Fatigue tests of 0.31% carbon steel specimens with a circumferential groove were made in a wide range of configuration parameters. As a result, it has been confirmed that the linear notch mechanics (LNM) can be successfully applied to the examination of notch effects in fatigue. Master curves useful for the estimation of notch effects in carbon steels were also produced by arranging previous data, based on the LNM. Moreover, the fatigue limit of specimens with a drilled hole was discussed by using the LNM.

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The fatigue threshold stress intensity factor ΔK_th, based on dislocation dynamics was formulated as a simple function of temperature and grain size. This theory shows ΔK_th decreases as temperature increases, and corresponds well with the experimental data for steel under not so high temperature. This theory also corresponds well with the surface roughness effect on ΔK_th. Furthermore, the mechanical characteristics of the dislocation free zone. The dislocation free zone corresponds well with the mechanical characteristics of ΔK_th.

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The high-temperature fatigue crack growth rate and progressive damage region around the crack tip were investigated for the range of f=1 Hz0.001 7 Hz under a vacuum condition (1.3 MPa) and 650°C using SUS 304 stainless steel. A creep test was also carried out under the same conditions. From these experimental results, the fatigue crack growth mechanism is found to be different from the creep crack growth mechanism by the observation of the frequency characteristics and the behavior of the progressive damage region. The stress increasing and decreasing processes for fatigue crack growth do not saturate the stress holding process for creep crack growth even though the stress increasing and decreasing rates decreases. The crack growth rate is found to be controlled by the progressive damage rjgion around the crack tip.

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A stochastic model and a method of simulation of the initiation and the early propagation of creep-fatigue small cracks along grain boundaries were proposed. In the model, grain boundaries between two adjacent triple points were projected and linked on a straight line perpendicular to the applied stress axis, and their length was given as random variables of a normal distribution. The grain boundaries had their own fracture resistances, the magnitudes of which were given as uniform random numbers. The fracture resistance of each grain boundary decreased by a constant magnitude corresponding to the driving force of one fatigue cycle. When the resistance become zero or a negative value, the grain boundary was assumed to fracture and to yield an intergranular facet of small crack. Based on this model, a numerical calculation was done for a smooth specimen of 304 stainless steel subjected to the slow-fast strain cycle of 1%-total strain range at 923K in a vacuum. The result of simulation on crack density, cumulative probability of crack length, and crack propagation rates coincided with the experimental results.

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The effect of grain-boundary reaction precipitates on the high-temperature fatigue crack growth was investigated using austenitic 21 Cr-4Ni-9Mn steel at 937K in air. Grain boundaries were serrated by the grain-boundary reaction precipitates. The crack-growth rate was considerably decreased by these precipitates, especially under the condition of a low crack-growth rate. The fatigue cracks extended on the serrated grain boundary or on the interface between the grain-boundary reaction nodule and the grain. Therefore, the cracks grew on the zigzag paths, and brittle intergranular fracture was then retarded. The retardation of the fatigue crack growth was explained by these changes in fracture mode.

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Surface crack growth under rotary bending, where a stress gradient is produced in the cross section of the specimen, was analyzed in terms of the stress intensity factor range, ΔK, and the cyclic J-integral range, ΔJ. These data were compared with those of a large through crack in a center-cracked specimen and a short surface crack in a smooth specimen under a push-pull load. The surface crack growth rate plotted against ΔJ in the rotary bending test was nearly coincident with those for the short surface crack and the large center crack under the push-pull load. The stress intensity factor, which was analyzed for a crack in a semi-infinite body by Raju-Newman, could be applied to the analysis of the fatigue crack growth of the laboratory-type specimen in a practical sense.

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A deterministic approach is proposed for the identification of heat-source or force applied in a domain from values of integrals evaluated on the boundary. For steady-state heat conduction problems, it is shown that a volume integral of the intensity of a heat-source multiplied by a harmonic function can be expressed by a boundary integral. This enables us to determine the intensity and the location of the heat-source by combining the values of the boundary integrals evaluated using several harmonic functions. This approach is extended to the identification of the heat-source for transient heat conduction problems. It is shown that the method can be further generalized for the determination of input in a system governed by a linear partial differential equation. The usefulness of the proposed method is demonstrated by a numerical simulation of heat-source identification for a steady-state heat conduction problem.

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This paper deals with the stress concentration problem of a circular solid cylinder with a form of a test piece specimen subjected to torsion by a pair of rigid chuchs. A method of solution is developed for the problem by using Green's functions for torsional body force problems of an infinite thick plate. The method of solution is said to be a kind of the so-called body force method, charge simulation method, indirect boundary element method with fictitious boundaries and so on. Numerical results are shown systematically for various sizes of the solid cylinder. Considerations are made for the influences of the radii at the stepped parts and sizes of the solid cylinder on the stress concentration factors and on the positions where the maximum stress appears. The convergency of solutions by the present method is also investigated.

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In the present paper, we show the new analytical method of the three-dimensional elastic problems in finite deformations with body force. By applying Hasegawa's presentation and Adkins perturbation method, we propose the analytical method for axisymmetrical dynamic problems with body force by using displacement functions. These displacement functions are obtained from Green's function, and further, the stresses and displacements are introduced from these functions. Finally, this analytical method is examined by a simple example.

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This paper is concerned with the torsional impact response of an infinite medium with a flat annular crack around an infinitely long cylinder with different elastic constants. Laplace and Hankel transforms are used to reduce the problem to the solution of a set of triple integral equations in the Laplace transform domain. These equations are solved by using an integral transform technique and the result is expressed in terms of a singular integral equation of the first kind. The dynamic stress intensity factor is obtained numerically, and the effects of the geometrical configulations and the material properties of the composite material on the dynamic stress intensity factor are shown graphically. Two limiting cases, in which the surface of the cylindrical cavity is stress free and is fixed, are included.

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This paper describes a new data smoothing technique based on a modified least-squares method using finite elements. To smoothly interpolate discrete data, least-squares methods combined with a polynomial or the spline function are commonly used. However, these methods often cause oscillations in the approximation functions and are not so appropriate to calculate derivatives of those function. In order to avoid such oscillations, we propose a new data smoothing technique using finite elements, where the Sobolev norm is minimized. This method takes into account not only the smoothness of the data but also that of the first-order derivative. The present method is applied to one-dimensional as well as two-dimensional problems, and its accuracy and convergency are demonstrated.

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Errors inclued in solutions of the boundary element method are caused by discretizing the boundary of analysed objects into many elements. In the present paper, the erron tendencies are discussed in order to have reasonable usage of the boundary element method in 2-D elastostatics. The main results are the following : (1) Solution error rates obtained by BEM depend on the boundary condition. However, the absolute values of the displacement error rates under traction conditions are equal to those of the traction error rates under the given displacement condition with different signs at some conditions. (2) In-plane bending cannot be practically solved by the constant or linear element discretization. Quadratic element discretization can give us a satisfactory solution for almost all objects. (3) The solution errors depend on Poisson's ratio before the solution converges.

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High bending stresses are applied to the shell-to-annular joint of a cylindrical storage tank due to seismic loading, and the stress concentration occurs at the toe of a fillet weld. During the operation, flaws relating to welding or corrosion in this region will become surface cracks. This paper describes the stress intensity factor analysis for surface cracks at the shell-to annular joint by the influence function method. The stresses on the virtual crack surface of the uncracked tank under seismic loading are calculated by the coupling method of finite and boundary elements.

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As a basic study for the establishment of an accuracy estimation method in the structural analysis using the zooming method, this third report deals with the problems of two dimensional elastostatic stress analysis by the finite element method. From numerical experiments, the following relation was deduced, ε∝ (h/a)^k, k>1, where ε is the error of the value by the finite element method relative to the exact value and h/a is the dimensionless mesh diameter. Using this relation, the errors of displacement on zooming boundary and that of stress at the selected points in the zooming region can be estimated by the recursive analyses of the whole region or of the zooming region. The error of stress at the selected points is expected to be smaller than the sum of these errors. A computer program using this error estimation method was developed and applied to several problems of various shapes. The usefulness of this accuracy estimation method was illustrated by these application results.

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The 25% side-grooved CCT (center-cracked tension) specimens were analyzed elastic-plastically by using the three-dimensional finite element method. The models used in analyses were CCT specimens which were of two thicknesses (B₀=18, 4 mm) and 50mm width. The material was the general rolled steel (for structure ). In the case of an 18mm-thick CCT specimen employing [numerical formula]as the effective thickness, the load vs displacement curve of specimen with side-grooves is higher by about 6% than that of a specimen without side-grooves. In the case of a 4mm-thick specimen, the former is higher by about 11% than the latter. The effective of the side-groove is greater on a 4mm-thick specimen than on an 18mm-thick specimen. The J value estimated by Rice's formula using [numerical formula]as the effective thickness nearly coincides with the J value at the central part of the specimen with in about 6% error. It is possible to obtain valid J_IC by using the 25% side-grooved 4mm-thick specimen which dose not satisfy the HRR singularity.

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Crack energy density in an arbitrary direction ε_φ is expected to describe fracture behaviors of a mixed-mode crack. It was shown previously that ε_φ can be evaluated by a path independent integral with practically sufficient accuracy. In this paper, as an another evaluation method of ε_φ, a method based on the relationship between ε_φ and load-displasement curves is discussed. The contents are as follows ; 1) A relationship between initial crack lengths, load-displacement curves and ε_φ which holds until cracks start to grow is derived by considering the strain energies of the specimens with different initial crack lengths. A method to evaluate ε_φ from load-displacement curves is proposed based on this relationship. 2) Based on the method, the evaluation of ε_φ is tried from load-displacement curves obtained by finite element analyses and also experiments for specimens under tension with a crack inclined to the loading axis, and it is shown that the method is practical for evaluating ε_φ through the comparisons with the theoretical values and the values evaluated by the path-independent integral.

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The deformation and strength of adhesive shaft joints having shafts of the same metal and a coupling of various metals were investigated both analytically and experimentally. The strain distributions of joint under combined loads were analyzed by the finite element method. The strength of the joints was predicted by applying the strength laws to the adherend, adhesive layer and their interfaces. The effects of the coupling length and thickness on the joint strength were examined. The analytical strain distributions were in good agreement with the experimental ones. The results of strength prediction coincided approximately with the experimental ones. The effects of the Young's modulus of the coupling on the joint strength were examined by varying the coupling metals.

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The deformation and strength of adhesive shaft joints having shafts of dissimilar metal and a coupling of various metals was investigated both analytically and experimentally. The strain distributions of joints under combined loads were analyzed by the finite element method. The strength of joints was predicted by applying the strength criterion to the adherend, the adhesive layer and their interfaces. The analytical strain distributions were in good agreement with the experimental ones. The effects of the coupling length and thickness on the joint strength were examined. The effects of the Young's modulus of coupling on the joint strength were examined by varing the metals of coupling. The analytical results of strength coincided approximately with the experimental ones, so the joint strength could be successfully predicted by the strength criterion.

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In order to study the strength of the metal-FRP bounded joints, both of the finite element stress analyses and experiments have been carried out for T type bounded joints. It has been found that the fracture of the bonded joints, both the single lap joints and the T type joints, can be explained well by σ_max which is the maximum equivalent stress in the adhesive layer. The fracture occurs when σ_max reaches a critical value σ_f. σ_f is a constant for a specific bonded joint, and it can be estimated experimentally by the strength of a single lap joint. σ_max can be calculated efficiently by the developed stress analysis system. Therefore, the strength of the bonded joints can be estimated by the criterion, σ_max =σ_f, and the criterion is applicable to the structural design of the bonded joints.

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In the previous papers, the authors reported a new method for photoplasticity on cellulose acetate. This method made it possible to determine experimentally the values of stress and strain considering strain rate in the model. Therefore, in this paper the photoelasto plastic stress analysis of a strip with a hole under tension was carried out. The ratios of hole diameter to the gauge width in the plane models were chosen to be 0.1, 0.1 and 0.5. The head speed of the specimen was kept constant during loading. The distribution of stress and strain, the stress concentration factor in the elasto plastic region and the development of the plastic region were obtained taking rate effect into account. As a result, the stress on the smallest cross section increased as head speed increased. However, the distribution of strain, the spread of the plastic region and the stress concentration factor were not influenced.

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Peculiar stress-fields caused by surface flaws, as is well known, are exposed on the surface of engineering materiels under working loads. Few studies by applying thermoelastic effects whose thermograms are closely related to the isopachics on the surface have been made to estimate various surface flaws as a nondestructive testing, although the effects are generally employed to stress analysis in engineering structures. The authors have extended the thermoelastic techniques, therefore, to find nondestructively the semielliptical surface cracks with various axial ratios and inclination angles to the tensile axis, and have analyzed the isopachics over the surface using a finite element method to compare with the thermal image. As the result of the studies, it was verified that the dimensions of the surface cracks were successfully estimated through the temperature profiles of the thermograms.

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Braiding is the novel textile technology which promises improvements in properties of composite material and being to meet the requirements of automated fabrication. Our purpose is to clarify the mechanical properties of braided composites. In this paper, we discuss the tensile properties of the flat plate with flat blading construction. The tensile specimen is made from glass fibers and epoxy resin by hand lay up method. Two kinds of the specimens are also fabricated for comparison purposes : a specimen with a braided flat bar cutting the side edge and a specimen reinforced with plain woven cloth. It is shown in the tensile test that the strength of the braided flat bar is larger than that of the other specimens. This reason for this finding is that the transverse crack leading to fracture in the braided flat bar is not initiated from the side edge where reinforced fibers are continuously oriented. This compared with the other types of specimens which consist of cut fibers at the side edge.

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An optimum design technique of a stiffened plate structure which acheives minimum compliance is developed. The stiffened plate structure is discretized into the finite shell elements, and the minimum compliance problem of the stiffner height subjected to the volume is formulated. Introducing the design sensitivity analysis, an optimum distribution of stiffner height of the rectangular waffle plate supported at the corners which has stiffners of the latticework type is determined by the sequential quadratic programming technique.

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Fracture toughness tests of side-grooved specimens were carried out to investigate the equivalent thickness of a side-grooved specimen. The effects of side-groove on stretched zone width and stable crack growth were also investigated. From the results, the equivalent thickness for the J_IC-value will be in the range between B_e1(=B·B_N) and B_e2(=B-(B-B_N)²/B). Although the thickness B_e2 can be utilized from the viewpoint of conservative estimations, it is reasonable to use the thickness B_e1 which also gives good estimations for the blunting line.

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The onset of an unstable ductile fracture in a piping system is dependent on the compliance and supporting conditions of the loading system as well as the material properties. This paper firstly discusses the influence of the compliance and pipe support on the onset of an unstable fracture under bending load. Based on the bending test results of 6-inch and 12-inch diameter SUS304 pipes with a through-wall crack in the circumferential direction, an empirical expression which represents the critical instability condition of compliance and piping support is derived. Using the above expression, case studies are performed on the critical support span length for simply supported 3-point bending pipes of 3-, 6-, 12-, and 24-inch diameters. The calculated results show that the critical span length increases with the increase of pipe diameter and initial crack angle.

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Plane strain fracture toughness (K/<IC>) measurements were made on ceramics (graphite, engineering ceramics) using short bar and bend bar chevron notched specimens previously calculated by optimum specimen geometry, to enable precracking, by means of 3-dimensional finite element and Bluhm's slice model analysis. Acoustic emission (AE) signals were also measured for detecting precracking and successive crack growth. AE signals due to precracking and crack growth were obtained for all short bar and bend bar specimens of graphite ; and deviations of K_IC values were relatively small with variations in chevron notch angle and the width of the slot from 0.2 mm to 0.5 mm. In most engineering ceramics, unstable fracture immediately occurred after popin. About 20% higher K_IC values were obtained in comparison to another testing device (fractometer-Terratek Co.), except for one commercial hot-pressed Si₃N₄. It means that the width of the slot should be less than 0.2 mm in highly brittle solids, and confirmation of precracking is actually important to evaluate K_IC value.

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The plastic behavior of SUS 304 stainless steel is experimentally investigated at the low temperature of liquid nitrogen (77 K) under simple loading conditions as well as combined loading conditions. The loading tests are carried out by subjecting thin-walled tubular specimens of SUS 304 stainless steel to axial load and torsion. The compressive flow-stress is greater than tensile or torsional flow stress. The compressive flow-stress subsequent to tensile pre-strain is larger than the pure tensile flow-stress. This phenomenon is different from the Baushinger effect at room temperature. When strain paths subsequent to various pre-strain are bent with a corner, remarkable latent hardening exists in the subsequent plastic deformation.

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An analytical method for the elasto/visco-plastic dynamic problems of axisymmetrical thin shells subjected to mechanical and/or thermal loads is developed. The equations of motion and the relations between the strains and displacements are derived by extending Sanders' elastic shell theory. For the constitutive relations, the Perzyna elasto/visco-plastic equations including the temperature effect are employed. The fundamental equations derived are numerically solved by the finite difference method. As numerical examples, the simply supported cylindrical shells made of mild steel are treated and the following to cases are analyzed ; a nonuniform temperature cylinder subjected to impulsive internal pressure, and an internal pressure cylinder subjected to impulsive thermal load. In both cases the variations of displacements and internal forces with time are discussed.

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