It is clarified that a stress amplitude dependence exists in the relation between the small corrosion fatigue crack growth rate and the stress intensity factor range. This stress amplitude dependence observed in an aluminum alloy shows an opposite tendency to those reported by Gangloff whose experiment was carried out with high strength steel in a simlar environment as the one in this experiment. It is considered that this peculiar phenomenon of small corrosion fatigue crack growth is strongly influenced by the transport process of dissolved oxygen between the bulk solution outside of the crack and the local solution in the neighborhood of the crack tip.

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For strength design of ceramic parts, static bending fatigue tests, namely delayed failure tests, and cyclic bending fatigue tests were carried out at room temperature on smooth specimens, hourglass type specimens and notched specimens of sintered Si₃N₄. (1) Cyclic bending fatigue strength (maximum stress) at stress ratio R=-1 is lower than static bending fatigue strength. It is considered that this is due to the effect of cyclic stress rather than the effect of compressive stress in alternating stress and the difference of effective volume. (2) Both static bending strength and rotating bending fatigue strength of a notched specimen reduced almost at the rate of a stress concentration factor. (3) In case of cyclic fatigue, the mark made by rubbing against each other was observed on the fracture surface of some specimens.

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A scanning laser acoustic microscope, SLAM, is applied to measure velocities of sound and to evaluate elastic constants of ceramics. The method to measure sound velocity is based on spectral interferometry utilizing the interference fringes in a sample and in a reference material. In this study, a suitable sample holder is made to excite the ultrasonic wave to the desired mode, i.e., the longitudinal or the transverse mode, within the sample. Young's modulus, shear modulus and Poisson's ratio of partially stabilized zirconia ceramics are evaluated from the measured velocities of sound. Then, tensile testing is performed on the same sample and the elastic constants are measured. The elastic constants measured by SLAM are in agreement with those obtained by the tensile testing within a deviation of about 10%. The method described here is useful for small ceramic materials.

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Three-dimensional elastic analytical programs were developed using the body force method, where the boundaries of an elastic body were approximated with a set of triangular surfaces, and the densities of the body forces were assumed to be constant in each area. Using this method, the necessary integrals could be obtained analytically and CPU time was shortened. Some typical stress concentration problems were analyzed and the results were sufficiently accurate. As a result, it is found that this simple method is available for general stress concentration problems.

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As another example of heat conduction and plane thermal stress problems in which the solutions are expressed in Mathieu and modified Mathieu functions, analytical solutions in elliptical coordinates are given for both a steady-state temperature field and an associated plane thermal stress problem in an elliptical plate subjected to unaxisymmetric heating on the elliptic boundary with heat transfer on the upper and lower surfaces. When heat loss from the upper and lower surfaces into the surrounding media exists, the temperature function must be expressed in Mathieu and modified Mathieu functions and thermal stresses occur even in a steady-state temperature field. The associated plane thermal stress problem can be formulated in terms of Airy's stress function. Numerical calculations are carried out for the distributions of temperature and circumferential thermal stress in the elliptical plate subjected to unaxisymmetric heating expressed in the form of a fourth-order equation and Heviside step function of the η coordinate on the elliptic boundary.

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The aim of this paper is to analyze the plane-thermoelastic problems in composite hollow cylinders by using the plane-thermal stress theory for nonhomogeneous multiply-connected regions developed by the present authors. This theory was developed by considering the composite bodies consisting of several layers of distinct homogeneous materials as nonhomogeneous bodies. Since this method does not need the consideration of the continuity of temperature, heat flux, stress and displacement at the interfaces, we can analyze the thermal stresses in the composite bodies consisting of three layers of homogeneous materials and layers of nonhomogeneous materials such as functionally gradient material. The thermal stress problems in the composite hollow cylinders consisting of two or three layers of homogeneous metals and ceramics subjected to asymmetric heating on the inner boundary are expressed using the nonhomogeneous thermal stress theory formulated in terms of Airy's stress function and solved numerically using the finite difference method.

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As a basic model of dynamic analyses of the elastic structural elements having some geometrical inhomogeneities, distortion of dispersive waves by a notch on a rod is studied both experimentally and analytically. An aluminium alloy circular rod is notched at its intermediate portion and is subjected to external loads by impinging cylindrical bullets at one end of the rod. Unsteady strain waves are detected by several strain gauges and their waveform analyses are made. Also, the incident, reflected, and transmitted waves and their interferences are simulated using the approximate wave equation that has been already proposed by the present authors.

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Elastic Constants of aluminum solid solution alloys, including noble metals and transition metals, were calculated by means of the pseudopotential method. In these calculations, mean valences and mean atomic volumes for various concentrations of solid solutions were considered and a pseudo-atom alloy model was adopted. Calculated elastic constants qualitatively agreed well with experimental values. These results implied anomalies on elastic constants which were related to screening singularities. Pair potentials were also determined by this pseudopotential in reciprocal space.

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A new method has been developed for the measurement of the flow birefringence of a polymer melt using a modified coaxial-cylinder apparatus. Unlike previous designs, the entrance and the exit of the light beam are formed by two thin cylinders capped with glass plates. This structure prevents the disturbance of the light propagation without causing an appreciable measurement error. Experinental results are given on a sample of high density polyethylene under a steady-state shear flow. The relationship between the stress state and the birefringence is discussed, and the validity of the so-called "stress-optical law" is checked.

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The bonding of ceramics and metals is an effective method for the use of ceramics as structural materials .Generally, there is a serious problem that a significant thermal stress concentration occurs in the ceramics owing to the different thermal properties of both materials. In the previous work, it was found that high axial stress is induced only in the very narrow region near the outer surface of the ceramics. In the present paper, the authors investigate how the thermal stress concentration is influenced by shape of the ceramics of a joint, using the thermoelastic-plastic finite element method. It is found that the stress concentration can be reduced by changing the shape of the ceramics, and that the maximum value of the axial stress as well as the principal stress in the joints with various shapes is estimated by a simplified theoretical analysis.

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Fracture tests of unsaturated polyester resin on large, single-edge notched-bend specimens were conducted under static and dynamic bend tests at room temperature. The velocity of a loading point in the three-point bending was changed from 8.3×10^-6mm/s to 7×10⁵ times its value. The two types of fracture marks of the both-ends-closed mark (like ellipses) and the one-end-opened mark (like parabolas) were observed and they were expressed by the equation of fracture marks. A rocket mark, defined here, was also often observed in the dynamic bending test and was well-approximated by the equation. The experimental number, percentage, relative interference appearing distance and the calculated relative critical distance of the marks changed with the crack propagation distance and the testing speed. The velocity of a primary crack propagation was measured and approximated by a mixed-condition relation proposed by us. This change and the gammer-letter relation between the velocity and a dynamic stress intensity factor K_D (or a dynamic strain energy release rate, S_D) gives the latter (K_D or S_D) as a function of the crack propagation distance. This provides a good theoretical explanation of the above variations of fracture marks.

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Low noise AE waveform analyzing system, especially for ceramics, was established and microcracks nucleated during fracture toughness testing of Al₂O₃ were evaluated using this system. Three dimensional locations of microcracks were carried out using arrival time difference of 6 ch AE waveform signals. In the earlier stage, microcracks were nucleated around the center of notch front, and in the latter stage, their sites were widened through the specimen thickness. Most of these cracks were evaluated as mode I cracks because of the same phase radiation pattern of AE signals detected. Furthermore, the quantitative sizes of there microcracks were estimated as 15-50 μm by AE source characterization. Consequently, after being evaluated these microcracks were classified into two groups based on their sizes, i.e. smaller (15-30 μm) and larger (30-50 μm) cracks. It was concluded that the former were effective microcracks used to enhance the fracture resistance of ceramics, while the latter became the origin for the final unstable fracture.

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An advanced acoustic emission technique was developed to obtain a moment tensor due to microcracking, that allows evaluation of the fracture mode, size and nucleation rate of microcracks. At first, the theory of acoustic emission source characterization was presented by the `eigenstrain method' of micromechanics. This moment tensor can be evaluated by time domain deconvolution of the detected signals, using the transfer function of the measuring system and the dynamic Green's function of the medium. The transfer function of the measuring system can be estimated by means of a simulated signal, while the dynamic Green's function was estimated by computer simulation using the finite difference method. In the case of Si₃N₄ microcracks were located at the front of precrak, and the size estimated was compared with the direct observation in the scanning electron microscope.

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The half-width of diffraction line profile is widely used to evaluate the broadness of a diffraction line. To evaluate the reproducibility in measurements of the half-width B, the standard deviation of half-width, σ_B, arising from counting statistics is derived analytically. It can be calculated from a single measurement. An approximate value of σ_B is given by σ_B=√(2y_m+3y₄))/(√3M) where y₄ is the maximum count, and y_m and M are the X_ray counts and the slope of the side of the diffraction line at half its height, respectively. This equation shows that σ_B depends only on X_ray counts and the slope at half height of the diffraction line, being independent of the half-width. Additionally, σ_B is inversely proportional to the square roots of X_ray counts and preset time.

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It is obvious that not only statistical data, but also human subjective judgments play an important role in determinig the reliability index of a structure. For this reason the author previously proposed a reliability analysis method in which subjective values were treated in the calculation using the concept of a fuzzy set. In this paper, the experimental relation between the subjective evaluation data and objective data is discussed. Carbon fracture test pieces were prepared, whose surface roughness were varied continuously. And their strength were precedently evaluated in liguistic expressions, then 4-point bend tests were conducted. Using the subjective evaluation data, the membership function of the surface roughness was determined, and then the membership function of the strength was presumed by comparing the membership function and the statistical data on the strength. Finally the relationship between two membership functions were argued. This result can be applied to obtain a fuzzy reliability index.

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A simple method for shape optimization of a static elastic body in a sense of uniform strength is newly proposed. The idea from which the method originated came from the growth behavior of living things, such as trees or bones, responding to a stress accompanying a load. On the use of the method, the optimum shape is formed by iterating a usual elastic analysis and incremental growth analysis by using a constitutive equation of growth with the result of the elastic analysis, without a particular technique for mathematical optimization programming or a steep extension of memory for calculation of the sensitivity. The growth law is given as a relation between incremental growth strain and a deviation of objective stress indicating the strength from basic stress. Two examples of a cantilever beam loaded at its tip and a column loaded at its tip under the influence of gravity are analyzed to show the effectiveness of the proposed method.

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For engineering purposes, it often becomes necessary to fit a parabola and a Gaussian function to equally spaced n data points (x_i, y_i) by using the least squares method. Simplified equations for calculating these functions are derived for rapid calculation and to avoid error due to the overflow of figures in the calculation with a computer. The coefficients of the parabola given by y=a(x-x^^-)²+b(x-x^^-)+c are [numerical formula] where, x^^- is the mean and e is a fixed interval of x and [numerical formula] For a Gaussian function given by y=exp[a(x-x^^-)²+b(x-x^^-)+c], the coefficients can be calculated from Eq(1) using c_i, and substituting ln y_i for y_i in Eq(2).

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An estimation method based on the idea of perturbation and inverse solution of the rigid viscoplastic FEM is developed to evaluate the friction at the die-workpiece interface. Numerical simulations of the ring compression test illustrate the ability of the method to determine the varying friction coefficients. Possible estimation deviation in the presence of measurement errors is discussed. The analysis was applied to the measured internal diameter-reduction in height data, and the results revealed some transient features of friction during the process which could hardly have been indicated by the usual calibration curves. This approach was also useful for the problems with the interfaces of different friction conditions.

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A section figure of a fracture surface has been reconstructed from a stereopair of scanning electron micrographs using the personal image processing system. Matching points of the SEM images were detected by three types of the methods : sequential similarity detection algorithm (SSDA), normalized SSDA (NSSDA) and mutual correlation coefficient (MCC). Detecting times for one section (42 matching points) required in SSDA and MCC methods were about 10, 15 and 45 minutes, respectively. Section figures were reconstructed on a fatigue fracture surface of an aluminum alloy and a fracture surface near the stretched zone of a steel. The effect of preprocessing for the SEM image on the detection was studied and suitable techniques for this kind of system were discussed.

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