In order to study the influence of the grain size and PSZ reinforcement on fatigue strength characteristics of alumina, cyclic fatigue tests were carried out on sintered alumina (Al₂O₃) with a surface crack. The crack was introduced by Vicker's indentation method under two load levels, 98N and 294 N. Fatigue strength tests were conducted at a constant stress ratio R(=0. 1) and constant frequency f(=50 Hz). It is shown that there is large influence of grain size on fatigue strength characteristics and the larger-grained alumina has a longer fatigue life. It is also found that PSZ reinforcement is effective in enhancing the fatigue strength of alumina.

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A specimen gripping device was newly developed for accurate evaluation of the axial cyclic fatigue strength of ceramics at elevated temperatures. The push-pull fatigue tests were successfully performed for the sintered silicon nitride ceramics in the temperature range from room temperature to 1200°C, using the closed-loop-type electrohydraulic test system equipped with this device. The cyclic fatigue strength decreased at 1000°C, compared with that at room temperature. Meanwhile, this showed a tendency to increase as test temperature rises from 1000°C to 1200°C through 1100°C in the long life range. As a result, the slope of a S-N curve decreased with increase in test temperature. The cyclic fatigue test increasing stress amplitude stepwise under stress ratio R=-1.0 at 1100°C and 1200°C, in which the stress level in the first step was below fatigue limit, raised fatigue strength far over the static tensile strength. Almost the same result was obtained from the fatigue test increasing mean stress at the fixed stress amplitude at 1200°C.

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Fast fracture tests at room temperature and static fatigue tests at 1000°C on silicon nitride were carried out, and the relationship between the fracture condition and the defect which leads to specimen failure was investigated using a scanning electron microscope. Furthermore, the crack propagation parameters, A and n at 1000°C, were determined from the fast fracture strength distribution at room terperature and the fatigue life distribution at 1000°C using the specimens having microcracks introduced using a #200 diamond wheel. These parameters were used to discuss the correlation between the fast fracture strength at room temperature and the static fatigue life at 1000°C. The conclusions obtained are summarized as follows : The static fatigue life distribution at 1000°C obtained from the experiment does not coincide with the distribution predicted from the fast fracture strength distribution of the annealed specimens at room temperature. Moreover, the kind of defect which leads to specimen failure and the site of fracture origin change with the change of fracture conditions.

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The initiation and propagation behavior of short fatigue cracks emanating from a sharp notch in an aluminum alloy (2024-T6) reinforced with 20 volume percent of SiC particles was investigated. The development of crack closure with crack propagation was measured through the compliance method. The propagation rate, dc/dN, of short cracks was higher than that predicted using the dc/dV-ΔK relation for long cracks. For the case of a low stress amplitude, the propagation of short cracks decelerated and finally stopped. The relationship between dc/dN and the effective stress intensity range, ΔK_eff, for short cracks at notches was identical to that obtained for long cracks. The relationship between dc/dN and ΔK_eff/E(E=Young's modulus) was nearly identical for short and long cracks in reinforced and unreinforced alloys. The roughness of the fatigue fracture surface was determined using a computer image processing method. The roughness of the fracture surface of composites was larger than that of unreinforced aluminum alloy.

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In order to study the influence of cyclic load on the crack propagation behavior of sintered alumina, static and cyclic fatigue crack growth tests were carried out over a wide range of fatigue crack growth rates. In the case of cyclic load, crack growth tests were conducted at a constant stress ratio R(=0. 1) and at three levels of frequencies f : 1 Hz, 10 Hz and 50 Hz. Further tests were carried out at a constant f(=10 Hz) and at three levels of R : 0. 1, 0. 5 and 0. 8. The crack growth rate da/dN as independent of frequency. In cases of R : 0. 1 and 0. 5, the crack growth rate in cyclic fatigue was higher than that in static fatigue. In the case of R=0. 8, the crack growth rate in cyclic fatigue was almost identical to that in static fatigue. The effective stress intensity factor range ΔK_eff is also a useful parameter to evaluate the cyclic fatigue crack growth characteristics.

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A study on the initiation of quasi-cleavage (QC) crack in the early stage of delayed fracture process has been made by means of a fractographic approach in cathodically charged, quenched and tempered SNCM439 steel. QC crack is the origin of delayed fracture, and the mechanistic condition of delayed fracture is characterized by two parameters : QC crack length and the nominal applied stress. SEM fractographic examination revealed that QC fracture which is characteristic of the early stage of delayed fracture initiates around nonmetallic inclusions and grows mainly in the rolling direction only under the hydrogen charging condition without stress and that the nominal applied stress causes the QC crack to grow in the plane of principal stress.

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The interaction between a crack and a grain boundary is studied by the singular integral equation method. The dislocation wall model is used for representation of a low-angle grain boundary and the crack is assumed to be described by the continuous distribution of infinitesimal dislocations. The problem is first reduced to a system of singular integral equations with standard Cauchy kernels, which is solved by using the Gauss-Chebyshev integration formula, and then the stress intensity factors at the crack tip are calculated numerically. The influence of the distance and angle between the crack and dislocation wall, length of dislocation wall and the dislocation spacing of the wall on the stress intensity factors is examined. Finally, the correspondence to single dislocation-crack interaction obtained using the Rice-Thomson model is discussed.

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Fracture of an inhomogeneous material is characterized by fractal parameters. Acoustic emissions(AE) during the fracture of the material are characterized by the fractal dimension b which is the slope of the log-log frequency-energy distribution. Microcracks in the material are also characterized by the fractal dimension D_L which is the slope of log-log frequency and length distribution. To examine the relationship between the b-value and microscopic fracture behavior, a fracture simulation of inhomogeneous materials is developed using an elastic network model. This model is composed of brittle stick elements, and the inhomogeneity is provided by the distribution of the strength of these stick elements on the basis of Weibull distribution. The numerical calculations were performed for various strength distributions. First, to verify the simulation, the results of the calculations were compared with experimental results of rock from the viewpoint of the AE behavior. The comparison shows that the calculations using the elastic network model can simulate the microscopic fracture in inhomogeneous materials. Then, the simulation results indicate that the change in b-values for AE corresponds to the change in D_L-value for microcracks during the fracture.

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For evaluating the mode I crack-tip stress intensity factor, K_Itip, of cracks with fiber bridging in fiber-reinforced plastics, a method based on measurements of crack opening profiles is proposed. The values of K_Itip and the bridging stress intensity factor, K_{I bridge}, can be separately determined with good accuracy by the boundary element calculation based on measured crack opening profiles. This method was applied to the growth of interlaminar cracks in unidirectional carbon/epoxy laminates, Toray T800H/# 3631, under mode I monotonic loading. The measured value of the crack opening displacement of interlaminar cracks with fiber bridging was smaller than that without fiber bridging. The critical value of the applied stress intensity factor, K_{I ap, c,} increased with crack extension, while the critical value of K_{I tip} obtained from the proposed method took a constant value, K_{I tip, c}, during crack growth. Therefore, K_{I tip} is the true crack-driving force and the true resistance of crack growth is given by a material constant, K_{I tip, c} for the laminates with fiber bridging.

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The purpose of the present study is to investigate the effect of specimen thickness on the fracture toughness of PMMA under impact loading. A dynamic finite-element method and a strain gage method are applied to measure the dynamic fracture toughness. Further, problems on determining the dynamic fracture toughness by the present technique are investigated. Consequently, the following conclusions were drawn : (1) The dynamic fracture toughness of PMMA becomes larger as the specimen thickness decreases from 15 mm to 5 mm. (2) The fracture toughness of PMMA increases rapidly as the loading rate increases in the range between 1. 3×10⁴ (MPa√m/s) and 6. 7×10⁴(MPa√m/s). (3) The measurement of the dynamic fracture toughness by the present method is limited to the higher range of loading rate.

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A piece of piezoelectric ceramics attached to an aluminum alloy plate was subjected to voltage, and surface displacements of the opposite side were detected by a capacitive displacement sensor. The source waveforms were calculated by a deconvolution integral using Green's function. It was demonstrated that the shape of source waveforms due to the step function of voltage is a triangle, and the rise time of the waveform depends only on the resonance frequency in the thickness direction of ceramics. A wide range of the frequency spectrum of the source waveform was obtained. It was also found that source waveforms due to one period of the sine function of voltage contain three peak values. The shape of waveforms was varied by frequency and phase of applied voltage. Consequently, the artificial AE source using piezoelectric ceramics will be useful for source waveform analysis. Also, it is convenient to prepare learning waveforms for the waveform analysis using a neural network.

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The characteristics of a simulated AE source using piezoelectric ceramics were discussed. A small piezoelectric ceramic plate located near the crack tip of a chevron-notched PMMA specimen was subjected to a step voltage for generating simulated AE waves. AE waveforms due to piezoelectric ceramics were monitored with a 6-channel measurement system. A tensile test of the specimen was also conducted to investigate the correspondence with actual AE caused by crack extension. The radiation pattern of the simulated wave suggested the occurrence of mode I deformation at the simulated source. According to the moment tensor analysis, the direction of force was considered to be approximately normal to the crack surface. It is found that although there are a few types of deformation during crack extension, the simulated AE source using piezoelectric ceramics has the same main component as one of those in the fracture. The simulated AE source using piezoelectric ceramics is equivalent to the dipole source of mode I deformation.

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This paper is concerned with a biaxial eccentric bending compression experiment for the case of equal eccentric at the upper and lower ends of carbon square pipes in the short column range, supported with spherical seats. An emperical formula for calculating the eccentric bending compressive buckling stress σ_cre of the carbon steel square pipes is presented as follows ; σ_cre/σ<cr>=1/(1+α₀), where σ_cr=axial compressive buckling stress, and α₀=factor of eccentricity and mean distance between the wall of the steel square pipes. The measurement reveals that the results calculated by this equation are in good agreement with those obtained experimentally for the short column.

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Various structural ceramics have been developed as heat-resistant materials. However, in some applications it is anticipated that they will be exposed to very-high-temperature environments of the order of thousands of degrees. Moreover, those ceramics are subjected to thermal loadings which change rapidly with time. Therefore, it is very important to investigate their thermal shock characteristics. In this report, the distributions of temperatures and thermal stresses of cylindrical-shaped Al₂O₃ ceramics under irradiation by laser beams are analyzed using the finite-element method. Critical fracture curves are obtained from the relationships between spot diameters of laser beams and maximum values of thermal stresses for various power densities of laser beams. The irradiation experiments lead to these critical fracture curves, and both theoretical and experimental curves are in good agreement.

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Development of anisotropy during cold rolling of an aluminium sheet is investigated experimentally and theoretically with respect to flow stress and γ-value in tensile tests. The crystallographic textures are detected by X-ray diffraction, from which the crystal orientations are determined and then incorporated into the finite-element polycrystal model. The numerical simulations of plastic anisotropy show good agreement with the experiments.

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A rigid-plastic finite element method which takes account of the effect of elastic deformation is proposed. In the present formulation, the nodal forces for elements undergoing rigid-plastic deformation are equilibrated with those undergoing elastic or elastic-plastic deformation at the end of each deformation step. The nodal forces for the elastically or the elastic-plastically deforming elements are derived by considering the rotational effect of the elements during deformation. Plane-strain bending of a plate using a round punch is simulated by the present method under a mixed condition of rigid-plastically and elastically deforming elements in the plate. The elastically deforming element is converted to rigid-plastic one after satisfying the yield criterion, although all the elements are set to be elastically deforming at the beginning of the bending. Deformation behavior in the early stages of bending is successfully calculated. The calculated springback angles are in reasonable agreement with the experimental ones for aluminum plates, because the stress distribution in the elastic region which does not attain plastic deformation around the edge of the plate is taken into consideration.

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In this paper, the systematic analysis of the strength and deformation and the reinforcing effect of rings as a whole is discussed, utilizing the method introduced by this author. Consequently, it is found that the influence of the distance between rings is remarkable. When the distance is consider-ably large, the behavoir of the stress and deformation becomes very complicated near the rings, large axial bending stress occurs at the ring portion, and the reinforcing effect of rings is localized. On the other hand, when the distance is very small, the magnitude of the stress and deformation of the shell at any portion between rings becomes almost equal, and the reinforcing effect of rings extends in the entire region of the shell. This finding indicates that the investigation for the local bending is not sensible, and the probability of constructing an optimum structure in the case of using a short ring pitch exists. Therefore, the latter subject will be discussed in a forthcoming paper.

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A computer program was developed for evaluation of the Haasen-Sumino dislocation kinetics model in which the creep strain rate is related to the dislocation density. This model extended to the multiaxial stress state was incorporated into a finite element elastic creep analysis program for axisymmetric bodies. The time variations of dislocation density and stress were obtained by use of this program for a silicon bulk single crystal with about 6 inches in diameter. It was found from the present analysis that the dislocation density increases very rapidly from the initial state to the steady state.

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The stresses of band adhesive butt joints, in which the interfaces were partially bonded, were analyzed using a two-dimensional theory of elasticity, in order to establish the fracture criteria when the joints of dissimilar adherends were subjected to cleavage loads. In the analysis, the dissimilar adherends and the adhesive were replaced with finite strips when the interfaces were bonded by an adhesive at two regions. In the numerical calculations, the effects of the ratios of Young's modulus among adherends and an adhesive, and the thickness of the adhesive, the bonding area and the position on the stress distributions at the interfaces were demonstrated. As a result, it was seen that band adhesive joints were available when the bonding area and positions were determined taking into account external loads distributions. For verification, experiments were performed on the strains of adherends and the joint strength. The analytical results were consistent with the experimental ones.

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This study deals with the thermal stress and strain distributions in an adhesive butt joint which is composed of two hollow shafts. The butt joints are joined by an epoxide-type adhesive and kept at a constant temperature. In the analysis, when the shafts and an adhesive are replaced with finite hollow cylinders respectively, the temperature distribution in a joint is calculated based on the thermal conditions of the joint. Then, thermal stresses are analyzed as a three-body contact problem by the axisymmetric theory of elasticity. The effects of the ratios of Young's modulus, the coefficient of thermal expansion and the thickness of the adhesive on the thermal stress distribution at the interface between the adherend and adhesive are studied as general cases. Moreover, thermal stress in the joints of hollow and solid shafts under uniform temperature change is examined by numerical calculations as special cases of the joints. In the experiments, an adhesive is modeled by an epoxide disc-shape plate and the thermal strains are measured by strain gages which are mounted on the outer surface of the shaft close to the interface between the shaft and the epoxide plate. The analytical results of the thermal strain distribution are compared with the experimental ones measured by the strain gages and it is shown that they are in fairly good agreement.

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Transient heat conduction analysis of hybrid laminated composite materials is very important because they are heated during the manufacturing process. Anisotropy of thermal conductivity must be considered for heat conduction analysis of such composite materials as FRP. Assuming that heat conducts uniformly in a normal direction in thin shells, shell structures can be modeled with membrane elements. This paper presents an FEM transient heat conduction analysis system for hybrid laminated shell structures. This program can treat the orthotropic materials whose principal direction is inclined to the coordinate axes of elements. The temperature distribution of cross section of an Aluminum-CFRP hybrid laminated plate is investigated. And the effect of fiber orientations for the heat conduction of CFRP cross-ply plates is discussed. Furthermore, the heat conduction of CFRP cylinders considering the heat transfer condition is analyzed.

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A thermal stress problem of a coated half-space due to a point heat source is solved exactly. The solutions of the Fourier integral form are obtained, and it is shown that they can be transformed into a series of known functions from which the thermal stress singularities can be obtained in the closed form. When the point heat source located at the interface between a layer and a substrate, the normal stresses have singularities of logarithmic type and the shear stress shows a jump at the point of the heat source. The intensities of the singularities are expressed in the form of products of three factors which depend only on thermal conductivities, mechanical properties and interaction of the thermal expansion coefficient and mechanical properties. The results show that there exist pairs of materials for which the singularities disappear or the normal stresses become compression.

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Because of necessity for the wide engineering applications of triaxial woven-fabric-reinforced plastic (T. W. F. R. P. ), We have carried our stress analysis on the model of T. W. F. R. P. under tensile-constant deformation using a 3-D FEM. Principal stress and strain distribution, the largest values in the maximum principal stress and their location, the surface depression in the model, and Young's modulus of the model were obtained. The results were discussed for varying parameters of the fiber strand.

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Recently, laminated composite plates have been applied to many aircraft structures because their mechanical properties are superior to the conventional materials. Since the laminates have anisotropic elastic properties, the optimum design is reqired to make the best use of the composite laminates. The authors have proposed a successful object-oriented expert system to design the laminated composites with actual constraints. A solution to optimize the fiber orientation of stiffeners around the open hole, however, has not been developed because it is very difficult and reqires stress redistribution analysis. In this study, therefore, the genetic algorithms were applied to solve the optimization problem with the object-oriented finite-element stress analysis method. Results obtained were as follows. (1) The GA method is applicable to an open hole model. (2) The random search method is applicable to any model.

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CF/PEEK composite plates have high delamination resistance because of the high fracture toughness of PEEK. Several studies have been conducted to obtain the delamination resistance. Few delamination micromechanisms, however, have been studied. In particular, the micromchanism compared with that of CF/Epoxy composites is important for the material designing but there are few studies about it. Thus the objective of this study is to measure the delamination resistance of that of mode I and II, considering the micromechanism in comparison with that of CF/Epoxy composites. Results of mode I and II delamination tests indicate that the fiber-resin interface debonding has an important effect on the delamination resistance of CF/PEEK. Additionally, the stick-slip phenomenon model was considered, comparing with that of the CF/Epoxy composites.

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Frequency dependence of magnetically induced amplitude change (MIAC) of longitudinal wave is experimentally investigated for JIS-SS41 low-carbon steel. The amplitude of an elastic wave that propagates in a ferromagnetic material is smaller in the demagnetized state than that in the magnetically saturated state, which is the pure elastic state. This occurs because of the existence of magnetoelastic interaction and microscopic eddy current. When an external magnetic field is applied, the amplitude increases accordingly. Since stress causes reorientation of magnetic domains, the MIAC depends on the stress. In this study, effects of stress and frequency on the MIAC are investigated. It is found that the MIAC depends on the stress and that the frequency dependence of the MIAC is affected by the sign of the stress. The results are applied to nondestructive evaluation of the residual stress in a butt-welded specimen.

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Pulsating compression tests are performed in order to investigate the possibility of applying the copper electroplating method of stress analysis to measure the contact pressure between two bodies. Namely, the relation among density change of grown grains in copper foil inserted between contact surfaces, the magnitude of cyclic pressure σ_p and the number of cycles are examined by computer image processing, and can be expressed by a rate process equation. On the basis of this equation or the relation between σ_p and grown grain density at the given number of cycles, contact pressure and its distribution can be evaluated by observing the density or density change of grown grain.

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Two-dimensional Fourier transform analysis is presented as an advanced method for numerically processing the Young's fringes diffraction pattern from a double-exposure speckle photograph. The fringe spacing and orientation are determined using only one Young's fringes pattern without any other diffraction halo patterns. This algorithm is based on the 2-D FFT of the fringe pattern with 256×256 pixels. Therefore, it has enabled automatic analysis to be performed with noisy and poor fringe patterns. The measurement of deformation field by the laser speckle method can be carried out with higher accuracy, reliability and speed.

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Patellar dislocation is one of disorders that occur in the patello-femoral joint. In this study, the mechanism of patellar dislocation is analyzed using a mathematical model. First, the force exerted on the patella with contraction of the quadriceps in full extension was formulated. To utilize this formula, the following values were obtained from plain radiographs and CT images of the knee joint of healthy subjects : direction of the patellar tendon with and without contraction of the quadriceps and inclination of the femoral trochlea. Then the direction of the force in the patellar tendon, quadriceps and patello-femoral articular surface was determined. The three-dimensional shape of the patello-femoral joint was replicated using the CT images of a representative healthy subject. Finally, the movement of the patella is analyzed from the resting position to the quadriceps-contracted position using a computer-assisted mathematical model. The following parameters were assessed as possible factors which cause in the mechanism of patellar dislocation : (1)the direction of the resultant force of quadriceps in the A-P view, (2)the direction of the patellar tendon in the A-P view, (3)the inclination of the femoral trochlea. Among these parameters, the resultant force of quadriceps and the patellar tendon seemed to exert similar influences on the occurrence of patellar dislocation. On the other hand, the inclination of the femoral trochlea had less of an effect on patellar dislocation. Additionally, the motion of the patellar from the resting position to the quadriceps-contracted position is visualized with the three-dimensional computer model.

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Optimum design analysis in engineering is generally formulated as a problem of nonlinear programming or nonlinear mixed integer programming including selection among alternatives. However, all working methods presently available for linear mixed integer programming are confined essentially to linear problems and are short of versatility. To overcome this situation, a new procedure for nonlinear mixed integer programming with constraint functions was developed for solving general optimum design problems. In this paper, an application study on well design is presented as an example to verify the usefulness of the developed optimization procedure.

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