Rotating bending fatigue tests were carried out for three metals; low carbon steel (S15C) with four grain sizes, pure copper and austenitic stainless steel (SUS 304). The distributions of crack initiation life N_i, growth life N_p and failure life N_f determined in this study were expressed as a two-parameter Weibull distribution. The statistical scatter of N_i, N_p and N_f distributions increased roughly with increases in grain size, except the smallest one and with decreases in stacking fault energy, and decreased with the development of fatigue cycles. The SUS304 showed the higest value of the correlation coefficient between N_i, N_p and N_f distributions during the whole process. The relationship between the coefficient of variation η of N_f distribution and the slope a of S-N curves was expressed as η =c(a)^-b, where b and c are constants.

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This study has been undertaken to produce a dual alloy gas turbine integral rotor composed of a precision cast Ni base superalloy bladed shell and a HIP consolidated Ni base superalloy core with a powder metal interlayer, Solid state diffusion bonding between solid metal and powder metal was investigated to bond both materials to each other. Prior to bonding, the solid metal was coated with Ni-electroplating, Au-electroplating and Ni ion plating. Compared with those coatings, including non-coating, Ni ion plating showed the highest mechanical integrity. Almost all failures in room temperature tensile tests and high temperature low cycle fatigue tests were located in the solid metal (casting or HIP consolidated metal). In stress rupture tests, several test pieces broke on the bond line. However, they showed almost the same rupture life as that of the solid metal.

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The effects of the overlap length on the strength of the adhesive scarf joint under bending were investigated analytically and experimentally. The scarf joints were constructed of glass cloth laminated plates (GFRP), carbon steel plates and epoxy resin. The stress distributions calculated by the finite element method nearly agreed with measured results. It was found that the stress distributions in the joints for long overlaps were large at the above end of the adhesive layer. The strength of the joints was estimated by applying strength laws of GFRP, carbon steel, the adhesive layer and their interfaces to the calculated stress distributions. It was shown that the joint strength depended on the interfacial strength for short overlaps, and on the strength of GFRP for long overlaps. When the strength of GFRP was the weakest of four parts, an initial fracture was observed on the specimen. The predicted results were in good agreement with the experjmental results.

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The bolt-bearing strengths of glass fiber reinforced composite laminates with four different stacking sequences were measured in this study. The effects of the stacking sequences on the failure mechanisms of the bolted joint were discussed. It was proved in this experiment that the initial failure load in the bearing load-displacement curve was adopted as the basic design data, and then the bearing strengths of the FRP with hybrid constitution could be predicted by applying the law of mixture.

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In the present paper, the stresses of butt adhesive joints are analyzed by a two-dimensional theory of elasticity in order to establish the fracture criteria when dissimilar adherends are bonded by an adhesive. Dissimilar adherends and an adhesive are replaced with finite strips, respectively, and the analyses are done as a three body contact problem. In numerical computations, the effects of the ratio of Young's modulus of dissimilar adherends, the ratio of Young's modulus of adherends to that of an adhesive and the thickness of the adhesives are shown on the distributions at the interfaces of the joints. As a result, it is seen that the principal stress becomes maximum at the interface between the adhesive and the adherend having high Young's modulus. For verification, experiments are performed. Analytical results are in fairly good agreement with experimental ones.

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The effect of a water environment on the near-threshold growth of delamination fatigue cracks was investigated with unidirectional laminates made from Ciba Geigy prepregs 914C (T300/914) and from Toray prepregs P305 (T300/#2500). Tests were carried out under mode I opening loading using double cantilever beam specimens. The crack growth rate was correlated to the equivalent stress intensity range without respect to the stress ratio. For 914C laminate, the crack growth rate in water was about one tenth of that in air in the power-law region. For P305 laminate, the effect of a water environment was small in the power-law region. Near the threshold, the crack grew slower in water than in air for both laminates. When the 914C laminate specimen was moisture-conditioned, the rate in water was about 300 times faster than that for the specimen in water without conditioning. These environmental effects were explained on the bases of fractography and fracture mechanisms.

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The plane strain fracture toughness, K_Ic, the fracture resistance, K_R, and the crack growth characteristics of stress corrosion c racking and fatigue were investigated for an alumina particulate filled epoxide composite. Based on the results, basic fracture characteristics were evaluated. The results obtained are summarized as follows: (1) The resistance to the stable crack growth as well as the fracture initiation is described as K=K_Ic. (2) Below K_Ic, stress corrosion cracking occurs. The threshold stress intensity, K_Iscc, is 0.89 K_Ic. (3) The threshold stress intensity for fatigue crack growth is smaller than K_Iscc. A marked influence of the stress ratio on the fatigue crack growth rates is observed. On the other hand, there is no effect of cyclic frequency. It is judged that interaction with stress corrosion cracking is not so significant.

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Supersaturated AI-10 at % Si solid solutions were prepared by using high pressure and high temperature techniques. The elastic constants, lattice parameters, electrical resistivity, density and hardness of these obtained specimens were measured by the process of isochronal and isothermal aging. For isochronal temperatures of about 100°C to 300°C, rapid changes of several characteristics were observed. In the aging process, the variations of elastic constants which had two stages appeared and the lattice parameters overshot those of pure-aluminum. The relation between the Al-matrix and the precipitated phase of silicon and the activation energies for precipitation are also discussed.

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Three dimensional transversely-isotropic bodies are analysed by the boundary element method with the analytical solution of Pan and Chou. The calculations are carried out for center through-crack and surface crack problems. The stress intensity factors of the cracks are obtained with fairly good accuracy. The results give an numerical assurance of the usefulness of the solution of Pan and Chou.

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Transient wave propagation parallel to elastic layers is studied on the basis of the approximate continuum theory. The wave front expansion method is introduced to analyze the wave behavior in the near-field where the wave changes its shape as it travels. The transient solution is derived and compared with an experimental result. It is found that the theory can predict all the important qualitative features of the transient wave, and also the quantitative agreement is sufficiently good.

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In order to estimate exactly the reliability of the service life of a pressure-proof connector made of polycrystalline alumina, static and cyclic fatigue of polycrystalline alumina and its brazing part were examined. Static and cyclic fatigue tests and also static bending tests under 4-point bending loads were carried out using three types of specimens : A ; plates, B : plates with a center hole and C : plates with a center hole brazed to Cu pin with Ag-Cu alloy. Fatigue failures of both A and B specimens were basically controlled by the static fatigue stress corrosion cracking, but in addition the effect of cyclic stress on their failures could be recognized from estimating the time to failure under cyclic stress based on the data in in static fatigue tests. On the other hand, fatigue failures of C specimens were mainly controlled by cyclic fatigue like metal fatigue. This is because the main mechanism of fatigue in C specimens is the initiation of fatigue crack in the brazing alloy.

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Completely reversed strain controlled low cycle fatigue properties at room temperature are investigated for structural carbon steels and weld metals. The weld metal specimens deposited by gas metal arc welding (GMAW) were taken from multi-pass weld metal such that gage length consisted entirely of the weld metal. The results indicate that there is a trend toward reductions in the low cycle fatigue life of weld metals as compared with the base metals. They are explained in terms of local plastic strain concentration by lack of uniformity of the multi-pass weld metals. The weld metals have not the same mechanical properties anywhere as confirmed by hardness distribution, and the fatigue crack grows preferentially through temper softening region of multi-pass welds. This study leads to the conclusion that fairly accurate estimates of the low cycle fatigue life of structural carbon steel weld metals are obtained by the results of base metals from the ratio of temper softening region. It is also confirmed by experiment that low cycle fatigue life of multi-pass welds can be improved significantly using half bead grinding technique and/or welding conditions.

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Fracture toughness tests were conducted on 2 CT plane size specimens (thickness t = 20 mm), prepared from carbon steel pipe STS 42 with circumferential TIG weldment (20 B, sch. 100), in ambient air. Some approximate expressions for J-Δa data are discussed from the view point of applicability to fracture analysis. The following conclusions are obtained. (1) Weld metal possesses higher resistance to stable crack growth and to unstable transition than base metal does. (2) The transition condition, from stable to unstable ductile crack growth, depends on the type of approximate expression of the J-R curve.

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Using a series of base oils of different viscosity grades, rotating bending fatigue tests of 0.34 % C steel plain specimens were carried out to examine the effect of oil environments on the fatigue behavior. Although the effect of oil is hardly observed in one grain size crack initiation process, its effect appears in the crack propagation process. As the main effects of oil, two actions are considered ; that is, the isolation of the atmosphere and the oil wedging action. The propagation of a crack smaller than 0.1mm is controlled mainly by the former effect. For a crack larger than 0.1mm, its behavior is controlled mainly by the latter effect. On the other hand, the effect of oil on the fatigue limit is very small.

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The growth behavior of a ductile crack resulting from a notch root was investigated in tensile tests of a center notched plate of low carbon steel S 15 CK. Four different notch root radii, ρ, that is, ρ=0.0 (crack), 0.08, 0.14 and 0.25 mm were prepared for testing. It was found by measurement of strain, e, and the notch shape in tension, that the notch root was blunting in the same way, independent of the notch root radius, before ductile crack initiation, The crack grew with mixed mode fracture which combined tensile mode and shear mode fracture. In the growth process of the ductile crack, the crack growth rate, da/dε, for the strain increment is proportional to crack length, a, and the proportional constants of the da/dε-a relation take nearly the same values independent of the notch root radius. The crack opening angle, COA, decreases with crack growth.

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An estimation method of long-term corrosion fatigue (CF) crack growth characteristics using laboratory data is proposed based upon a linear summation model in terms of modified effective stress intensity factor range, ΔK_cont, which eliminates the corrosion products-induced wedge effect. Long-term CF crack growth curves of a 50 kgf/mm² high-tensile strength steel, HT50 and HT50-TMCP, and a 80 kgf/mm² one, HT80, in synthetic sea water are estimated supposing that ΔK_cont is idential to nominal stress intensity factor range, ΔK. The threshold values for long-term CF, ΔK_CF, taken from these curves are nearly equal to the threshold values for crack initiation at corrosion pits, ΔK^*_<CF>, which are calcuated assuming the pits as sharp cracks.

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The effect of stress wave form, that is, fast-slow (t_R<t_D), slow-fast (t_R>t_D), symmetrical (t_R=t_D) wave form on corrosion fatigue crack growth rate was studied, where tR is rising time and t_D is descending time. When t_R is smaller than t_D+t_H, t_D is not so effective on crack growth rate and t_R is much more of a controlling factor. Where t_H is stress holding time, corrosion fatigue fracture toughness is constant independent of t_R, t_H and t_D, and takes the same value of that in air, while corrosion fatigue crack growth rate is remarkably effected by t_R and t_H. So, the effect of stress wave form motivates local corrosion dissolution at the crack tip and accelates crack growth rate, but does not affect material damage so much.

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This paper deals with stress concentration analyses of a 60'V-shaped single edge notch, 60'V-shaped double edge notches or partially-circular double edge notches in an infinite strip under transverse bending. The moment field induced by a moment in a semi-infinite plate is used to solve those problems. The results show that the Neuber formula gives underestimated stress concentration factors for the wide range of the notch depth. However, in the case of blunt notches, the Neuber solution of deep hyperbolic notches still gives sufficient accuracy in engineering use. In addition, the stress concentration factors of 60°V-shaped notches are also represented by diagrams.

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The three-dimensional axisymmetric elastic boundary value problem of the torus of a closed hollow circular cross section with varied thickness under uniform internal pressure is analyzed by the indirect fictitious boundary integral method. The configuration parameters are the radius of the torus, the mean meridional radius of the hollow circular cross section, the thickness, and the eccentricity between the outer and the inner circles of the cross section. Moreover, the leveling of the stresses in the hollow torus is investigated.

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This paper deals with an inverse problem analysis for a semi-infinite solid under normal compressive load. By the inverse analysis technique, the Gaussian quadrature formula is used to reduce the integral equation to a system of linear equations. Under the assumed compressive load area, the distributions of compressive loads are analyzed. Furthermore, by minimizing the square sum of compressive loads in the assumed area, the reasonable area and compressive load distributions are obtained.

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Fifteen fresh, intact lumber intervertebral joints (L 3-L 4 disc body unit) from spines were loaded in an Instron type universal materials testing machine to determine their mechanical properties and internal disc pressure. Internal disc pressure was measured by a needle-type semiconductor pressure sensor. The measurements made included vertical load deformation and disc bulge in the anterior, lateral and posterior. The results showed that vertical deformation averaged 2.06 mm, and internal disc pressure was 0.52 MPa at 1000N : but internal disc pressure could not be measured in old aged samples.

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When a stepped beam is impacted, time histories of bending strain are measured by strain gauges which are cemented at the fixed end and the corner of discontinuity in the beam. Although the variations of bending strain calculated by the finite element method based on Bernoulli-Euler beam theory also involve the high frequency modes, those by experiment consist of the basic frequency mode and a few low frequency modes. Since the fixed end of a canti-lever beam in an experiment is not perfectly rigid, the periodicity of vibration is affected by it. The time histories of bending strain on the shelf of discontinuity differ from the flexural motion by the simpler Bernoulli-Euler theory. However, observing the variations of bending strain at the other location, except for the high frequency modes, the vibration of both is in fair agreement.

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The path independent T^* integral is valid for any constitutive relations under quasi-static as well as dynamic conditions. The T^* integral can be considered to be a natural extension of the so-called (Rice's static) J integral and the dynamic J integral (J'). Thus, the T^* integral is now recognized as a unified crack-tip parameter governing nonlinear as well as dynamic fracture. In this paper, the invariance of the T^* integral with respect to the shape of the fracture process zone was verified. To this end, the simulation of elastoplastic dynamic crack propagation was carried out by using a viscoplastic finite element method. Some other relations between the T^* integral and the process zone are included.

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Finite element analyses are performed on the assumption of the power-law hardening and the deformation theory of plasticity. The J-integral values under the fully plastic condition are estimated for four semi-elliptical or semi-circular surface cracks in plates subiected to bending loads. Some discussions are made concerning the J-integral distributiom along the crack front. The maximun J -integral value is found near the free surface for deep cracks. Also the numerical solutions are applied to the simplified estimation of the growing crack geometry. The crack growth in the width direction is dominant for deeper cracks. As a result, penetration through the plate-thickness does not occur in all cases analyzed.

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In order to study the origin of the scatter in the fracture toughness values by small specimens in the transition region, the J-integral measurement in the fracture toughness transition region was performed using more than 100 small specimens of Ni-Cr-Mo-V steel, and fractured surfaces were studied very carefully, aiming to obtain better understanding of the scatter in the small-specimen toughness. The study discloses that a major portion of the scatter was caused by the scatter in the length of the preceding dimple crack, which was generated at the fatigue precrack before the initiation of the final cleavage fracture. A method to predict the lower bound of the scatter in the small-specimen fracture toughness was also proposed.

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The thermoelastoplastic stresses caused within a large-scaled low-alloy steel shaft material, which has a circumferential groove in the longitudinal center of its axis, are dynamically simulated by FEM based on the incremental strain theory under the two different cooling conditions, i. e. water and air. An inner tensile peak stress zone and compression stress concentration areas along the groove move through the cooling process because both the plastic deformation at the surface and the non-similarity of volumetic expansion due to transformation are compounded. As a result, characterizing the residual distributions on principal stresses, σ₁ and σ₂ are close with the inner in the air cooled zone compared with the water cooled, and σ₃ shows high compression stress concentrations at the fillets of the groove.

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Plastic behavior of S25C Mild Steel was investigated at constant temperatures and variable temperatures in the range from room temperature to 400'C. Combined loading tests were carried out by applying axial loads and pure torsion to thin walled tubular specimens. The initial yield condition followed the Tresca law, but the stress-strain relation loading conditions were different from those by the axial loading conditions. The stress-strain relations at certain temperatures subsequent to the tensile pre-strain subjected at another temperature were obtained. The experimental results were compared with the stress-strain relation at a constant temperature.

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The finite element formulation of the coupled analysis of plastic deformation and heat conduction is studied for the numerical analysis during the metal forming process at elevated temperatures. As an extension of previous studies, a method of estimating equivalent plastic strain during the steady-state forming process is proposed in the present study, which is applicable to both strain and strain-rate dependent materials. As an example of numerical calculation, the coupled heat and deformation analysis for an axisymmetric steady state dieless drawing is performed. The distribution of temperature, plastic strain rate, equivalent plastic strain and the change of billet shape during dieless drawing are calculated. The obtained results are in good agreement with experimental data. The influence of the work-hardening exponent on deformation and the distribution of temperature is also discussed.

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A constitutive equation taking into account the effect of the void volume fraction on the macroscopic elasticity moduli has been developed. An additional strain rate is derived from the partial differentiation of the elastic stress-strain relation with respect to the void volume fraction and is added to the strain rate obtained from the original Gurson type constitutive equation. The deformation behavior of a plane strain block with both ends fixed subjected to tension has been analyzed. The comparison between the results obtained by employing the present constitutive equation and the original one clarified that the void volume fraction dependency of macroscopic elasticity moduli has a substantial effect on the residual stress, but not on global deformation behavior.

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A new approach to describe the cyclic plastic deformation of a carbon steel was presented by applying and extending the cyclic plasticity model proposed by the authors in the previous paper, based on the random barriers theory. The field of resisting force against the movement of dislocations regulating the stress-strain curve in each half cycle could be expressed by using the density function given by a composite Weibull distribution having a parameter of division which was named in this paper as the border stress. As a result of discussions with some experiments, it was clarified that the cyclic hardening or softening behavior of a carbon steel under constant strain cycling tests, both in the initial stage and in the case after the strain range increases or decreases in the steady stage could be described by a unique rule based on the change characteristics of the force field depending on the stress and strain history.

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The rigid plastic finite element method is frequently used to predict the deformation behaviour of the materials during the forming processes. The constitutive equation employed is usually restricted to flow type one so that the normality of the strain rate to the yield surface is entailed. Then the deformation can not follow the abrupt change in stress history. This often yields the over stabilization of the deformation. In this paper, to overcome this situation, a rate type constitutive equation with a one-to-one relation between stress rate and strain rate is employed, and the formulation of the rigid plastic finite element method is presented. The method is applied to the prediction of the flow localization of the strip under tension. The feature of the present results is clarified by comparing the results with those due to J2 flow and corner theory.

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The stress and displacement fields at the close vicinity of a bonding edge show singularity behaviors. So, the adhesive strength evaluation method using maximum stresses, which were calculated by numerical stress analysis such as the finite element method, is generally not valid. In this paper, a new method, which uses two stress singularity parameters, is presented for evaluating adhesive strength. This method is applied to several kinds of molded models, composed of epoxy base resin and Fe-Ni alloy sheets. Predictions about the initiation and extension of delamination are compared with the results of observations made by ultrasonic tests on molded models.

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This work is a preliminary investigation carried out in an attempt to develop a software system which detects the possible sources of degradation in the original design of machines and structures and provides alternatives to improve their integrities in terms of strength by noting their geometrical distinctions. The computer stores their topological data using a boundary representation model. The system detects the distinctive geometrical features and reasons based on them whether they might be triggers for degradation or not by referring to the attributes attached to each one of these geometrical features. The fundamental validity of the approach is verified on a personal computer using Prolog. What should be stressed as the originality of this paper is that although the design models cannot be modified without numerical data in the conventional strength-related designs, they can be improved, or better alternatives can be suggested, as long as their topological data are available in our system.

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