High-cycle rotary bending fatigue tests were conducted on a supercarburized low-alloy steel. Special attention was paid on how the eutectoid carbide contained in the material affects the fatigue process. The metallographic and fractographic observations of the fatigue process, revealed that although debonding at the matrix/carbide interface occurs at the initial stage of the fatigue process, final failure was induced by the growth of a crack initiated at the weak site of retained austenite grains. At the fatigue limit, the growth of the weak-site-initiated crack was blocked by the surrounding carbide particles.

抄録全体を表示

In a fundamental study on austempered ductile iron, rotating bending fatigue tests were conducted with respect to environment durability. The S-N curve in this environment showed a tendency toward low fatigue limit. Fatigue fracture in high cycles was verified by changing the viscosity of grease. However, the typical fish-eye in the long-life region ( >10⁷ cycles) was not observed on the fracture surface. When a low viscosity of grease penetrates into the cracks, crack propagation accelerates due to the wedge effect. The surface is brittle locally, because martensite in the matrix structure is formed by the work hardening process mentioned above. It is suggested that fatigue strength will be lower with the use of oils, because cracks initiate easily from martensite parts.

抄録全体を表示

Link chains used in chain hoists are often subjected to combined loads of torsion, tension, dynamic and bending moments. They are usually fractured by fatigue. A few investigations have been carried out on the behavior of fatigue for link chains. In this paper, a procedure for a prediction S-N curves is examined using three dimensional elastic-plastic finite-element analysis and Coffin-Man-son's law. Fatigue tests were conducted for link chains in order to examine fatigue strength of 10⁶ cycles. It is found that the procedure suggested in this paper is quite stuitable for the prediction of S-N curves. From the fatigue tests and the finiteelement analysis, it is found that a crack initiates from the border between the straight part and the curved part of the inner surface of a link chain. Comparison between the numerical and the experimental results is made for the strain measurement and stress distribution. The numerical results corresponds with the experimental results fairly well.

抄録全体を表示

In order to clarify the strength characteristics of alumina joints, static strength and cyclic fatigue tests were carried out for joints of Al₂O₃/Al₂O₃ and Al₂O₃/Mo/SUS304/Mo/Al₂O₃ formed with Ticusil and Cu₈₀Ti₂₀ fillers in vacuum. Static tests were conducted at room temperature and elevated temperature. Fatigue tests were conducted at constant stress ratio R (=0.1) and constant frequency f (=50 Hz) at room temperature. The strength characteristics of the joints of Al₂O₃/Al₂O₃ formed using Ticusil were basically the same as the strength characteristics of Al₂O₃. The strength characteristics of the joints of Al₂O₃/Mo/SUS304/Mo/Al₂O₃ were mainly determined by the strength characteristics of the joint of Mo/Al₂O₃.

抄録全体を表示

The effect of carbon content on fatigue crack initiation behavior has been investigated by the plastic replica method using four kinds of carbon steels with the same size of ferritic grains. The fatigue limit of each of these materials has been related to the existing limit of the nonpropagating cracks. Therefore, the purpose of this study is mainly to examine the effect of carbon content on the existence of nonpropagating cracks. From the experimental results, it appears that the nonpropagating cracks in low-carbon steels (S 15 C and S 25 C) were almost blocked by the boundaries of ferritic grains. On the other hand, nonpropagating cracks in medium-carbon steels (S 35 C and S 45 C) tended to be blocked by pearlite. Though it is well known that fatigue limit is proportional to the mean grain size according to the Hall-Petch equation, that of these materials of the same ferritic grain size was strongly dependent on carbon content.

抄録全体を表示

The influences of carbon fiber (CF) on fatigue crack propagation (FCP) of advanced Nylon 46 (N46) were studied in comparison with glass fiber (gf)-reinforced N46. FCP properties were estimated vertical to the injection direction of the molding plate. Three kinds of specimens were tested : 30 wt %gf-, 15 wt %CF- and 30 wt %CF-reinforced N46 (described as gf30, CF15 and CF30, respectively). The values ofΔK at da/dN=10^-9 m/cycle, ΔK(10^-9), were 2.8, 2.8 and 3.2 MPa √(m), respectively. From fractography using SEM, it was shown that the effect of reinforced fibers on FCP was manifested as fiber bridging. Furthermore, from thermographic nondestructive testing using infrared thermography, it was found that the variation in FCP of each specimen was related to the crack tip opening displacement.

抄録全体を表示

A previous study reported that the existence of molten salt on the surface of cracked silicon nitride sintered under no pressure enhanced the strength significantly at 900°C where the specimens were exposed to a burner rig. This study investigated the strengthening mechanism of cracked silicon nitride in the presence of molten salt using another kind of silicon nitride that is sintered under high pressure. In these experiments the tensile tests were carried out at 1000°C using low-quality fueled burner rig and bending tests were also carried out at 900, 1000 and 1200°C on an electric furnace to the sodium sulfate applied specimens. Surface flaw was induced on these specimens by Vickers indentation, a blast abrasive or a glass cutter. In low-quality fueled combustion gas, the tensile strength of cracked specimens is comparable to that of the non-cracked or smooth specimens and the data obtained show no scatter. In contrast, in the electric furnace test, the bending strength of cracked specimens to which sodium sulfate was applied showed considerable scattering under the corrosive environment contained a sodium and a sulpher. This difference is dependent on whether the molten salt enters the cracks or not. Some experimental findings to support this hypothesis are obtained with EPMA.

抄録全体を表示

A method of interferometry is applied to study the near-tip field of cracks which are propagating in PMMA specimens at a speed of about 550 m/s. The interference fringes around the cracks are photographed with a holographic optical system at 18 μs or at 73 μs after the crack initiation. The interference fringes are measured and analyzed in the directions of ±72 degrees from the propagation direction of the crack in order to compare the measurement results obtained through interferometry with those through the caustic method. It is found that the effect of higher order terms appears in the near-tip field at 18 μs after the crack initiation, but disappears at 73 μs, and the singular field is developed as far as 9 mm from the tip. Consequently, it can be concluded that, in the directions of ±72 degrees from the propagation direction, the effect of higher order terms appears within several tens of microseconds after the beginning of rapid crack propagation where crack speed is more than it few hundred m/s. These results are in good agreement with those obtained through the caustic method.

抄録全体を表示

A series of creep-fatigue tests was conducted with Modified 9Cr-1Mo steel at 600°C in 0. 1 mPa vacuum to assess the accumulation of creep-fatigue damage. In these tests, each test specimen was subjected to prior creep-fatigue loading followed by subsequent fatigue loading or prior fatigue loading followed by subsequent creep-fatigue loading. The linear summation of cumulative damage of fatigue and creep life fraction was smaller than unity for the former case, and larger than unity for the latter case. The damage model based on the overstress concept was applied to the test results to verify its applicability. The accuracy of the life evaluation was not enough because of the nonlinear interaction between creep and fatigue.

抄録全体を表示

Thermal buckling analysis of moderately thick symmetric and antisymmetric laminates having simple supports and subjected to a uniform temperature rise and linearly gradient temperature variation through their thickness (linear temperature variation) is investigated in this study. Transverse shear deformation is taken into consideration by employing the first-order shear deformation theory (Reissner-Mindlin theory), and closed-form solutions of the critical buckling temperature are obtained. Numerical results show the effects of various factors such as temperature fields, stacking sequence, number of layers and plate aspect ratio on the critical buckling temperature. Moreover, the thermal buckling characteristics are clarified for the heat quantity and thermal force variation, which has an influence on the critical buckling temperature and buckled mode shapes for each temperature field.

抄録全体を表示

Damage growth in carbon/epoxy composite laminates was studied using an instrumented falling weight impact machine. Two kinds of quasi-isotropic (45°/0°/-45°/90°)_2s laminates were used in order to investigate the effects of resin toughness and fiber strength. After impact at various energy levels, the thermal deply technique was applied to investigate the three-dimensional distribution of damage such as fiber breakage and delamination. In each kind of laminate, the absorbed impact energy was found to be a linear function of both the main crack area with fiber breakage and the total delamination area. Thus, the absorbed energies per unit area due to fiber breakage, and due to delamination could be determined independently. The differences between two kinds of laminates suggested that the increase in interlaminar fracture toughness increases the energy absorbing capability due to delamination, while it decreases the capability due to fiber breakage.

抄録全体を表示

Compressive prestresses were applied to isotropic fine-grained graphite at room temperature (RT) and high temperature (2010°C). As a result, decrease in Young's modulus due to high-temperature prestressing was 56% which was much larger than the 6.4% that was due to RT prestressing. This finding was considered to be due primarily to difference in degree of preferred orientation of crystallites in the graphite on the basis of Bacon anisotropy factor (BAF) from X-ray diffraction measurement of the prestressed specimens. Furthermore, high-temperature compressive prestressing produced an increase in the strength of the isotropic graphite, although room temperature prestressing produced no such effect. The results obtained here suggest that isotropic graphite which is subjected to high-temperature compressive stress becomes anisotropic.

抄録全体を表示

Stress corrosion cracking (SCC) of pure copper has been under investigation for over 30 years. Various researchers have reported that Cu fails via a tarnish-rupture mechanism. Recently, the strain rate sensitivity of SCC on Cu alloys was studied using the slow strain-rate test (SSRT). This method may not be adequate to verify the validity of the tarnish-rupture mechanism because of the slow strain rates employed. In the present study, the crack initiation and growth mechanisms operating during SCC of pure Cu were studied. The specimens used were manufactured from 99.9wt. % vacuum-annealed Cu. The corrosive medium was 3.0 kmol. m^-3 NaNO₂ solution at 293±3 K. A range of dipping times (t_P), holding times (t_H), and total strain (ε_T) were utilized. In this context, t_P is the time for which the specimen was dipped in the solution prior to the start of the strain application, t_H is the time for which the specimen is held while being subjected to a fixed amount of strain E and ε_T is the total strain applied to the specimen during step-strain testing (SST). The results can be summarized as follows. Three different modes could be identified through SST. These modes were classified as A, B and C in this study. In type A, no cracking occurred in the Cu even though a film formed on the Cu surface. In type B, the crack formed but did not propagate through the depth. In type C, the crack propagated through the specimen thickness and then grew along grain boundaries. It was also found that SST was capable of generating more severe conditions than SSRT. This is illustrated by comparing the stress-strain curves to failure for SSRT and SST.

抄録全体を表示

The homogenization method is applied to the analysis of a composite material whose constituents reveal elastoplastic character as well as finite deformation. Since the updating Lagrangian scheme with rate forms guarantees the instantaneous linearity of the governing equations, it is possible to use the separation of variables in the two-scale asymptotic expansion of the solution. Furthermore, the updating scheme also enables us to utilize the microscopic stress field, which is obtained in a localization process, in the judgement of plastic failure. A review of the general procedure for the asymptotic homogenization method supports our present discussion. Although the large deformation and small strain are assumed as the mechanical responses of both macro and microscopic structures of a composite, the periodicity assumption is not violated in a local region. Thus the total deformation of the composite can be obtained as accumulation of a series of "instantaneous" solutions.

抄録全体を表示

Behavior of hardening parameters for viscoplastic constitutive equations was discussed on the basis of the experimental results of type 316 stainless steel for a wide range of temperatures from room temperature to 7000°C. It was elucidated first that the cyclic hardening under proportional loading can be described by the expansion of the range of kinematic hardening variables at each temperature. This behavior is especially significant around 500°C. For cyclic hardening under non proportional loading, on the other hand, marked development of isotropic hardening was observed. Then, new evolution equations of kinematic hardening were proposed by incorporating these results. The applicability of the resulting constitutive models was demonstrated by comparing the predictions with the corresponding result of the experiments.

抄録全体を表示

Applicability of the elaborated constitutive equations of cyclic plasticity proposed by the present authors is discussed in detail. New evolution equations of non linear kinematic hardening of the viscoplastic constitutive models developed in the previous paper with special emphasis on the characteristic expansion of the kinematic hardening range observed in the cyclic hardening of type 316 stainless steel at 400°C to 500°C were employed. The predictions of the proposed constitutive equations were compared with the corresponding experimental results of cyclic plasticity for various temperatures and loading conditions. The proposed constitutive equations were found to describe accurately the proportional and non proportional cyclic behavior, in particular the effects of strain amplitude histories, for a wide range of temperatures from room temperature to 700°C.

抄録全体を表示

It is well known that ultrasonic wave velocity is changed by elastic deformation (stress) and also by microstructural material property change, i.e. the rotation of crystals (so-called texture) due to plastic deformation ; this phenomenon is called acoustoelasticity or acoustoplasticity. The relation-ship between texture and ultrasonic wave velocities has been derived by Sayers using the crystallite orientation distribution function (CODF). In the present study, the Sayers's model is examined by comparison of the simulation results due to the CODF with the experimental data of the longitudinal and transverse wave velocities in both annealed and non-annealed aluminum alloy. Moreover, we study the rotation of crystals, i.e. texture, due to plastic deformation using the pole figure calculated by the CODF.

抄録全体を表示

To date, in the sheet forming process design the data base decision system based on experience and experimental observation has been commonly employed. This paper propose for the first time an optimum process design system based on two numerical simulation schemes. One is forming simulation using the finite element method. The other is mathematical programing, such as the grid search and simplex methods. In this system, the objective function is formulated by design parameters, such as tool size, process stage, and material properties. Optimum search is performed under a constraint condition by employing the nonlinear programing and finite element methods. This system is applied to the two-stage press forming of a thermoplastic plate to achieve uniform thickness of the products. It was confirmed by comparison with experimental observations that the hybrid method which combines the grid search method and simplex method can determine the optimum condition accurately and efficiently.

抄録全体を表示

Stress wave propagation and dynamic stress concentration in single lap adhesive joints under dynamic loading were investigated analytically and experimentally. Stress distribution and time variation of stress in joints under tensile impact loading were calculated considering viscoelastic properties of adhesive using the F.E.M.. Impact examimation for an adhesive joint of aluminium alloy was conducted. High stress concentration was generated at the end of the joint. Increasing lap length is not effective in reducing initial stress concentration in the joints. Effect of adhesive thickness on the concentration of stress was examined using calculated results.

抄録全体を表示

In this paper we present a simple equation for estimating plastic deflection of steel panels subjected to impulsive loading. This equation describes the relation between the plastic deflection and the impulsive load through a linear approximation based on the least squares method. In order to prove the equation's validity, the authors conducted an experiment on a panel subjected to impulsive loading caused by an underwater explosion. The resulting plastic deflection in this experiment and that determined from the estimation equation were compared, and the validity of the equation for estimating plastic deflection with sufficient accuracy was confirmed.

抄録全体を表示

The compressive strength of an intermetallic compound γ-TiAl, was characterized at temperatures from 77 K to 1073 K and at strain rates from 10^-4 s^-1 to 103 s^-1. At low temperatures, flow stress increased with decrease of temperature and with increase of strain rate, and an abnormal increase of stress was observed, probably due to the dynamic interaction of dislocations with lattice defects at relatively high temperatures where negative strain rate dependence of stress was also observed. The higher the strain rate, the more the interaction becomes marked at higher temperatures ; consequently, a minimum strength at intermediate temperatures can be expected. The concept of a thermally activated process gives a plausible explanation of the experimental results in the given temperature ranges, and allows prediction of the dynamic behaviors of this kind of material.

抄録全体を表示

Powder packing behavior is analyzed by the method based on the equilibrium equation of contact forces between particles. Contact forces employed in the calculation are repulsive force and friction force. Repulsive force is estimated by the rigid-plastic FEM. Three dimensional calculations for various strain ratios are carried out by 6-particle modeling and 800-particle modeling. Mean normal stress and octahedral shear stress are employed to show the relationship between stress and density ratio. The calculated result agrees qualitatively with that of the experiment. However calculated stresses are approximately 1/6 of those in the experiment.

抄録全体を表示

FEM simulation of the strain localization in sheet metals is performed using crystal plasticity theory. The constitutive relations formulated by Asaro et al. are used, in which the rate-dependent property is included so as to determine active slip systems uniquely for a strain increment. The strain localization which appears in a silicon iron sheet under uniaxial tension is calculated. All 48 slip systems of the bcc crystal are considered, and isotropic hardening for the relationship between resolved shear stress and strain is assumed. Strain localization is affected by the combination of the activated slip systems. The analytical results are compared with those of experiments. The dependence of localized deformation mode on initial lattice orientation is predicted well by numerical results.

抄録全体を表示

Shape of graphite particles in cast iron varies widely depending on the casting and heat treatment conditions. Mechanical properties of cast iron are strongly affected by the matrix microstructure and geometrical characteristics of the graphite particles such as size and shape. In this study, quantitative analysis of the sectional shape irregularity of such graphite particles within cast iron was carried out by applying a fractal concept. Fractal dimension thus obtained was not sufficient to represent macroscopic shape irregularity, although microscopic irregularity was success-fully evaluated. In order to evaluate macroscopic irregularity, the "Macroscopic Shape Index" was proposed here by combining Kaye's procedure with the Fast-Fourier-Transformation technique. This index was found to be useful in quantitative evaluation of the macroscopic irregularity.

抄録全体を表示

The tensile deformation and damage behavior of 2024-T6 aluminum alloy reinforced by 2% and 10% SiC particles are studied. SEM (Scanning Electron Microscope) observation shows that the fracture occurs due to the dimple fracture of matrix, interfacial debonding of particle and matrix and particle cracking. These fracture processes are simulated numerically using Gurson's constitutive equation with large-deformation theory. It is shown that the nonuniform distributions of particles have a large effect on the microfracture process, and the effect of the initial debonding and particle cracking are discussed.

抄録全体を表示

Notch tensile strength of circumferentially notched cylindrical bars with ring protuberances on both notch shoulders is investigated. The protuberances are employed to increase stress triaxiality near the net section. The notch tensile strength increases with increasing diameter and length of the protuberances. The protuberances quenched only in the thin layer from those surfaces produce higher notch tensile strength than the unquenched protuberances. The stress triaxiality factor obtained from FEM calculation is proportional to NSR or the ratio of notch tensile strength to unnotch tensile strength. FEM simulation shows that when both notch shoulders are quenched ideally to higher yield stress, NSR of a shallow notch is nearly equal to NSR of a deep notch ; NSR of a deep notch is much higher than NSR of a shallow notch unless the quench is performed. This indicates that notch shoulders are one of the most important factors determining notch tensile strength.

抄録全体を表示

This paper describes a study on X-ray stress analysis using a two-dimensional X-ray detector. An imaging plate (IP) was adopted in this study as one of the two-dimensional detectors, which enabled us to obtain whole diffraction patterns rapidly and accurately and also to analyze their digital data in a computer. A new X-ray triaxial stress analysis, which is fitted to use the two-dimensional detector, was presented. This method was applied to measure residual stresses, introduced by grinding, as well as applied ones on a steel. The stresses measured by the present method agreed well with those measured by the conventional Dolle-Hauk method. The scattering of stresses obtained by the present method was almost the same as that obtained by the conventional method. The time of measurement for full triaxial stress analysis by the present method was almost one-thirtieth that of the conventional one. It was found that the use of IP effectively shortened the measurement time in case of triaxial stress analysis, compared with the case of plane stress analysis.

抄録全体を表示

This paper is concerned with the dynamic treatment of thermal stresses in an infinite plate of functionally graded material (FGM) subjected to uniform impulsive electromagnetic radiation. Heating is assumed to be a step function in time, and to diminish exponentially with the distance from the exposed surface of the plate, assuming negligible heat conduction. In treating problems, the nature of the stress-wave buildup in the absorption plate is studied for the case of a temperature-dependent solid, i.e., when material properties vary with temperature. The numerical procedure employs the characteristic method based on the integration of the governing equations along the characteristics. Numerical examples are presented for several PSZ (partially stabilized zirconia)/SUS₃₀₄ (type 304 stainless steel) FGM showing the significance of the dynamic effects and the temperature-dependent properties of material to the thermoelastic material design of FGM.

抄録全体を表示

To introduce the numerical simulation technique for the design sites of industrial products, a "CAD/CAE seamless" system from modeling to computation is desired. A gridless or element-free method is expected to be an effective procedure for realizing such system, because time-consuming mesh generation processes can be omitted. The Element-free Galerkin method (EFGM) proposed by Belytschko et al⁽⁶⁾. is one of the practical gridless methods. This study describes an application of EFGM to solve boundary problems of a one-dimensional ordinary differential equation. A new methodology of enforcing the essential boundary condition in the EFGM formulation is proposed, and the accuracy of the present method is verified.

抄録全体を表示

Since weld-bonded and bonded structures exhibit higher performances than spot-welded structures, they can be used to reduce the weight of car body structures. In this paper, a dissipated strain energy method is applied to predict loss factors and natural frequencies of weld-bonded and bonded box section members. For comparison with numerical results, an experimental study for measuring the loss factor and the natural frequency of double-hat-type box section members was carried out using an impulse-frequency response technique. Good agreement obtained between the numerical and the experimental results indicates that the analytical methods developed here are satisfactory for predicting the loss factor and the natural frequency. Furthermore, the change in the loss factor and the natural frequency with spot welding pitch and thickness of the adhesive layer is examined. It is found that the loss factor of the weldbonded box section members does not depend on spot welding pitch and is higher than those of the spotwelded box section members.

抄録全体を表示

Polymers show viscoelastic response, in which the ultrasonic phase velocity depends on the frequency. From the linear response theory, we obtain the general expressions which relate the phase velocity dispersion to the frequency dependence of the attenuation coefficient. Assuming that both changes in the phase velocity and the attenuation with frequency are small, O'Donnell derived a practical expression based on the Kramers-Kronig relation. In this study, we measure the phase velocity and the attenuation of longitudinal waves from 4 MHz to 12 MHz for PMMA (polymethyl methacrylate), polyethylene, and 6-nylon specimens using a superheterodyne phase-sensitive system. The results show good agreement with the prediction from O'Donnell's expression.

抄録全体を表示

A nanoindentation hardness apparatus was developed on the basis of an atomic force microscope to obtain both an indentation curve and an indentation image. Newly devised features were to use a lever which has a three-sided pyramidal diamond tip at the central part of the lever, to measure the vertical displacement at the center of the lever and to add an actuator for controlling the force. The ultra-microhardness values of gold, SUS403 steel and SNCM439 steel measured at the indentation forces between 2.6×10³ and 3.5×10³ μN using the nanoindentation hardness apparatus agreed with the macrohardness values measured at the force of 4.9 or 9.8 N using the conventional Vickers hardness apparatus. However, the ultra-microhardness increased with decreasing indentation force. This behavior was explained considering the elastic-plastic conditions of the specimens.

抄録全体を表示