Plane bending and cyclic torsion tests, and a combination of them are first carried out with a stress ratio R=0 using annealed cracked specimens made of carbon steel. The threshold stress of micro fatigue crack propagation under a mixed mode can be well determined using the maximum principal stress criterion because of no crack closure in this case. Next, plane bending tests are performed with various stress ratios R. Based on the assumption that crack opening displacement on the threshold level is constant regardless of R, the relation between R and the threshold stress is formulated. The suggested expression is found to be in good agreement with the test results and can be applied to the whole range of the stress ratio.

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Experimental results are presented for time-dependent crack growth obtained from load-hold testing at room temperature. The test are carried out over a wide range of loading rates before load holding, which includes a high rate as well as a low rate. First, it is shown that when the load is applied with a high rate, the threshold value of load holding for ductile instability is not limited to values near the maximum load as reported so far, but decreases. Next, the condition is clarified for the transition of time-dependent crack growth from stable to unstable. Then the incipient point of the transition is studied, where the incipient point is defined as a point from which the rate of the crack-mouth opening displacement increases. It is found that the incipient point occurs when the macroscopic deformation of the specimen under a constant loading attains that at the maximum load under monotonic loading.

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In order to examine the threshold condition for the propagation of a through crack under the mixed mode, plane bending and cyclic torsion tests, and various combinations of them are carried out under the condition of the stress ratio R=-1 by using annealed center cracked specimens made of carbon steel. Taking account of the frictional stress acting on the crack surface under cyclic torsion, and adopting the strain energy density criterion, the threshold stress of crack propagation under the combination of plane bending and cyclic torsion can be deduced from the test results of plane bending and cyclic torsion.

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In the general area of fatigue crack growth in the presence of residual stresses, it is noted that the correction of stress intensity factor (K) to account for residual stresses is important for the determination of both the range and ratio (R) of K during a loading cycle. The superposition technique can be applied generally for the determination of K. For compact specimens, however, a redistribution of residual stresses occurs during crack growth and its effect is noticeable. In this study, experiments and analyses were done for compact specimens which had two orientations such that the crack grew through the weld metal of a butt weld joint of carbon steel parallel to or perpendicular to the weld line. The results obtained are as follows : (1) For the compact specimen, it is possible to predict the crack growth rates by using the superposition technique. (2) When the crack grows first through the compressive portion of a residual stress field, the effect is actually a result of the ratio (R) of K.

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A stress-strain response of 21/4 Cr-1 Mo steel at 550°C was investigated, based on the creep-fatigue test results obtained by the authors, as shown in the previous report The following observations were made. The stress-strain response of this material is not affected by a test environment but by loading conditions. Internal stresses were determined from an analysis of unloading curves. The internal stress consists of a back stress and a drag stress. A drag stress corresponds to the radius of an elastic core. The overstress was also determined phenomenologically. The value of the overstress of this material does not depend either on the inelastic strain rate or the strain range thus far as investigated. Back stress softens as the material softens, but the overstress and drag stress are almost constant until failue. The above observations are compared with those for 304 steel.

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Rotating bending fatigue tests were carried out on plain specimens and specimens with a small blind hole of an age-hardened Al-alloy and an annealed Al-alloy in air and in oil. The main results obtained are as follows : l) Fatigue crack growth rate in the annealed Al-alloy is suppressed, and that in the age-haredned Al-alloy is accelerated due to the existence of oil, although the fatigue crack initiation process is hardly affected by oil in both Al-alloys. 2) Fatigue crack growth rate of the age-hardened Al-alloy is inceased with an increase in the viscosity of the oil. 3) There is little influence of oil on the crack topography or the fracture mechanism in both Al-alloys.

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Slow strain rate tests (SSRT) have been carried out using precracked compact tension specimens of low alloy steels in purified hydrogen gas at ambient temperature. By the use of elastic-plastic fracture mechanics parameters, the influence of hydrogen gas on sub-critical crack growth has been investigated in terms of the J-value at the onset of crack extension and also from a view point of fracture modes. Acoustic-Emission (AE) during the SSRT tests has been monitored to clarify the cracking behavior in hydrogen gas and by mechanical tearing. In a hydrogen gas environment, it is clearly shown that a crack initiates and propagates in a quasi-cleavage manner until applied the J value reaches J₁c and after that the fracture mode changes to mixture of ductile dimple and quasi-cleavage. This result suggests that mechanical tearing occurs at J-values greater than J₁c even in a hydrogen environment. In SA 533 B steels, the AE activity showed two energy peaks with respect to loading levels, whose origins are attributable to the onset of quasi-cleavage fracturing caused by the environment and to the onset of mechanical tearing.

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This paper is concerned with the problem of fast crack propagation and arrest. The crack tip position versus time is measured by the ladder gages for the double-cantilever beam specimens machined from the model material, polymethylmethacrylate. Using this data, the dynamic stress intensity factor of the running crack is calculated by an improved finite difference method. In this FDM, the stress at a node adjacent to the crack tip is gradually relaxed depending on the crack tip location between nodes. The solutions of the equations of motion obtained by the central difference approximation are corrected by the trapezoidal rule. With these techniques, the crack propagation processes are simulated more accurately by an explicit time-step algorithm with little computing time required.

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Ductile fracture of surface crack is studied experimentally and numerically. At first, fatigue pre-crack is introduced, and the aspect ratios of the growing fatigue crack are measured. Then the ductile fracture test is carried out and the distributions of SZW and Δa are measured. It is noted that Δa is largest where φ, the angle from surface, is nearly 30°C. J integral distribution is evaluated by the finite element method, and it is shown that the J value is also the largest where φ is nearly 30°C. J integral distribution is evaluated by the finite element method, and it is shown that the J value is also the largest where φ is nearly 30°C.

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In this paper, it is experimentally proved that the onset of tearing instability is evaluated simply through the equilibrium of stiffeness between the external structure and the crack member ; that is, the slope of the load versus the load line displacement (P-V_g) curve. A procedure to estimate the instability from the P-V_g characteritics of compact tension specimens with a wide range of crack length to width ratios loded in series with a spring is proposed, and it agreed well with the experiments for two materials. An approximate procedure to apply the concept to actual structures without using a fracture mechanics parameter such as J or T is discussed. An example of the practical application is shown, in determining expressions for the instability conditions of a circumferential or axial crack in a cylindrical vessel or pipe.

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This paper deals with the electromagnetoelastic problem of a circumferential edge crack in a cylindrical cavity under a uniform axial electric current flow and a constant axial magnetic field. The current flow is disturbed by the presence of the edge crack and the torsional stresses are caused by the interactions between the magnetic field and the disturbed current. Two problems concerning the electric current density field and the electromagnetoelastic field are formulated by means of integral transforms and reduced to two singular integral equations of the first kind. Numerical calculations are carried out and stress intensity factors are obtained for several values of geometric parameters.

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In this study, stress concentration factors and fatigue strength reduction factors are obtained in the case of a round bar of mild steel with a V-groove under ultrasonically vibrating stress. The stress concentration factors are determined by analysis on eigenmodes using FEM. The fatigue strength reduction factors are also obtained by combining the analysis and the results of the ultrasonic fatigue tests. The factors under ultrasonically vibrating stress are firstly determined. Based on these results the ultrasonic fatigue test may become more popular as an ordinary fatigue test.

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This paper deals with the stress concentration problem of a circular solid cylinder with a central notch and two supplemental notches under tension. Stress mitigations due to the interference effects of stress concentration are investigated. We consider the influences of the distances between a central notch and two supplemental notches and the radii of the semicircular notches on the mitigations of stress concentration. The principle of the method of solution makes use of distributing body forces in the interior of a solid cylinder in order to satisfy the boundary conditions of the notched surfaces, which are imagined in the solid cylinder with no notch. For this purpose, we apply Green's functions for body force problems of an infinite solid cylinder. Numerical results are shown for stress concentration factors of the problem.

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The conventional rate type constitutive equations of elasticity are critically examined. By introducing finite strains in the dual coordinate system for Green-Lagrange, Almansi-Euler and Storen-Rice strain tensors, the relations among these strains and their rates are clarified. From the viewpoint of rational mechanics, the admissible forms of the general constitutive equations are obtained, and their rate forms are compared with the conventional rate equations. It is concluded that Green-Naghdi stress rate should be used in the rate type constitutive equation, while Jaumann stress rate should be used in the Updated Lagrangian formulations.

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The longitudinal impact of a slightly curved bar by a rigid hammer is analyzed numerically, and the residual deformation of the bar is investigated. The dynamic elasto-plastic deformation behavior, for the time after reimpacts as well as the first impact, is discussed for a bar subjected to a plastic strain of the same order as the elastic. The governing partial differential equations are approximated by means of finite-difference equations. The residual deformation of the bar was evaluated by the residual axial displacement of the struck end. As a result, it was shown that the residual axial displacement was expressed by the product of the power function of the mass ratio of the rigid hammer to the bar and that of the impact velocity. The experimental results on aluminum bars were in good agreement with the numerical results.

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In this paper, the finite element method to analyze the thermal stresses of an adhesive bonded structure, of which the adherends are two-dimensional elastic bodies with optional shapes, is proposed. In the analytical model, the adhesive layer is assumed as the heat conductive pipe for the thermal condition and as the spring element transmitting only a shearing force for the dynamical load condition. These stiffness matrices are formulated to match the well-known finite element method for in-plane analysis of the plate. By using this method, the stress distributions of adhesive bonded structures, of which the adherends are composed of copper and acrylic resin plates, under uniform and nonuniform temperature fields are analyzed. From the results, it is established that the shearing stress at the adhesive layer reaches very large values at the boundaries between the two plates.

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To continue the work presented in the previous paper, the solution to the problem of the interaction between two circular inclusions and an edge dislocation in an infinite plate, which are arranged in the order of inclusion-edge dislocation-inclusion, and are placed on the x-axis, having the glide plane inclined to the x-axis. Results obtained by numerical calculation indicate that, for the region near the interface, the interactions are affected by the combinations of elastic constants and the inclination of the glide plane. The dislocation has a stable equilibrium position or an unstable equilibrium position at some intermediate distance from the inclusions under some combinations of elastic constants. The equilibrium positions are also affected by the inclination of the glide plane.

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The propagation of the Luders' bands in straight specimens of mild steel of various cross-sectional shapes under uniaxial tension is investigated by use of the Moire-fringe method. It is confirmed that a discontinuous deformation takes place acorss the Luders' band. A numerical simulation of the propagation of the Luders' band (elastic-plastic boundary) in the notched sheet specimens of a rimmed steel is performed by incremental elastic-plastic FEM with a new idea about the yield-point-elongation phenomenon and is confirmed to agree well with a corresponding experiment which is visualized by the Moire-fringe method with a new technique. The idea is that the typical yield-point elongation strain in the stress-strain curve of an arbitrary infinitesimal element in a mild steel should be understood as the strain which jumps drastically, and not as a continuous property as conventionally understood.

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The stress-strain-optic relations of cellulose acetate are much influenced by strain-rate or room temperature. This fact has caused great difficulties in the stress analysis with photoplasticity. In this paper, to obtain the fundamental relations for photoplastic stress analysis using cellulose acetate not only the effect of strain-rate but that of room temperature on the mechanical and the optical properties were investigated precisely by means of the uniaxial tension test. As a result the yield stress, Young's modulus and the yield fringe order were expressed by a linear function of the logarithmic strain-rate and temperature. Moreover, the stress-strain, the stress-fringe order and the fringe order-strain relation were uniquely represented in nondimensional forms regardless of both strain-rate and temperature. Finally, it could be confirmed that the strain-rate was obtained from measurements of both fringe order and fringe order-rate. Therefore, it is possible to estimate the distribution of strain-rate as well as stress or strain in the photoplastic model.

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In the previous paper, the authors reported the empirical formulas for photoplastic stress analysis using cellulose acetate under uniaxial tension. To confirm these formulas under other stress fields, the mechanical and optical behavior under biaxial and uniaxial compression of cellulose acetate was investigated precisely in this work. As a result, the yield stress and the yield fringe order under uniaxial compression were expressed by the same equations under uniaxial tension. Moreover, the uniaxial compression stress-strain-fringe order relations were represented in the same nondimensional forms under uniaxial tension, regardless of both strain rate and temperature. Similarly, these biaxial relations were obtained by substituting simply the difference of the principal stress and the difference of the principal strain into the stress and the strain in the uniaxial relations, respectively.

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The process of delayed fracture of cathodically charged quenched and tempered SNCM 8 steel specimens has been studied with a special emphasis on the examination on the characteristics of the morphology of crack propagation. The delayed fracture process in this experiment can be reproducible by a combination of the static fracture tests with controlled strain rates and specimens cathodically charged prior to loading. The characteristics of the morphology of the fractured surface of a delayed fractured specimen are associated not only with the interaction between hydrogen behavior and microstructures but also with the macroscopic strain rate which affects the preference of crack path, i. e., an intergranular or transgranular manner.

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A study was conducted on the effect of crack size or surface roughness on the tensile strength of ceramics used for lower quality fueled gas turbine or diesel engines. In general, in order to remove surface defects or to form the correct shape, ceramic materials have been machined at great cost and with much waste of time. Even if the materials were carefully machined, their surface would be attacked, with considerable damage, by corrosive ashes. The experimental results show that in the case of partially stabilized zirconia at 650°C the existence of artificial corrosive ash containing vanadium pentoxide and sodium sulphate on the flaws significantly enhances their tensile strength. However, in case of silicon carbide at 900°C, no remarkable difference could be found between the results with and without corrosive ash where the hardness indentation method was used as a quantitative tool to simulate mechanical surface defects.

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It is well known that when a curved beam is subject to bending, the shape of its cross section is flattened and collapse occurs as the rigidity is reduced. It is important for design determine their nonlinear behavior. This paper describes the elastic-plastic large deformation analysis of a curved beam with a thin walled cross section by the finite element method. The analytical formulation is developed by extending the kinematic work hardening model preposed by Ziegler. Several representative cases are computed.

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Sink marks that occur on the outer surface of fiber-reinforced composite materials pose a problem because they lower the quality of a product. Various studies have been conducted on material composition, molding methods and shape factors in an effort to find effective methods of preventing sink marks. In this work, the mechanism causing sink marks have been investigated through numerical analysis and experimentation. The aim of this investigation was to find the optimum molding method and shape factor that would minimize sink marks on a sheet molding compound (SMC) The result makes it clear that sink marks are most likely to occur in the final process of anisotropic flow. Further, it is now possible to explain analytically the various factors that facilitate the molding of vehicle parts with excellent surface quality.

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In order to develop the shape memory alloy engine, basic output power characteristics of a twin crank heat engine are investigated. As a shape memory alloy, TiNi alloy wire with outer diameter 0.75 mm is used. The material is heat-treated to memorize the shape of a helix. The results are summarized as follows. (1) The output power of the engine increases with hot water temperature. Rotational speed where the output power is maximized shifts toward higher speed. (2) The maximum output power increases with hot water temperature. The increasing rate of the power decreases above a certain hot water temperature. (3) The output power increases as deformation of shape memory alloy helix large.

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