens, which were bonded in 1987 and 1988 by the metalizing method, were carried out t room temperature in laboratory air. Then, bonding-induced tensile residual stress was mesured at the surface of Si₃N₄, near the boundary by means of the X-ray diffraction method. Generally, the crack initiated at the boundary between S45C and Si₃N₄, and then propagated into Si₃N₄. In this case, the fracture stress decreased with increasing diameter of the specimen, but the tensile residual stress increased (with increasing diameter of the specimen). In spite of the same diameter, the fracture stress of the specimen bonded in 1988 was lower than that bonded in 1987 and the tensile residual stress was larger. A good correlation was recognized between the fracture stress and the bonded-induced tensile residual stress. Consequently, it is concluded bonding-induced tensile residual stress is one of the important factors for fracture stress in ceramic/metal joints.

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The deformation behavior of aluminum single crystals (99.998% purity) was investigated using a compression test at room temperature. Static tests (1×10^-5∼1×10^-1 s^-1) were performed with an Instron machine, and dynamic tests were performed using a Hopkinson pressure bar system. The flow stress of a crystal properly oriented for double slip increases with increasing strain rate in the range of 1×10^-5 to 1×10^-1 s^-1, while that of crystals properly oriented for single slip is independent of strain rate in the same range. Flow stress increases rapidly with increasing strain rate beyond 4×10² s^-1 for all crystals. From observation with a scanning electron microscope, it is revealed that as the strain increase, the density of slip bands increases and the contrast of slip bands is weakened.

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Residual stress in the silicon substrate after local thermal oxidation was investigated experimentally and analytically. Shallow trenches about 0.3 μm deep were formed before 1000°C oxidation. Residual stress in the substrate after the oxidation was measured using microscopic Raman spectroscopy. Tensile stress of about 50 MPa initially occurred at the substrate surface. However, the residual stress decreased with increasing thermal oxide film thickness, and then compressive stress increased. The stress development mechanism was analyzed using a finite element method. There were three main mechanisms, oxidation-induced stress at the curved surface, deflection of the nitride film which was used as an oxidation protection mask, and constraint of free volume expansion of the newly oxidized film. The predicted stress change with increasing oxide film thickness agreed well with the measured results.

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Transient interfacial stress between two bonded dissimilar anisotropic media to an impulsive line SH-source is considered. The principal axes of each anisotropic medium do not coincide with the line on the plane of the bonded interface. Applying the well-known Cagniard's technique, an exact closed form solution for the transient interfacial stress is derived. It is shown that the distribution of the interfacial stress is affected more by the off-angle in the source side medium than by that in the transmitted one.

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This paper discusses the stress concentration problem of a bonded elastic solid with an ellipsoidal elastic inclusion in the bonded layer under torsion. A method of solution is developed for the problem mentioned above using a fundamental solution for torsion problems of a bonded elastic solid with a bonded layer. Influence of the shape of the ellipsoidal inclusion on the stress distribution around the inclusion and on the bonded plane is investigated. Influence of the share moduli of elasticity on the stress distribution is also shown.

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It is generally known that Lagrange's classical plate theory is not appropriate for large deflection problems. However, there are very few reports which investigate the range of applicability of the classical theory by 3-dimensional finite deformation elastic solution. Therefore, in this paper a uniformly loaded circular plate with a clamped edge is analyzed using 3-dimensional finite deformation theory, and by the use of these results, the applicability of Lagrange's theory is examined. As a numerical method, the 3-dimensional finite element method which is formulated using the incremental theory based on the convected coordinates is used.

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Energy reflection of plane elastic waves impinging on an inhomogeneous elastic layer is investigated. The variation of acoustic impedance throughout the inhomogeneous layer is given as a linear function of thickness coordinate of the layer. Closed-form analytical solutions of the coefficient of energy reflection and transmission are obtained for the normal case to show fundamental but reliable results. The discontinuity of acoustic impedance at interfaces dominantly affects energy reflection. The effect is systematically explained from the variation in impedance. The special coefficients for the long wave limit coincide with the well-known results for a homogeneous elastic layer. The model presented here may be applicable to such materials as a transitional layer of deteriorated bonding interface or a layer of functionally gradient material.

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When performing a photoelastic stress analysis around a stress singularity, such as a concentrated loading point or a crack tip, accurate results of stress analysis usually cannot be expected because of a collapsed image of the fringe due to a steep variation of stress and the insufficient resolving power of ordinary equipments. The function approximation method is a successful and convenient method for compensation of collapsed photoelastic isochromatic data in an extremely condensed area, which has been developed based on a concept of hybrid theoretical and experimental stress analysis. In this study, we determined the opening mode stress intensity factor using the function approximation method in a photoelastic experiment within 3 percent relative error against the theoretical value. The isochromatic image data around a stress singular point were reconstructed.

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Torsional fatigue tests of ferritic spheroidal graphite cast iron were carried out and the fatigue processes were investigated through successive observations using the plastic replica method. The effects of overstress on the behavior of microcracks when a few cycles of overstress are applied intermittently (every 10⁷ cycles) during the repetitions of understress to the specimen were discussed. The main results obtained are as follows : (1) The fatigue limit is determined by the limiting condition for the propagation of a Mode I microcrack. (2) When a few cycles of overstress are applied intermittently (every 10⁷ cycles) during the repetitions of understress, the specimens can be broken even when the accumulated cycle ratio Σ(n/N) is much smaller than 1. (3) The effect of overstress on the fatigue behavior during understress cycling is larger in ferritic spheroidal graphite cast iron than in plain carbon steel.

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A statistical method for lifetime prediction is important for determination of the fatigue behavior of ceramics, because the lifetime data of ceramic materials are scattered. In this study, the lifetime data of silicon nitride ceramics were obtained using piezo bimorph fatigue equipment with stress ratio R =0.1 and frequency f=150 Hz (sine wave) . A statistical method for estimating the relationship between the initial applied stress intensity factor (K_Imax) and the fatigue lifetime (N_f) was proposed. By this method, a single K_{Imax-Nf diagram was obtained even if the maximum applied stress levels had been different in cyclic fatigue testing. It was proved that the distribution of the fatigue lifetime was determined by the distribution of initial cracks. The crack growth rate (KI-V) diagram was estimated using Fett's method from the K<Imax}-N_f diagram. Acceleration of the crack growth rate in natural cracks was observed in the region of lower applied stress intensities.

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Previously, Isida analysed a row of equal cracks distributed with equal spacings subjected to tension, in-plane shear, longitudinal shear and classical bending. In all the problems, the stress intensity factors were found to be nearly linear with 1/N for fixed values of λ, where N and λ are the number of cracks and the length-spacing ratio, respectively. In this paper, the relationships between the stress intensity factors and N are given in a more refined manner with theoretical proofs. They apply not only to cracks, but also to holes and inclusions of arbitrary shapes. Based on these relationships, reliable formulae of the stress intensity factors are proposed for collinear and parallel cracks under various loads.

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In this paper, a new method of analysis is proposed for an infinite solid containing an embedded plane crack of arbitrary shape. The analysis is fundamentally based on the body force method, but proper expressions of the body force densities are introduced and the stress conditions of the crack surface are replaced by the resultant force conditions in order to improve the accuracy and validity. Numerical results for typical crack problems based on coarse mesh patterns are shown to be in good agreement with the known solutions. The method is also applied to the bending problem of circular and rectangular cracks regarding the surface contact on the compression side, the reliable solutions of which have been unattainable using the previous methods. The obtained results are found to be very different from the conventional free surface solutions.

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In this paper, a new versatile method for analizing a semi-infinite body with an arbitrary surface or internal crack under complex loading conditions was proposed. New numerical results were obtained in many cases, and compared with the other solutions. As a result, it was found that the present method is very powerful and gives highly accurate results with no extrapolation procedures even in the case of coarse meshes.

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The reopening behavior of a transverse crack which is induced on the surface of a borehole by hydraulic fracturing is analyzed to establish the methodology for hydraulic fracturing tectonic stress measurements, where, as a typical transverse crack, a penny-shaped crack which is induced perpendicularly to the borehole axis is considered. To this end, a model is constructed for analyzing the coupled problem of fluid flow in the crack and crack reopening behavior in an impermeable rock. The model takes into account the fact that the crack does not reclose perfectly upon deflation due to crack surface damage and minor shear displacement. The results show that the apparent reopening pressure, i.e., borehole pressure at which the pressure-time history clearly deviates from linearity, decreases and approaches the compressive tectonic stress normal to the crack plane with decreasing injection flow rate, and that it is almost proportional to the compressive tectonic stress independently of injection flow rate.

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Since the critical size of defects in ceramics is normally very small, the conventional method of fracture mechanics often becomes inappropriate. In the present paper, the fracture strength of silicon nitride with small defects is evaluated based on the R-curve method. Parameters of the R-curve of silicon nitride are determined from the experimental relationship between the fracture strength and the defect size. For penny-shaped cracks, the fracture strength is constant for small defects and the critical stress intensity factor is constant for large defects. The equivalent defect size is an excellent parameter for correlating the fracture strength with the size of elliptical cracks with an aspect ratio between 0.3 and 1. For small voids, the fracture strength is nearly the same as that for a penny-shaped crack. On the other hand, for large voids, it approaches a constant value which is equal to the strength of materials without voids divided by the elastic stress concentration factor. When the tip radius of long deep notches is small, the critical stress intensity factor for the fracture is independent of the tip radius. A Monte-Carlo simulation of bending fracture of silicon nitride was performed by random distribution of penny-shaped cracks with random sizes in a specimen by a computer. On the basis of twenty five runs of fracture simulation, the relationship between the bending strength and the defect size, and the cumulative distribution function of the fracture strength were successfully derived.

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In the present study, impact fracture patterns of plates subjected to an impulsive load are investigated by means of experiments and numerical simulations. The center of the free edge of a rectangular plate with uniform thickness is subjected to an impulsive load in the in-plane direction while the opposite edge and both side edges are free from stress. The impact fracture experiments are performed with plaster plates of several dimensions and length-width ratios. The features of fracture patterns which occurred in the plates are discussed. Numerical analyses for several fracture patterns are carried out based on a dynamic finite element method using the Newmark-β method. It is made clear that the origin of the fractures mainly corresponds to the regions of dynamic tensile stress concentration due to stress wave reflection and reinforcement from the back edge and both sides of the plate.

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The fracture mechanisms of Class A-SMC (Sheet mould compound) composites with various contents of fiber and filler are studied by means of the acoustic emission monitoring. It is found that the loads of P_b and R_c at the inflection points of the total AE energy curve determined by means of the energy gradient method are in good agreement with the loads determined by means of the stress intensity factor method. The loads increase with an increase in the fiber content and show values near or equal to the maximum at 160 phr of the filler content. The damage of constituents at the loads are deduced from the AE amplitude distribution and the frequency analysis. The effects of the fiber and filler contents on damage initiation and growth are confirmed on the notch tip at the loads by means of the ink staining method.

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This paper discusses the tensile properties and acoustic emission behavior of Ni-NiO alloys and Ni-Al₂O₃ alloys prepared by means of the PM method. The mechanical properties of these materials were changed by their manufacturing process conditions. In the case of Ni-NiO alloys, the sintering time of 3.6ks along with repressing and resintering processes may be effective. On the other hand, the best conditions for Ni-Al₂O₃ alloys are the sintering time of 10. 7ks with neither repressing nor resintering. The AE characteristics of Ni-NiO alloys became highly apparent. It appeared that the AE events generated in the region of 5-40% strain were related to the decohesion of the matrix / dispersoid interface. The AE events with high energy and high peak amplitude before fracture of the Ni-NiO specimen were produced by intergranular cracking. The AE activity of Ni-Al₂O₃ alloys was weaker than that of Ni-NiO alloys ; that is, the peak amplitude distribution of AE events generated in Ni-Al₂O₃ alloys became narrow and most AE events had low energy.

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Finite element simulation was carried out for inhomogeneous elastic-plastic fracture specimens, which consist of A533B steel and HT80 steel. These two materials have considerably different yield stresses, although their elastic properties are exactly the same. The nonlinear fracture parameter, T^* integral, was extended for inhomogeneous multilayer materials. The T^* integral for inhomogeneous materials demonstrates excellent path independence, even in the stages of large plastic deformations around the crack tip and the material interface. Numerically generated moire fringe patterns are in good agreement with experimentally recorded patterns. The shapes of plastic zones appearing in the specimens reveal large inhomogeneity effects.

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Our previous paper reported that a theory presented on the basis of Hertz contact and sliding between spheres agreed well with experiments for the force-displacement relation (P<2000N) of a packing body. In this paper, the experimental results for the force-displacement relation over a large range of force, radius of spheres and depth of packing body are presented and compared with the theory proposed in the previous paper. The deformations of the packing body are limited to an elastic region and the case of loading process. As a result, it is shown that the experimental values of force are larger than the theoretical value for forces above 2000 N and larger than 3/2 power of displacement. The theory is extended to a large range of forces in consideration of the increase in the number of contacts per sphere in the loading process, and theoretical results are compared with experimental results.

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This study investigates the free vibration mode for Ni-base single crystal and directionally solidified (DS) superalloy cantilever plates using three-dimensional finite element analyses. The elastic anisotropy had significant effect on the eigenfrequency and eigenmode of plates. The rotation of the crystal axis around the [001] axis had a smaller effect at low frequencies but had a significant effect at high frequencies. The deviation of the crystal axis in the plate had a significant effect on the eigenfrequency at low frequencies as well as high frequencies. The bulk elastic modulus of DS plates derived by means of the Reuss average was effective to estimate the eigenfrequencies of DS plates. Eigenfrequencies of DS plates could also be predicted by averaging the eigenfrequencies of single crystals which comprise DS plates.

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It is important to establish a bond casting technology which incorporates two different functional materials. Double-layered cylinder liners consisting of an inner layer (wear-resistant, flake-graphite cast iron) and an outer layer (high-strength, cast steel) were cast by the centrifugal casting method. The suitability of these double-layered cylinder liners was confirmed to be able to put the practical manufacture for large-bore diesel engines.

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Nanometer-scale microstructural change that occurs during thermal aging of the ferritic phase of duplex stainless steel was analyzed with a pulsed-laser-atom probe. In addition, changes in electrochemical behavior and the magnetic hysteresis loop were examined and an attempt was made to correlate them to the microstructural change. In this study Fe-19% Cr-10% Ni-2% Mo cast duplexstainless steel was aged at 475°C for 443h. Important conclusions are as follows. (1) Aging promotes the phase separation of the steel into a Cr-rich region (α') and a Fe-rich region, which form a possible 3D modulated structure with a wavelength on the 10 nm order. (2) The electrochemical reactivation peak in the aged steel may result from the Fe-rich region with Cr concentration below 14 at%. (3) The nanometer-scale microstructural change causes hardening and increases hysteresis loss.

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Specimens of tetragonal zirconia containing 3 mol % Y₂O₃ (Y-TZP) were ground with a diamond wheel of grain number 200/230. The residual stress and the monoclinic content were measured by the X-ray diffraction method. The bending stress was applied in the directions parallel and perpendicular to the grinding direction of the specimen. The residual stress on the ground surface was compressive, and the compression zone extended to about 30 μm in depth. The monoclinic content on the ground surface was raised to 7 to 8 percent. The bending strength increased in both directions because of the residual compressive stress near the surface introduced by grinding. For ground specimens, defects at the nucleation site of bending fracture were pores or coarse grains, but not grinding defects. Since the lower content of Y₂O₃ near the nucleation site raised the toughness of the material, the fracture toughness for fracture from small defects was larger than that of the single edge precracked specimen. The increase in the Weibull modulus due to grinding was discussed on the basis of fracture mechanics.

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Strength analyses were performed for bellows reinforced by rings subjected to internal pressure or axially compressive movement, using a finite element computer program. In the present analyses, the contact between the bellows and the reinforcing rings was taken into account, together with the geometrical and material nonlinearities. The results of the reinforced bellows were compared with those of the bellows without reinforcing rings to clarify the effects of reinforcing rings. It was found from the analyses that the reinforced bellows show extremely high loading capacity for internal pressure, compared with the bellows without reinforcing rings. However, it should be noted that the reinforcing rings have adverse effects on the behavior of bellows when the reinforced bellows is subjected to axially compressive movement exceeding the critical value, at which the bellows is fully in contact with the reinforcing rings except at the crown.

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An analysis method for evaluating the sensitivity of bucking load in geometrically nonlinear finite element methods is developed. By pursuing the pseudo-critical point in the perturbed system on the surface of the hypercylinder where the original critical point exists, the sensitivity of buckling load is estimated. Compared with other methods, the present method can cope with both snap-through and bifurcation problems without an eigenvalue analysis. In addition, the load sensitivity at arbitrary points on the equilibrium path can be calculated under the total-displacement constraint condition. Two examples of sensitivity buckling analysis of shell structures are demonstrated to examine the validity of this method, and satisfactory results are obtained.

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An evaluation of thermal shock resistances for structural ceramics was conducted by employing various types of Vickers-indented specimens with different Biot moduli. Then, examination of the correlations between thermal shock resistances obtained by the author's method and usual thermal shock resistances, such as thermal shock fracture resistance and thermal shock damage resistance, was conducted. As a result, the correspondence between the minimum thermal shock condition required for the onset of propagation of generated microcracks and the thermal shock fracture resistance was recognized by conducting repeated thermal shock tests using thicker SiC specimens which have larger Biot moduli. The amount of crack growth per thermal shock cycle implies the same meanings as thermal shock damage resistance for various structural ceramics.

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The basic objective of this study is to establish the material design concepts for the coexistence of good mechanical properties with super heat-resistance in the systems of ceramic/metal and ceramic/ceramic FGMs. Flexural and fracture toughness tests were conducted on gas-pressure combustion sintered Cr₃C₂ ceramic and its composites with Ni and TiC (Cr₃C₂/Ni, Cr₃C₂/TiC) in a vacuum environment up to 1200°C using a newly developed materials testing system. Fracture characteristics were investigated on the basis of fracture mechanics and fractography. The toughness of Cr₃C₂ can be improved by the addition of metallic particles. It is found that the principal mechanism of toughness improvements in these composites (ductile-phase reinforced ceramic matrix composites) is attributed to crack tip blunting by a ductile metallic phase.

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A fretting fatigue test machine for ceramic materials was designed and fabricated to investigate the fretting fatigue properties of ceramic materials. Fretting occurred at the contact surface between the rectangular specimen which was maintained under static fatigue conditions and the cylindrical contact piece. The major factors which affect the fretting fatigue prorerties such as relative slip amplitude and contact load can be controlled and their values can be measured in the test machine. Preliminary experiments were carried out using HIP sintered silicon nitride. Fretting reduced static fatigue strength of silicon nitride. Fretting damage was observed on the contact surface under small relative slip amplitude which never produced fretting damage in the case of metallic materials. Since fretting cracks are initiated at a very early stage of fatigue life, crack propagation life is domenant in fretting fatigue life.

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In the previous report, it was found that high-cycle fatigue strengths were accurately estimated by a multivariate analysis on basic material factors such as chemical composition and heat treatment temperature, under limited conditions which were classified by the materials used, the heat treatment conditions and/or a fatigue fracture mode. The prediction procedure using a material strength database system (DIMS) was newly developed. In this report, the same procedure using DIMS is applied for the prediction of low-cycle fatigue properties such as cyclic stress-strain curves and low-cycle fatigue lives and is examined for several published data sets. It was found that the prediction procedure developed in the previous report is also quite suitable for the prediction of low-cycle fatigue properties.

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Microscopic stress analysis of composite materials is important for evaluating the strength of structures made of composite materials. However there are many cases in which it is impossible to calculate stresses of heterogeneous composite materials by means of the finite element method because of the material's complex geometry. Therefore, heterogeneous composite materials are treated as homogeneous materials. A homogenization method has been proposed to evaluate accurately the microscopic stresses of heterogeneous composite materials. We develop a homogenization analysis system based on a general-purpose finite element method code. To discuss the efficiency and the accuracy of this system, numerical experiments are conducted. This paper presents a basic study to investigate microscopic stresses of soft composite materials.

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In this paper we investigate a method to measure plastic strain of metals with no contact using the laser speckle method. This method is based on observation of the change in laser speckle pattern depending on surface profile change occurring due to plastic deformation. The analysis of the laser speckle pattern is performed using an image-processing system. The relationships between speckle pattern and surface roughness or frequency characteristics of the surface profile were investigated in this study. Surface roughness and surface profile were observed for steel specimens polished with emery papers or plastically deformed. The surface profile diagram was analyzed by means of the Fast Fourier Transform with a computer and the distribution of frequency was obtained. The results show that distribution of light intensity of the speckle is related to frequency distribution of the surface profile, but the distribution of the laser speckle is not always related to surface roughness. It was also clarified that the laser speckle pattern is closely related to the magnitude of plastic strain.

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The thicknesses of bone and bone marrow in a pig femur covered with flesh by inserting a hip prosthesis stem are investigated nondestructively by means of an ultrasonic pulse echo method. An ultrasonic wave is emitted toward the hip prosthesis stem via a normal probe attached to the flesh, and the distances from the normal probe to the boundary surfaces of bone and hip prosthesis stem are measured by observing the time intervals between each echo. Subsequently the actual thicknesses of flesh, bone and bone marrow are measured using vernier calipers. The results of the ultrasonic wave and vernier calipers measurements are graphically presented and compared. It is clarified that the ultrasonic method is useful for practical applications on the proposed problem.

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