In order to clarify the effect of grain size on the fatigue limit of pure iron, the effects of prestrain on the relation between the fatigue limit and grain size are investigated through rotating bending tests in the range of 0∼20% prestrain. It is found that the fatigue limit of prestrained as well as annealed material depends on grain size, and the dependence is not affected by the amount of prestrain. Yield stress gradually becomes independent of grain size with an increase in the prestrain. Therefore, it is concluded that the mechanical properties of the material which are influenced by grain size, i. e. yield stress, hardness and so on, are not the major factor in the grain-size dependence of the fatigue limit in both the annealed and prestrained materials. It is also found that the crack initiation stress increases as the prestrain increases, and remains dependent on grain size, while the slip initiation stress is increased little by the prestrain and has a small grain-size dependence.

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A data base of the fatigue crack growth for nuclear component ferritic steels was constructed. Data collected are of the low alloy steels (A533B-1, A508-2, A508-3) and a carbon steel (STS42) tested in air from room temperature up to 371°C. Characterization of the fatigue crack growth data and improvement of the conventional design curve were attempted. A proposed design curve is given as follows ; da/dN = 3.57×l0^-9{(1 + 0.30R)(E₀/E)^0.51ΔK}^3.02 (da/dN : mm/cycle, ΔK : MPa√(m)), where da/dN is the fatigue crack growth rate, R is the stress ratio, E₀ is the Young's modulus at RT, E is the Young's modulus at the temperature concerned and AK is the stress intensity factor range. This equation proved better applicability than the one proposed in ASME.

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The pure creep-fatigue bebavior of 2 1/4 Cr-1Mo steel at 550°C was analyzed by a damage model which was originally developed by the authors for an evaluation of the pure creep-fatigue behavior of 304 Steel at 650°C. The model consists of two damage parameters, that is, the time-independent damage parameter D_I and the time-dependent damage parameter D_D. The applicability of the model to 2 1/4 Cr-1Mo Steel was checked and the model was modified as follows. a) D_I was modified so that it could describe the effect of mean stress. b) D_D was determined as a time integration of the internal stress instead of the overstress It was shown that the above modifications made possible a more reasonable evaluation of the pure creep-fatigue behavior of 2 l/4 Cr-1Mo steel at the temperature.

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The prediction method for analyzing the crack opening area for a pipe is essential for leak-before-break evaluation. Several theoretical approaches are proposed for predicting crack opening areas. One approach is the Tada and Paris formula developed based on linear elastic fracture mechanics. Another approach is the method proposed by German and Kumar who have developed an engineering approach. Round robin analyses for crack opening areas are performed using the above two methods The pipe analyzed is 6-inch diameter Type 304 stainless steel with a circumferential through-wall crack The applied load is a bending moment. The crack opening areas calculated by the Tada's method coincided among the four participants. However, the areas using German's method were quite different It is concluded that the Tada's method is suitable for predicing the crack opening area in the present situation. In addition, material properties used in the calculations of the area are discussed compared with the results of the pipebending experiment.

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Rotary bending fatigue tests were carried out in a sodium chloride aqueous solution by using specimens of 6 and 12 mm diameters in order to investigate the effects of the distributed surface cracks on corrosion fatigue lives or crack growth periods N_p. N_p for specimens of 6 mm diameter decreased with increasing crack density or sum total of crack lengths. On the other hand, N_p for specimens of 12 mm diameter increased with increasing crack density or sum total of crack lengths. These effects of the distributed surface cracks on the crack growth period N_p were explained by taking into account both crack coalescence behaviors and stress relaxation effects at cracked parts.

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In order to investigate the characteristics of surface crack growth behavior, the fatigue test and potential measurement using a simulated surface crack specimen for low-alloy steel (STS-42) were achieved in pure water at a temperature of 50°C and an oxygen content of 2 ppm. The potential observed in the surface crack plane showed that the differences depended on the crack depth. With time, the potential around the. crack surface showed more noble values than at the deepest tip of crack This reason could be explained by the difference in oxygen content along the crack plane due to the effect of water flow and crack shape. The mechanism of the generation of the hydrogen-assisted intergranular fracture mode observed at crack surface was also discussed based on an electrochemical aspect.

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The distribution of residual stress in the vicinity of fatigue crack tips and behind them of S15C, SK-5 were measured by X-ray microbeam equipment. Fatigue cracks were loaded and unloaded and then the behaviors of opening and closing were examined analytically. The results obtained are summarized as follows. (1) A monotonic plastic zone ahead of the crack tip and a cyclic plastic zone was found in the vicinity of crack tip. (2) It was found that the ratios of fatigue crack opening and closing by X-ray measurement were in good agreement with the value by the micro displacement method.

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The objective of the present study is to propose a practical method to evaluate the fracture resistance of a stably growing crack by crack energy density and to verify its applicability. The 1st report proposed the method, and the 2nd to 5th reports showed its applicability to the ductile crack in the thin plate. The present report shows the applicability to a plane-strain fracture in a thick board by inspecting the correspondence of the evaluated fracture resistance to the fracture mode change and to the J-integral. Based on a stable growing crack test with 25% side-groove CT specimens, we get the expected results : (1) The evaluated fracture resistance by the crack energy density becomes constant, corresponding to the stable crack growth with a uniform plane-strain fracture mode observed by SEM (2) The additional rate of the crack energy density agrees with the variable rate of the J-integral to the crack growth.

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A D. C. Electrical potential method has been developed to discriminate between an embedded crack and a surface crack on the back wall and then to evaluate their positions and sizes. The method consists of the following procedures : (1) Calculate two parameters, ΔΦ_max and A, from a measured curve of potential difference distribution, whereΔΦ_max is the maximum potential difference and A is an area characterizing the distribution. (2) Assuming a surface crack, calculate two values of its length fromΔΦ_max and A. (3) If these two values are equal to each other, then the crack is discriminated as a surface crack. ( 4 ) In the case of an embedded crack, calculate the length from A and the depth fromΔΦ_max. It has been found from experiments that the proposed method is useful for discriminating and sizing embedded cracks and surface cracks on back walls.

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Recently, it has come that both reliability and safety are requested to the rotary machines because they are becoming largescaled together with their much higher speed of revolution aiming at better performance. To fulfill these requests, more precise stress distribution in the rotating parts under actual rotating conditions is needed. On the other hand, since the cracks may be initiated at the critical sites of rotating parts and some of them may develop into their final fracture, design concept based on the fracture mechanics should be taken into consideration. This paper deals with photoelastic analysis of the rotating discs having dovetail jointed blades with special attentions of stress distributions along the rotating blade and stress intensity factors K_I and K_II under its rotation of the vacuum condition.

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Pulsed holographic microscopy is applied to kake instantaneous microscopic photographs of the neighborhoods of crack tips propagating through AISI 4340 steel specimens at a speed of about 300m/ s. We use a holographic optical system with a Q-switched ruby laser which records scattered light from crack edges and from specimen surfaces as object light. A method for brteaking the specimens is devised to synchronize the laser oscillation with the generation and propagation of a crack. Two microscopic photographs are obtained. From each photograph, the crack opening displacement (COD) is measured along the crack within 10 mm of the crack tip. The COD is of the order of ten to one hundred micrometers, and is proposional to the square root of the distance from the crack tip. Dynamic fracture toughness K_ID is calculated through the formula of COD in the singular stress field of a propagating crack.

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Surface cracks can be detected by using an infrared radiation sensor. In the present study, a surface crack detection method by using the infrared radiometer was applied to a test plate with artificial cracks. The cracks could be detected with the higher equivalent radiation temperature at the crack than that of the flat surface. The minimum crack, 40 μm in width and 10 μm in depth, could be detected by using the present infrared radiation sensor.

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The surface crack detection method by using the infrared radiation sensor was proposed in previous studies. In the present study, the method was applied to metallic and ceramic plates with small slit-type artificial cracks. The crack width is small as the wave length of the detected infrared ray (8-13 μm). It is found that even hair crack of the ceramic plate with the width of 5 μm can be detected by the infrared radiation sensor.

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Following a Mindlin's theory for the bending of thin plates, we consider the electromagnetoelastic problem of a conducting plate containing a through crack under a uniform electric current flow and a constant magnetic field. The current flow is disturbed by the presence of the crack and the twisting moment is caused by the interaction between the magnetic field and the distubed current. Fourier transforms are used to reduce the electromagnetoelastic problem to one involving the numerical solution of a pair of coupled integral equations. The problem concerning the electric current density field is solved exactly. The singular stresses near the crack tip are determined in closed form. Numerical results on the moment intensity factor and the shear force intensity factor are obtained and are presented in a graphical form.

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The Saint-Venant torsion problems of involute serration shafts (JISB 1602), and involute spline shafts (JISD 2001) are treated. Stress concentration and rigidity of solid shafts and hollow shafts are analyzed by the indirect fictitious-boundary integral method.

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A solution is presented to a doubly mixed boundary-value problem of the torsion of an elastic layer by a circular rigid punch attached to its surface. The lower face of the layer is assumed to be clamped to the rigid foundation weakened by a cylindrical hole coaxial with the punch. The problem is reduced to a solution of infinite systems of simultaneous equations in which both the displacement on the lower face of the layer and the contact stress under the punch are expressed as appropriate series. Numerical results are obtained showing the effect of the hole and the thickness of the layer on the torsional deformation and the stress field The disturbances due to the presence of the hole are also presented in curves calculated numerically, and comparisons are made with results in the absence of the hole.

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This paper deals with a two-dimensional stress analysis of butt adhesive joints with a circular hole defect in an adhesive subjected to external bending moments. Assuming that adherends are rigid and replacing an adhesive with a finite strip including a hole defect, the analysis is done using the two-dimensional theory of elasticity in order to examine the strength of joints. The effects of the location and size of a hole defect on the stress distributions around the hole and at the interfaces are shown by numerical computations. For verification, photoelastic experiments are performed. The analytical result is in fairly good agreement with the experimental result. As a result, it is seen that the principal stress around a hole becomes larger with an amount of shift to the free boundary and it is seen that the stress concentration becomes larger with an increase of the size of a hole.

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The present paper proposes variational principles in finite deformation for a metal alloy showing predominant plastic flow or nearly incompressible material in elastic range, in order to improve the accuracy of numerical analysis. The variational theorems are presented in total Lagrangian formulation in terms of second Piola-Kirchhoff symmetric stress tensor, which can be easily reduced in an updated Lagrangian one. Attention is also focused on the unified derivation of mixed variational principles for residual work related to unbalanced forces which have not been studied previously.

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The rigid-plastic finite element method which is based on the upper bound theorem in plasticity is applied to the study of deformation behaviour of inhomogeneous materials with inclusions. The axisymmetric inclusion problem is studied in the present paper. The penalty method and the Newton-Raphson's repeated calculation is adopted to minimize a functional and to obtain the solution. Characteristics of the deformation behaviour of inhogeneous material are discussed based on the calculated results. The effects of the aspect ratio, the volume fraction and the yield stress ratio of inclusions on the deformation behaviour are investigated. The mean yield stress of inhomogeneous material is estimated based on microscopic deformation in the inclusion and the matrix.

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Large elastic-plastic deformation in, for example, metal working processes has been analyzed so far primarily on the basis of J 2 D, especially when the strain localization such as shear-band formation would take place in the material. However, J 2 D includes some ambiguity in loading-unloading judgement. The MG-constitutive equation was previously proposed by the author to recover such faults of J 2 D. MG c. e. has a difficulty such that it leads a nonlinear stiffness equation in the finite element method (FEM) . In this paper, two revised forms of MG c. e. are proposed which are readily introduced into the existing computer programs of FEM based on J 2 D or J 2 F. It is demonstrated by some basic large deformation analyses that the revised MG c. e. 's give very similar results as those based on the original MG c. e. or to each other.

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A constitutive equation with a one-to-one relation between the stress rate and the viscoplastic strain rate is generalized to describe the deformation behavior of temperature-dependent materials. This constitutive equation and work done by the viscoplastic deformation were introduced to the finite element program and then applied to the solution of deformation behaviors of strain rate and temperature sensitive blocks subjected to tension. The effect of the deformation velocity, material strain rate, temperature sensitivities and thermal conductivity on the flow localization has been clarified.

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An analytical method to simulate the temperature and the stress fields in a continuous casting slab under steady operating conditions is presented. The heat conduction equation incorporating heat generation due to solidification was solved by finite element method to obtain the spatially steady temperature distribution when considering material flow. Elastic-plastic stresses in the solidified shell were also evaluated. A parameter study was carried out in order to obtain the optimal operating condition such as shell thickness, site of crater end, and stress distribution as functions of the casting speed and cooling condition.

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An approach to describe the yield-point phenomenon of carbon steel at a low strain rate was presented by considering the behavior of the moving dislocations in the resisting force field of the random barriers theory. By reflecting the catastrophic increase of movable dislocations freed from any locking atmospheres in the internal structure variable on the theory, the equations to express the stress decrement at the upper yield point and the yield-point elongation were derived. Through the examination of the test results for several annealed carbon steels, it was clarified that the upper and lower yield point as well as the yield-point elongation of these metals could be described systematically with the area fraction of pearlite in a ferrite matrix.

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Three-dimensional impulsive stresses are analyzed by the boundary element method with the Laplace transformation and the numerical inversion using the fast Fourier transformation. The accuracy of the numerical integral in the non diagonal terms of the coefficient matrices obtained from the discreteness of the boundary integral equations are maintained well for the series expansion of the foundamental solutions. As a result, the stresses on the boundary given for the numerical tangential derivatives of the surface displacements and the surface forces are accurately obtained. The singularities do not occur in the dynamic terms, and this procedure is expected to be used only in the calculation of the static terms. As an example of this method, the procedure used to obtain the dynamic stress concentration factors of the cylindrical bar having the hemicircular notch are shown.

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Vehicle collision characteristics are among the most important characteristics to be examined in the design stage. These characteristics are dependent on the collapse mode of the box columns making up the side members of the body. An accordion-type collapse mode in which the columns do not bend but collapse in sequence is most ideal. Beads or reinforcements are often used to produce this kind of mode; however, investigation conducted on them has been mainly through experiments due to an absence of adequate analytical methods such as FEM. In this study, we show that, using a mathematically improved FEM along with a supercomputer, precise crush analysis can be conducted on columns or columns with some beads when the first buckling mode is provided as initial deflection.

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A self-adaptive mesh refinement technique is developed for boundary element analyses of two-dimensional elastic problems. This method is based on acquiring the desired accuracy for each element. From the numerical experiments for uniform mesh division, the relation ξ^αh^β is deduced, where ξ is the integral of the squared absolute error of displacement or traction along the boundary, and h is the mesh diameter. Applying this relation to two results for different mesh diameters, the number of a third division is decided. A computer program using this self-adaptive mesh refinement technique is developed and applied to several problems involving various shapes by the constant or quadratic element. The usefulness of this refinement technique is illustrated by the application results.

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In order to perform an accurate stress analysis in the framework of photoelasticity with computer-aided image processing, it is desireble to obtain the difference of the principal stresses and their directions over the whole area of the model, comparing the calculated result with the experimental data visually in each step of processing. The authors, in this paper, would like to focus on the classical photoelastic method with a plane polariscope. The subjects discussed are as follows : 1) to devise an explicit description of an equation for the direction angle of the principal stresses, analyzing the structural equation of the intensity of light in a plane polariscope, 2) to establish an algorithm for the calculation of the principal-stress direction over the whole area of the model, 3) to verify the effectiveness of the algorithm through various applications with experimantal data, 4) to present a method for more accurate and reliable separation of isochromatic fringes from isoclinic fringes, and, finally, 5) to propose a new method for computer-aided photoelastic analysis which can utilize a limited number of isoclinic patterns.

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In this paper, two-dimensional transient thermal stresses in a plate due to a zonal heat source moving back and forth with a constant angular velocity along its plane boundary are theoretically analyzed with consideration to convective heat loss across both plane boundaries. Numerical calculations of the temperature and the thermal stresses are carried out for various combinations of heating conditions, and the results are expressed in figures.

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Two-dimensional steady thermal stress without heat sources can be easily obtained by means of the boundary element method. However, if there are point or line heat sources within the region, it is difficult to solve these problem. This paper discribes a numerical method to solve the two-dimensional steady thermal stress under point and line heat generation. The temperature distribution can be obtained by the indricect boundary element method. The thermal stress is analyzed by means of the thermal displacement potential, the boundary element method and the method of superposition.

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Parametric study on the thermal deformation and the thermal stress of a resin molded package LSI has been performed by the boundary element analysis code, specially developed for this study. The length and the position of the Si chip in the LSI package are employed as the parameters in this study. Boundary element analysis of heat conduction and thermal stresses in a steady-state is carried out under the uniform temperature condition and the heat-generating condition with the heated chip. It is found that the position to minimize the package deformation is located just below the center of the package, however the stress concentration near the Si chip corner becomes nearly maximum on that position of the chip under both conditions. In the heated chip case, both the thermal stress near the chip corner and the package deformation increase as the chip length becomes large.

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In this paper, we propose a method of analysis for some inverse problems in elastodynamics. The inverse problem under consideration is defined such that the shape and location of an internal defect in a structural component are not known, but the displacements on some part of the boundary are given as additional information. The integral equations are derived in terms of the modification for an assumed defect shape from the well-known integral equations for elastodynamic problems by a Taylor series expansion. The boundary element method is then applied to the numerical implementation of the resulting boundary integral equations. The computer program is developed for two-dimensional problems. The effectiveness of this method is revealed through numerical computation for a couple of sample problems.

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The numerical analysis of the elasto/visco-plastic dynamic response of the general thin shells to arbitrary loads is carried out by the use of the elasto/visco-plastic overlay model which is able to express the Bauschinger effect and the strain rate dependence. Namely Perzyna's equation is used for the constitutive relation of each layer of the overlay model and as a whole the Bauschinger effect and the influence of viscosity in the plastic range of the material are taken into account. The equations of motion derived from the Sanders nonlinear theory for thin shells by adding the inertia terms are used, and the relations between strains and displacements where rotations of the shell are considered for the membrane strains are employed. The equations are numerically solved by the finite difference method. As a numerical example a cylindrical shell under a semisinusoidal external load with respect to time is analyzed and the results are compared with those in the case of isotropic hardening.

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By applying Love's equilibrium equations, the forces and bending moments in slot rods of an optical fiber cable have been determined. The deformation of the slot rod subjected to the forces and bending moments just derived has been analyzed by means of the three-dimensional finite element method. The results for the cable with 600 optical fibers showed that the deformation of the slot was so small that the clearance between the fiber tapes and the lateral wall of the slot was sufficient when the cable was subjected to the extentional strain of 0.1 % and the curvature due to bending was not larger than 1/1100 1/mm.

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