A study has been conducted to make clear the relation between the critical size of inclusion and the length of non-propagating crack and to evaluate the true fatigue limit of inclusion free microstructure and then compare it with the conventional fatigue limit of high strength steels. The results are summarized as follows ; (1) There exists a critical size of semi-spherical surface flaw beyond which the surface flaw has an effect of reducing the fatigue strength of steels. Such a critical size (d_c) of surface flaw is nearly equal to the length of non-propagating crack in the quenched and tempered steel at medium hardness level. (2) True fatigue limit estimated for the inclusion free microstructures increases linearly with the hardness of microstructure even in the hardness level over the optimum hardness H_<v, c<. (3) The fatigue limit of ultra low oxide spring steel containing Al₂O₃ inclusions of 20 μm diameter is estimated to be about 80 % of the true fatigue limit of the ideal inclusion free steel at the same hardness level.

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Rotating bending fatigue tests and the measurement of inclusion size distribution using the quantitative metallography technique were carried out on a quenched and tempered SAE9254 steel, and discussions were made on the relationship among the fatigue limit, inclusion size and toughness. Results showed that the high fatigue limit over 1000 MPa is easily obtained when the induction-hardened SAE9254 steel is tempered at the temperature just below the temper brittleness zone, indicating that such a condition of tempering gives the combination of hardness and toughness preferable for high fatigue resistance. Existence of an inclusion having maximum size (∼30 μm in dia. for present material) below the specimen surface is a primary cause for the occurrence of subsurface fracture associated with a fish eye on the fatigue fracture surface. The role of the inclusion with extraordinarily large size in the fatigue behavior of high-strength steel has also been discussed on the basis of the results of the fatigue test of the specimen having a surface micropit artificially introduced to simulate a surface inclusion.

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Rotating bending fatigue tests of plain specimens with a small blind hole were carried out in order to evaluate the effect of oil viscosity on the fatigue limit and small-crack growth law, under the environments of four kinds of base oils. In the present experiments, although the effect of the oils on the fatigue limit is hardly observed, the small-crack growth law, dl/dN=C₁σ_aⁿl, is affected by the viscosity. That is, the value of n tends to increase with an increase in the viscosity ; n <cong>8 in air, n <cong>10 in lower-viscosity oils and n <cong>11 in higher-viscosity oils.

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The accurate measurement of the flexural modulus of composite sheet materials is essential in the analysis of composite structures subject to bending loads. The bending of thin symmetric sandwich laminate plates is characterized by a matrix containing four independent terms. In the past, little attention has been given to the direct measurement of these terms. In the present paper, a new method is devised for loading a uniform bending moment or a uniform twisting moment to a symmetric sandwich laminate plate. Holographic interferometry was used as a means of determining the curvatures in a thin orthotropic sheet. The flexural modulus is obtained from the moment-curvature relation. Finally, the experimental result of the deformed shape for another loading condition is compared with the result of FEM using flexural stiffness terms derived from our experiment. Both results have a good agreement. Direct measurement could be the only practical means of accurately deriving the flexural stiffness terms.

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Measurements of the velocities of ultrasonic transverse waves were performed to investigate the development of elastic anisotropy of a polycrystalline metal with plastic deformation. From the same bar of steel S18C, specimens were so prepared that the velocities υ₁ and υ₂ of two polarized transverse waves could be measured for several propagation directions in a series of states deformed plastically by uni-axial compression along the bar axis. The results show that the anisotropy of the material is composed of an initial transversc isotropy, and a transverse isotropy developed in proportion to the plastic compressive strain ; these are slightly different in type, and opposite in sign. The latter transverse isotropy is also shown to be similar to that expected by the Voigt model of a polycrystalline aggregate.

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The boundary element method (BEM) has been used in various fields because it is convenient in comparison with FEM. BEM does not need a volume integral in three-dimensional elastic problems without body forces, but generally in unsteady three-dimensional thermoelastic problems, the volume integral is necessary. Recently, a method transforming the volume integral in BEM for three-dimensional problems of unsteady thermoelasticity has been reported. However, the time integral was not carried out analytically and a numerical example was not shown in that report. This paper describes the three-dimensional problem of unsteady thermoelasticity can be easily solved without a volume integral by means of a thermoelasticity displacement potential and the boundary element method. It is also shown that the time integral can be carried out analytically and a singularity problem caused by imposing virtual heat sources on the boundary element can be easily solved. Some numerical examples are shown for investigating the accuracy of this method.

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The thermoelastoplastic stresses caused near the circumferential boundary of the water cooling zone are dynamically simulated by FEM in a model with a large-scaled low-alloy steel shaft material. In this analysis, the incremental strain theory and the Mises' condition with a yield definition are used. In the beginning of cooling from the austenite zone, a notable tensile stress concentration area caused by plastic strain with a high equivalent stress grows near the cooling boundary. According to the growth of the transformation zone, in the applied area, the tensile stress changes for the compressed gradually. As the result, high compression stress concentrations appear within residual stress distributions.

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A one-dimensional generalized thermoelasticity is presented based on Lord and Shulman's Theory which involves one relaxation time of the thermoelastic process. This theory has been developed in an attempt to eliminate the paradox of an infinite velocity of thermoelastic propagation inherent in the classical one. The analytical object of this paper is an infinite body with a circular cylindrical hole. The boundary condition is that a constant heat flux is flowing into the infinite body so that the displacement at a circular cylindrical hole is constrained. An approximate analysis for short times is carried out because it is very difficult to obtain an exact solution. The numerical results of the effect of the relaxation time on displacement, temperature and stress distributions are shown.

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Transient thermal stresses are investigated in a transversely isotropic finite circular cylinder inserted into a rigid heated circular ring. The temperature and thermal stress fields are analyzed by means of the Laplace transform and the transversely isotropic potential functions method, respectively. The radial, hoop and axial thermal stresses have singularities at the end of the contacted rigid ring on the cylindrical surface. For that, factors are defined to evaluate the singularities of these stresses. Numerical calculations of these factors were carried out for transversely isotropic graphite. The effects of transverse isotropy, Biot numbers and the length of the circular cylinder on the factors are examined.

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In a previous paper, in order to improve the accuracy in BEM and FEM, we proposed an expedient method based on the similarity of stress fields near notch roots. In this paper, this method is applied to some three-dimensional BEM problems using constant elements, and its effectiveness is shown. This method enables us to analyze three-dimensional stress concentration problems by coarse meshes.

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The isothermal elastic and the thermo-elastic problems of an infinitely wide plate with a single edge crack are examined. In the isothermal elastic problem, we assume the crack surfaces are subjected to an arbitrary pressure distribution which is the same at corresponding points on the opposite surfaces of the crack. The crack problem with mixed boundary conditions is reduced to that required to solve dual integral equations. As a result, we have obtained the engineering data with high accuracy over a wide range of the ratio b/a (b;crack length, a;plate thickness). In the thermoelastic problem, the transient behavior of the thermal stress intensity factor is considered in case the edge-cracked plate is cooled down from high tempera-ture by the surrounding medium.

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The discontinuous model is a model in which the discontinuities inside of the continuum are taking into consideration. In this paper, we try to apply the discontinuous model to crack problems and investigate its applicability through the analyses of the specialized case of this model ; that is elastic-plastic crack models in which the continuous distribution of dislocations are assumed. The contents are as follows ; (1) In order to correspond with the Dugdale and BCS models and inclined strip yield model a constitutive relation of discontinuous plane is devised. (2) Finite element analyses of discontinuous model corresponding with these models are carried out, and an applicability of this model to analyses of crack model with dislocation arrays are confirmed.

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The discontinuous model is a model in which the discontinuities inside the continuum are taken into consideration. We showed, in the first report, that this model can be specialized so as to correspond with the elastic-plastic crack models in which the continuous distribution of dislocations is assumed. In this paper, the finite element formulation for the discontinuous plane using isoparametric elements is presented, and we show that we can treat more generalized dislocation models by applying a general constitutive equation to the discontinuous plane. Further, various kinds of elastic-plastic crack models by introducing the discontinuous planes are discussed, and, through the corresponding finite element analyses, their applicability is considered.

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This study investigates the problem of applying fracture mechanics to the evaluation of strength of adhesive joints. Double-cantilever beam (DCB) and single-lap joint (SLJ) specimens with a crack in their adhesive layers are employed for this study. The adherends are acryl and epoxy plates and the adhesive is cemedine 1500. The energy release rate G for a crack in an adhesive layer is analyzed by a finite element method and also by a compliance method. It is necessary to evaluate the mode I and II energy release rates separately. For this purpose, a virtual crack extension method (VCM) is successfully applied to FEM analyses for a mixed mode crack in the adhesive joint. The results obtained by FEM combined with VCM coincide with those obtained experimentally by a compliance method. The fracture toughness of DCB and SLJ adhesive specimens is well characterized by the energy release rate. It is found that the mode I energy release rates G_IC for both the DCB and SLJ specimens agree with each other and it seems that the mode II energy release rate G_II has a very small effect on fracture toughness.

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When a link chain consisting of steel rings with the link pitch of 15∼25 mm was subjected to a constant tensile velocity at its one end, the load produced corresponding to the velocity was measured by means of strain gages. The load measured was studied on the basis of a one-dimensional theory of stress wave propagation. As a result, it was found that the above theory is available to determine the load if the chain is replaced by an equivalent rod ; that is, the load is proportional to the velocity, and the proportionality constant is determined by the link pitch, the weight per unit link and the slope of the load-strain relation of the chain under static tension. Further, the case for a chain struck by a drop weight was also studied. It was shown that the upper limit of the maximum load produced is expressed by the ratio of the weight of the striking body to that of the chain.

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In the present report, the principle of structural analysis by the ε-method was treated theoretically for two-dimensional multi-storied and multi-span rectangular rigid frames loaded vertically or horizontally, in cases where each member of the rigid frames had rigid zone at both ends and the bases of columns were connected by footing beams. A digital computing program for the structural analysis of the rigid frames was constructed on the basis of the ε-method and various quantities were computed by this program. The ε-method, named by the authors, is one of the slope-deflection method and is of practical use in the structural analysis of rigid frame. Finally the results calculated by the digital computing program are shown in several figures in the present paper.

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In this paper, the most general higher-order equations of three-dimensional static and dynamic theories for a circular cylindrical shell are derived by expanding the displacements into an infinite power series with respect to the radial coordinate of the shell. The present formulation can be taken into account acctually any higher-order terms for both cases of static and dynamic problems. Several theories which were proposed previously, can be deduced by the employment of the lower-order terms in our theory. Three typical theories such as 3-order theory, Levinson-type theory and Levinson-Voyiadjis-Baluch-type theory are also newly derived from the present formulation. Numerical results of natural frequencies for simply-supported cylindrical shells are compared to the exact solution as well as many theories.

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It is well known that braiding construction is a useful reinforcement configuration in three dimensional composite. We previously presented simulation techniques for the basic flat and cord braiding mechanisms, and discussed the relationship between braiding construction and fabricating condition. However, it is difficult to fabricate the braiding construction with a complex cross section using the usual braided machine. In this paper, we propose a new braiding mechanism for fabrication of three dimensional braiding construction in which the orbit of the bobbin on the plane has no limitations. We also clarify the feasibility of this braiding mechanism.

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In the reliability-based design of machines and structures, it is important to provide distribution characteristics of the mechanical properties of each member together with the frequency distribution of the applied load. In this study, mechanical properties of tensile strength σ_B, upper yield stress σ_SU, lower yield stress σ_SL, elongation δ, area reduction φ, Vickers hardness H_V and impact energy E were examined by using fifty specimens of S35C carbon steel, which were machined from two bars supplied as the same charged and the same heat-treated material. Distribution characteristics of these properties were discussed, and the correlation between each pair was also investigated from the statistical viewpoint. The main conclusions obtained are summarized as follows : Distribution characteristics of σ_SL, σ_B, δ, φ, H_V and E are well approximated by a normal distribution, but those of σ_SU are not approximated so well by this type of distribution. In such a case, a Weibull distribution is preferable to represent the distribution pattern. No significant correlation was observed between each pair of the above mechanical properties. Consequently, the individual property has the inherent distribution characteristics independent of the other properties.

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Transducers consisting of a strain gage or accelerometer and piezo-electric sensor are popular instruments used to evaluate dynamic response. Although the observation of transmitted strain by means of the strain gage method assures accuracy, it is not convenient to estimate the dynamic response of materials having a large cross-sectional area. On the other hand, there is little restriction in measuring of dynamic response using an accelerometer since it is small and light. It is easy to fabricate the transducer by applying a piezo-electric sensor. However, except for the strain gage method, the technological issues as to whether these are consistent or accurate for the measurements of dynamic response, particularly the impact load, have not been apparent. In this paper, we distinguish the technological issues which may arise in using such dynamic response transducers for measuring the impact load caused by the collision of two round bars or a sphere and flat plate.

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Erosion data of many targets proposed by researchers may not be considered as having immutable values because these data depend on the properties of test facilities, particle characteristics and particle distribution. To treat erosion, we must first eliminate the particle distribution effect from the erosion and evaluate the erosion using one particle. Therefore, a formula for the calculation of erosion using one particle with erosion tests for a particle having log-normal size distribution is proposed. Erosion using one particle based on the unity particle diameter is calculated by particles which are of the same material, but having different diameter distribution. Good accuracy for erosion is obtained evaluation with the formula using one particle estimation.

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