Fatigue characteristics. of ADI were elucidated by a rotating bending fatigue test. Two types of specimens, heavily (H_v≥400) and lightly (H_v≃320) polished on the surface, were used for the test. The S-N curves of both types of specimens show the double stage of fatigue limit. A fish-eye pattern was observed on the fracture surface of heavily polished specimens in the period of 10⁶ to 10⁷ cycles. It was presumed that the microporosity under the surface combined with work hardening on the surface, caused the double stage of fatigue behavior and the fish-eye patterns.

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The influence of carbon content on fatigue crack initiation behavior has been investigated on three kinds of carbon steels with the same size of ferritic grains by the plastic replica method. The fatigue tests have been mainly performed under the stress level larger than the fatigue limit of each material by the same magnitude, using the rotating bending fatigue testing machine. From the experimental results, the carbon content of each material affects the crack initiation behavior under the same stress amplitude for the three kinds of carbon steels, comparing with that under the stress level larger than the fatigue limit of each material by the same magnitude. In addition, the carbon content of material hardly affects the crack propagation behavior. It is considered that the above result is due to the restriction of plastic flow by pearlitic grains.

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Fatigue properties of polycrystalline copper films subjected to pulsating stresses are investigated on the basis of observations of surface topography, fracture surface and dislocation structure. Fatigue limit corresponding to 10⁷ cycles of a rolled copper film is 2. 3 times higher than that of an annealed one, but the fatigue limit ratio of the rolled specimen is lower than that of annealed one. From the observations of the surface crack and fracture surface, it is found that fatigue crack initiation and early-stage crack growth mechanisms of annealed bulk copper are not necessarily applicable to those of film. No striations are formed in both films. In annealed films, cell structures are formed under high-cycle fatigue whereas no band/ladder structures are formed. Dislocation structures near the fatigue crack in annealed films are similar to those of bulk specimens except for the absence of intensely elongated cells observed in the shear flow regions in the bulk specimen. No appreciable change during fatigue was found in the dislocation structures of rolled films.

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The factors relevant to the fatigue strength of cold-drawn eutectoid steel wires were examined. Results were summarized as follows : The fatigue limit of eutectoid steel wires increased with drawing strain (ε=2lnd₀/d), where do and d are diameters before and after drawing) until about 2. 5, and then decreased. In the case of ferritic steel wires, however, the fatigue limit was almost constant, while the fatigue life increased with drawing strain. The fatigue limit increased with decrease of specimen diameter. The interlamellar spacing did not influence the fatigue limit. With an increase of drawing strain, the ratio of the period of crack initiation and initial propagation to the fatigue life increased. This ratio in eutectoid steel with larger drawing strain was high as compared with that in farritic steel.

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Rotating bending fatigue tests were carried out in order to clarify the correlation between fatigue strengths of pit-type notched and circumferentially notched specimens of 0. 16% carbon steel. The obtained results show that the notch radir of the branch point ρ₀ are almost the same and about 0.6mm in the two types of notched specimen. It is found that the fatigue strengths of the two types of specimen can be estimated on the basis of linear notch mechanics. Moreover, the master curves of K_tσ_w1 and K_tσ_w2 vs 1/ρ for the two types of specimen are equal. This implies that the fatigue strength of the specimen with a defect may be estimated from the fatigue strength of a circumferentially notched specimen.

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It is important to estimate the effect of small surface defects on the fatigue strength. Therefore, many studies concerning the surface defects have been performed especially in air. For the corrosive environment, however, there have been few studies. In the present study, rotating bending fatigue tests of smooth specimens having different sizes of a small blind hole were carried out in 3% NaCl solution. Successive observations of the surface were made by the plastic replica method to clarify the generation behavior of the corrosion pit and the initiation behavior of a crack. The crack propagation behavior was investigated based on the dl/dN versus l relation. The dl/dN versus l relation indicates that the growth rates of cracks having the same length but different histories are not necessarily equal.

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In order to estimate the crack initiation behavior at the corners of square inclusion and square hole in rubber material by fracture mechanics, a static tension test is carried out. The direction and load for the crack initiation are measured. The finite element analysis of the stress distribution in the vicinity of the corner point is also performed. By the consideration based on the concept of the linear fracture mechanics, it is found that the direction of the crack initiation is estimated by the maximum value of the governing component of a stress σ_θ for the singular stress field near the corner. It is also found that the initiation load is characterized by a stress singularity order and a parameter K^* which govern the stress field near the singular point.

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In this paper, an analytical solution is presented for stress intensity factor of a solid circular cylinder with an edge crack subjected to transient hygrothermal loading on the lateral surface. It is assumed that the coupled diffusion problem of temperature and moisture in the cylinder over a short time can be analyzed by neglecting the hygrothermal disturbance near the crack tip. The associated plane-strain hygrothermal stress problem is solved by the use of Tweed and Rooke's solution for a pure elastic problem in a circular cylinder with the same crack. Numerical calculations are carried out for the stress intensity factor at the crack tip in the circular cylinder made of T300/5208(graphite/epoxy) composite material. The effect of crack length and coupling of temperature and moisture fields on the stress intensity factor are quantitatively estimated under various thermal and hygrometric loading conditions.

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Advanced fiber-reinforced composite materials have been used for structural members because of their high specific strength and stiffness. This paper deals with the problem of dynamic stability of cross-ply laminated cylindrical shells subjected to axial compressive step loading. First, the axially symmetric motion of the shell under the loading is determined. Subsequently, certain perturbations are superimposed on this motion, and their effect on the behavior of the shell is investigated. The symmetric state of motion of the shell is called stable if the perturbations remain bounded. The solutions for the prebuckling motion and the perturbated motion are obtained by the use of Galerkin's method. Stable regions are examined by utilizing a Mathieu equation. The inevitability of dynamically unstable behaviors is proved analytically, and the effects of various factors, such as compressive load ratio, number of layers, static buckling pattern and dynamic unstable mode, are clarified.

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As a fundamental study on the effects of thermal cycles on residual stress of ceramic/metal joints, residual stress in Si₃N₄/Cu/SUS304 joint specimens was measured before and after single thermal cycle by the X-ray diffraction method. X-ray measurement clearly showed the increase in residual stress after the single thermal cycle. After the residual stress measurement, the 4-point bending test was performed. The relationship between the bending strength and the single thermal cycle temperature was examined. The bending strength was found to decrease linearly with the increase of residual stress.

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At present, with the promotion of scaling-up, performance intensification and speeding-up of machines and their structual components, heat intensity problems have become an important issue in engineering. And the study of wear and fractures resulting from heat stress are of great importance in the safety design of such equipment. The stress intensity factor has been used as a measure of the near-stress-field intensity around the crack tip in various fracture problems. It can be determined by using simple equipment and following an easy procedure by the method of caustics, though it can also be obtained experimentally by means of photoelastics. In this study, the relationship between the stress intensity factor and the time or the depth of the crack in the blocks (made of polymeric materials such as epoxy and acrylic resin) with their crack side subjected to heat loading was investigated.

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A study has been conducted on the residual stress distribution in a thick-walled tube for an Al-SiC functionally gradient material manufactured by the centrifugal method. An ingot of Duralcan F 3 D. 20S of Al-20vol%SiC composite was adopted as a master composite. The applicability of a curved beam theory with a consideration of a gradation of elastic properties was first examined by a ring compression test. The circumferential strains generated by the residual stress were measured based on a cutting test and were in a range from-750 to 500μ strain. The distribution of the residual stress was analyzed as an inverse problem and a numerical analysis was also adopted to solve the thermal deformation of an axial symmetry. When the specimens were cooled uniformly, the yileded stress and strain were changed from compression to tension toward the outside of the ring accompanied by a decrease in the coefficient of thermal expansion. It was concluded that the residual stresses were generated by a cooling of 140 K which was from half the melting point to an ambient temperature. The residual stresses were found to increase with the increase of thermal expansion mismatch and radial thickness of the ring.

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The pseudoelastic behavior associated with the martensitic transformation (MT) of TiNi shape memory alloy under different types of strain variations has been investigated experimentally. The nestles are summarized as follows. (1) If strain varies within the MT region, the MT stress and the reverse transformation stress decrease under cyclic deformation. The properties of decrease in both kinds of transformation stress due to cyclic deformation do not depend on the amount of strain and the types of strain variation. (2) If strain varies beyond the completing points of the MT and the reverse transformation, the overshoot of the transformation stress appears at the starting points of the MT and the reverse transformation and the transformation stress decreases. The higher the temperature and the larger the maximum strain, the larger the amount of overshoot and the decrease in the transformation stress.

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Generally inelastic properties of metal materials depend on the deformation rate. However, past studies on viscoplastic constitutive equations do not successfully describe actual flow stress properties and stress relaxation ones as well as temporal hardening in reloading after relaxation. The authors have experimentally and theoretically examined the effect of strain ageing on a resistance in plastic flow using SCM435 steel. In this paper, both increasing strain ageing during stress relaxation in which strain rate decreases gradually, and temporal hardening in reloading are assessed quantitatively. It is shown that the concept of the viscoplastic constitutive model with consideration of strain ageing has a good applicability to inelastic behavior including relaxation property.

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Changes of intensity distributions of the laser speckle pattern reflected from the aluminum surface under plastic deformation were measured using the image processing technique. The cross section of the laser speckle pattern on a same gray level changed to the ellipsoidal shape from the initial circular shape corresponding to the onset of plastic anisotropy of aluminum. Therefore, the cross section of the speckle pattern was approximated by an elliptic function using the least squares method. The results obtained are as follows. (1) Changes of radii a and b and aspect ratio b/a of the elliptic function approximating the cross section of the laser speckle pattern under plastic deformation are related to the onset of plastic anisotropy, the onset of yielding and localized deformation. (2) In the case of the rolled specimen, changes of the aspect ratio can be divided into the three stages : first is the negligible change in the elastic deformation, second is the large change until the onset of localized deformation and third is the small change after that. (3) In the case of the annealed specimen, the changes of radii a and b due to plastic deformation were very large, but the change of the aspect ratio was very small.

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The present paper discusses the accuracy of finite-element solutions for metals possessing dominant plasticity, resulting in an incompressible response in a large deformation field. It is known that poor numerical solutions are obtained in constrained problems due to incompressibility of deformed metals, but can be improved by selecting element shape function and numerical integration technique, as well as applying the mixed method derived from Lagrangian multipilers. Many studies have been made for rigid-plastic finite-element solutions so far, but largely deformed elastoplastic structural analysis is rarely discussed in the literature. In the present study, we discussed the advantages of such techniques in large deformation analysis using Jaumann stress rate and isotropic hardening hypoelasticity model.

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The previously developed adaptive boundary element h-refinement scheme called "sample point error analysis and related refinement by extended error indicator" is applied to linear thermoelastic analysis. The problem is expressed by two types of boundary integral equations : one for temperature and the other for displacement components, which yield two solution inconsistencies for each sample point. Approximate adaptive iteration schemes to overcome the difficulty and to give sufficiently accurate results are presented. Two-dimensional elastic bodies subjected to thermal as well as external loads are analyzed by the proposed methods. The adaptive boundary element analysis can be performed by specifying minimum information required for defining the problem considered ; the scheme is user-friendly.

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To understand the ink transfer mechanism in mimeographing, the theory of poroelasticity is applied to analyze the ink flow through a screen/printing-master layer which is modeled by a fluid-filled poroelastic layer. The analysis shows the following : (1) some ink is sucked back from printing paper while compression by a press roller declines ; (2) the transfered ink mass is its maximum if the duration of compression is nearly equal to the characteristic time of the layer ; (3)the ink flux and transfered mass can be appropriately estimated by using the effective permeability and elastic modulus defined ; and (4) compaction of the poroelastic layer by the press roller squeezes out ink, which plays a predominant role in the ink transfer.

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This study is concerned with elastodynamic inverse analysis in which unknown plural defects should be identified from displacement responses on the boundary of an elastic body. In the previous paper, we proposed an inverse analysis method for identification of unknown parameters using the boundary element analysis for steady-state elastodynamics. In this study, we introduce a new method to determine model parameters for initially assumed unknowns of inverse analysis using a genetic algorithm. We describe in detail how to apply the genetic algorithm to the inverse analysis. Numerical simulation is carried out for some example problems to identify unknown plural defects, whereby the effectiveness of the proposed method is demonstrated.

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The conventional determination of the optimum blank shape and the limiting drawing ratio is presented, with particular reference to the improvement of the blank design of deep drawing of sheet metal for nonaxisymmetric cups by a flat-headed punch, using an inverse finite-element method. The authors' inverse approach has been applied to a cylindrical cup with a square flange, and square cup, and the prediction was made in terms of the relationships between the optimum blank shape and the drawing height and between the optimum blank shape and the drawing force, as well as the limiting drawing ratio of the optimum blank. The forming limit diagrams of those drawing cups were conceived theoretically, taking account of the die radius, blank shape, coefficient of Coulom's friction and the blank holder force. The theoretical predictions were compared with experimental results in the previous paper, for deep-drawing square cups from optimum blank shapes, and the two results agreed reasonably well.

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It is well known that the attenuation of surface acoustic waves is a useful parameter to estimate the grain size, porosity and microstructure which are closely related to electrical and mechanical properties of materials. In the present paper, a novel method for determination of ultrasonic attenuations in the surface layer of materials through an ultrasonic spectroscopic technique is proposed. The method is based on an absolute measurement of the reflection coefficient of the materials and its spectral behavior analysis. The attenuations are determined by detecting the frequency of least reflection and by estimating a locus of zero points of the reflection coefficients in the complex plane. An experiment with annealed carbon steel was demonstrated. The amplitude of the reflection coefficient calculated with the attenuations estimated by the present method indicated the frequency dependence similar to the experimental result. This reveals that the estimated attenuations are reasonable to evaluate the actual acoustic response of materials.

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It is well known that sunlight induces the ultraviolet (UV) degradation of polymers. This paper describes the effects of UV irradiation on the change of mechanical properties of polypropylene (PP)and polycarbonate (PC) films. After the specimens were exposed to UV light from the fluorescent UV apparatus, some specimens were subjected to a dead load afterwards the exposures. Tensile tests and dynamic viscoelastic mechanical tests were conducted. In addition, infrared spectrum and molecular weight were measured in order to investigate changes in chemical properties. (1) The degradation of mechanical properties due to UV irradiation is divided into two periods, i. e., the degradation-incubation period and degradation-development period. The failure strain does not change in the first period, and gradually decreases with increase of the integrated UV irradiation energy. The applied stress during irradiation has a tendency to accelerate degradation. (2) The temperature during exposure influences degradation considerably when it is greater than the glass transition temperature. (3) The reason for the existence of the incubation period is different for two materials. PP has no active bases originally for light-induced chemical reaction, and thus a certain period is necessary to initiate scission of main chains. On the other hand, PC has active bases but the second conjugation is strong. Therefore a certain number of main chain scissions are required to decrease the failure strain.

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CF/Epoxy composites have been applied to many aircraft structures. The composite plate compression properties, however, are easily decreased by delaminations. Thus an approach for detecting the delaminations, therefore, is widely desired now. In this study, therefore, an electric potential method was discussed for a real time non-destructive evaluation method of delaminations because this method has several advantages comparing with the embedded optical fiber. To obtain the basic properties of the CF/Epoxy composites, mode I and II delamination tests were conducted and the relations between the electric resistance change and the delamination crack length were measured. As a result, the electric resistance bridge circuit approach was proved to be excellent for detecting the delaminations from inside the aircraft structures.

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The distribution of rainflow range is investigated for the Gaussian random process under bimodal PSD. The new method evaluates the distribution of range by taking the sum of two Rayleigh distributions which correspond to two dominant frequencies in bimodal PSD. Representative distribution data have been obtained from rainflow analysis for simulated time histories. The applicability of the proposed method is examined for the range distribution generated by the simulation. It is shown that the method evaluates the distribution of range with high accuracy even for the random wave giving a large irregularity factor in some cases. Since range data for unimodal PSD can be evaluated by Rayleigh approximation, the new method for bimodal PSD greatly extends the region of analytical treatment.

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Tensile tests of a l0vol% boron-aluminum composite were carried out at room temperature, 150°C and 300°C, in order to investigate the validity of the finite-element-method (FEM) simulation proposed in the previous report, which evaluates the tensile strength of fiber-reinforced metals. The average strengths of the simulated result were in good agreement with those of the experimental result, although the range of the variability in strength was somewhat underestimated. The stress distributions on the fibers around a broken fiber were estimated by FEM analysis, by taking into account the matrix constitutive equation at the elevated temperatures. Then, the relation between the stress distributions and the statistical properties of strength obtained in the experiment and simulation were discussed, using the probabilistic model based on the Markov chain. It was pointed out that, consequently, the statistical properties of room temperature are maintained to some degree at elevated temperatures. Additionally, the effect of the thermal stress occurring in the composite on the tensile strength was also investigated.

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For optimization problems of domains in which elliptic boundary value problems are defined a solution is proposed. The treated problems are those to determine the domain that minimizes an objective functional of the state functions under the conditions that the coefficient functions of the partial differential equations and the boundary value functions in the elliptic boundary value problems have smoothness and a one-to-one correspondence with domain variation and that the volumes of the domains are limited. Domain variation is formulated with a speed field. The derivative of the objective functional is obtained as a linear form of a shape gradient function. The solution is formulated by using the gradient method in the functional space of the speed field with the linear form of the shape gradient function. The solution is implemented to analyze the speed field with regard to the deformation field of the linear elastic continuum formed in the objective domain applying the force in proprtion to the shape gradient function.

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