[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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From the observation of the fatigue crack growth behaviors and fractographs, the short glass fiber reinforced polyvinyl chloride with Sn series stabilizer was seemed to be anisotropic little and ductile, and the fiber reinforced polyvinyl chloride with Pb series stabilizer to be anisotropic and brittle during stable crack growth, though the mechanical properties of two kinds of fiber reinforced polyvinyl chlorides were anisotropic. It was found that the configuration of fatigue fracture surface ralated to the constants m and C values in Paris' Law, and the fatigue crack growth behaviors were influenced by the adhesive property between fibers and matrix resin due to the stabilizer.

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The interaction of crack growth in hybrid bodies subjected to cyclic loading is investigated using the coupled compact tension specimens model. coupled CT specimens of 0.45% C steel, JIS S45C and aluminium alloy, A2017-T4, individually precracked to their lengths, are loaded by common pins in the grip of a fatigue machine. The crack propagation behaviour of coupled specimens fatigued under a stress ratio of 0.7 is compared with that of single specimens. The interaction curve for coupled hybrid specimens is theoretically predicted and the interaction law is discussed. the proposed interaction principal, which is on the basis of the distribution of the total elastic energy release rate in coupled specimens, shows good agreement with experimental results compared with the method by Marek, based on the maximum energy release rate.

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The characteristic properties relevant to fatigue design, the high-cycle fatigue strength, the cyclic yield stress, and the crack propagation rate were obtained for a high strength powder metallurgical (PM) steel varying in five density levels. The fatigue limits σ_w and the cyclic yield stress σ_ys decreased as the porosity content increased. As the density decreased, the ratio of fatigue limit to tensile strength, σ_w/σ_B, decreased from 0.29 to 0.21, while that to cyclic yield stress, σ_w/σ_ys decreased from 0.50 to 0.29. Thus, the latter ratio was more sensitive to density or prosity content. The crack propagation rates depended strongly on density : the two orders of magnitude differed between the highest-density steel and the lowest density steel. However, these were expressed in a unified form normalizing ΔK by Young's modulus E and multiplying da/dN by a factor defined as l/(l-d), where d is the mean diameter of pores and l the mean inter-pore distance measured in an arbitrary cross section. Based on the unified crack propagation rate, the S-N curves of the PM steels were successfully predicted using an elastic plastic fracture mechanics analysis.

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Fatigue crack growth and closure were investigated in both SUS304 stainless steel and SM41A steel at elevated temperatures up to 500°C°C. A quantitative analysis was made of the roughness and oxide of the fracture surface at the near-threshold region. The effects of the roughness and the oxide on the fatigue threshold behavior were examined. The value of the threshold stress intensity factor range increased with increasing test temperature in both steels. An extra crack closure was not observed at elevated temperatures in SUS304 steel, although fracture surface roughness increased significantly with increasing test temperature. On the other hand, an elevation in the crack closure level was observed in SM41A steel due to the effect of the oxide products on the fracture surface at elevated temperatures. It was found that oxide-induced-crack-closure played an important role in effecting the crack closure at elevated temperatures, while roughness-induced-crack-closure had a less important effect on crack closure at near-threshold.

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The near-threshold fatigue crack growth behavior is investigated for carbon steel (S25C), low alloy steel (SM50B), stainless steels (SUS430, SUS304 and SUH310), nickel alloy (Hastelloy X) and aluminium alloys (A2017 and A5083) in laboratory and dry air conditions. At higher load ratios, such as 0.8, where there is no closure, ΔK_th-values are proportional to Young's modulus, E. At lower load ratios, such as 0.1, however, ΔK_th/E-values are dependent on material and atmosphere, due to crack closure. Oxide-induced closure appears on carbon and low alloy steels in laboratory air, while oxide-thickening within the crack is prevented by passive film on stainless steels, nickel alloy and aluminium alloys. Dry air reduces oxide formation on the fracture surface. Roughness-induced closure is stronger in nickel and aluminium alloys than in steels. Fracture surfaces are more crystallographic in the former alloys. Phase-transformation-induced closure results from martensitic transformation inherent to austenitic stainless steels. This transformation, however, opens the crack near the threshold rather than closes it.

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Fatigue cracks growing perpendicularly to the interface of dissimilar materials often arrested or branched at the interface, This branching crack phenomenon seems to be important to improve the fatigue life of composite material or to evaluate the fatigue life. In this paper, the branching crack phenomenon is investigated in detail using epoxy dissimilar plate specimens with various Young's modulus ratios (E₂/E₁) and different bonded strengthes. It is found that the branching crack along the interface can occur in only limited conditions. That is, Young's modulus ratio E₂/E₁ is higher than 1.14 and an applied displacement range ΔV (or load range) is higer than a critical value, which becomes large with increase of E₂/E₁ and becomes lower in the case of iow bonded strength. A new model to explain these branching crack phenomenon is proposed and discussed based on linear fracture mechnics.

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Fretting fatigue damage formation of carbon steel S45C has been examined using interrupted fretting fatigue tests, which consist of two-stage fatigue loading, i.e., the first stage is fatigue loading with fretting under one of the stress ratios R=-1, 0, 0.33 and 0.5, and the second stage is fatigue loading without fretting under R=0.5. The minimum number of cycles, N_cr, in the the first stage which caused rupture in the second stage was 7.5×10⁴, and was independent of R. The damaged layer at N_cr was about one grain size, and was hardened due to the formation of fine cell structure. It was concluded that the fretting fatigue damage is formed in the early cycles of fretting fatigue, and does not depend on R.

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The notch effect on corrosion-fatigue strength was investigated for high-strength steels of HT50 and HT80. In ion exchanged water, the fatigue strengths of HT80 were not affected by slight notches, and then decreased with an increase of α_k (stress concentration factor). When α_K was further increased, they reached a value which is probably the corrosion-fatigue strength of the circular cracked test pieces. For HT50, the fatigue strength decreased from slight notches, and the strength of a sharp notch coincides with that of HT80. In synthetic sea water, the fatigue strength was considerably lower, and was independent of the materials. However, a similar notch effect was obtained. This behavior can be explained from observations of the surface and the cracks of test pieces.

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The line-spring model developed by Rice and Levy has proven to be an effective tool for evaluating stress intensity factors in surface-cracked plates. Application of the model, however, has been restricted to problems of static loading conditions. In this paper, the dynamic line-spring model is newly constructed to obtain an approximate dynamic response of a plate containing a surface crack. For an example of the application of the present model, the dynamic response of a plate which contains two semi-elliptical surface cracks and is subjected to a uniform vibrating loading at each end of the plate is analyzed. The dynamic stress intensity factor is calculated for the frequency of vibration along the crack front of the surface crack. It is observed that the dynamic stress intensity factor increases rapidly near the resonance frequency of the surface-cracked plate, which is lower than that of a uniform plate.

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Crack tip blunting in ductile material was analyzed under a small-scale yielding subject to mixed mode loadings of Mode I and Mode Ii. The material was assumed to be an elastic perfectly-plastic solid with Poisson's ratio being 1/2. The slip line field for a sharp crack under mixed mode loading was first determined by means of elastic-plastic finite element analysis. It was shown that only one elastic sector exists in the vicinity of the crack tip differing from the possibility of the existence of two elastic sectors discussed by Gao. The result for the sharp crack obtained was used as the boundary condition for the analysis of crack tip blunting. The characteristic shape of the crack tip blunting was obtained, which is just like the tip of a Japanese sword. Also, the stress field was determined around the blunted crack tip.

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Fracture toughness characterization in the transition region is examined for two low alloy steels focusing special attention on the fracture modes, cleavage mechanism and ductile tearing. Fracture toughness tests were conduced over the regions from transition to upper shelf using compact specimens. In the transition regime, a crack may initiate and grow some amount by ductile tearing followed by brittle fracture by cleavage. The fracture toughness, J_in, at the initiation of the ductile tearing tends to decrease with a reduction in test temperature, and the scatter in J_in, as well as the amount of stable crack growth, Δa, at the onset of the brittle fracture becomes more remarkable. Generally, Δa decreases as J_in decreases. It should be noted that these characteristics should be taken into consideration in developing a new explanation for the fracture toughness behavior in the transition region.

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The behavior of a geothermal reservoir connecting with a horizontal natural fracture in the earth's crust is analyzed on the basis of liner elastic fracture mechanics. Noting crack reinitiation from preexisting micro craks of a natural fracture, the influence of various factors on the behavior of the reservoir is investigated, and then the stability of reservoir is discussed. It is revealed that the main factor governing the mechanical behavior of the reservoir is the discontinuity of tectonic stress and fracture toughness across the natural fracture. It is also shown that the reservoir is always stable and can be relatively larger than a vertical reservoir in a continuous rock mass, when the horizontal compressive stress in the region over the fracture i s larger than that in the region beneath the fracture.

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Methods are proposed for distinguishing the mode of deformation and for evaluating the size, and orientation and location of fluid-filled cracks in the earth's crust which can be potentially used as a reservoir in geothermal heat extraction. The basic concepts of the method are obtained by studying the nature of the elastic waves radiating from the cracks during crack growth. here, based on the two-dimensional elastodynamic theory, the problem of the dynamic crack growth is analyzed with the aid of integral equations defined in the Laplace or Fourier image space, where the dynamic crack growth is modelled by releasing tractions on the small interval just ahead of the crack tip.

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Material characterization of SUS316HTB, used as boiler superheater for long time under service operating conditions, were performed by means of the Charpy impact test, the short term creep test, hardness measurement and metallographic observation. The formation of brittle sigma-phase mainly along grain bounaries is a principal cause of material degradation, in cooperation with carburization from the fire side of superheater tubes. The supporting evidences for the formation of brittle sigma-phase along grain boundaries is I.G fracture caused by the Charpy impact test (R.T 77K) and by the creep test applied to the materials used. The Larson-Miller parameter is a useful tool for examining the effect of sigma-phase formation on various materials used in service under different conditions in operating temperature and periods. L. M. P of 22 may be a critical value for which more detailed material characterization is needed to determine the replacement time for superheater tubes. In order to verify the above approach, an appropriate estimate or direct measure of the temperature of superheate tubes is crucial.

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In order to evaluate the fracture toughness of structural steels for superconducting magnets of fusion reactor, elastic-plastic fracture toughness testing was performed at 4.2K on AISI 310S base metal, weld metal and 20Mn steel. Fracture toughnesses were evaluated by a single specimen technique using the Key Curve reported previously. Elastic-plastic fracture toughness J_IC and tearing modulus T_mat of weld metal were significantly lower than those of base metal. As the result of AE measurement, microfracturing was detected at the early stage of loading, and pop-in cracking was observed at the later stage. Fractographic and metallographic examination of fracture surfaces and fracture paths revealed a difference in dimple sizes between the weld metal and the base metal, and also micro void formation ahead of a growing crack tip, which resulted in smaller crack opening angle of the weld metal than the base metal. Finally, the significance of crack growth analysis of weld metal was emphasized to ensure the structural integrity of superconducting magnet.

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The present work tackles the transient thermoelastic problem for an infinite solid with an external circular crack. It is assumed that the transient thermal stress is set up by the application of heat exchange by convection on the crack surfaces. By use of the finite difference method for the time variable only, the analytical solution for spatial variables can be obtained. The numerical results are shown for the temperature and stress intensity factor.

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The formulation is the so-called "orders of scattering" approach with the translation of wavefunctions expressed in one local coordinate system to those of another. The scattered waves for incident plane harmonic pressure waves are expressed as an infinite sum of various orders of scattering. An exact steadystate solution is derived for the scattered radial stress, which is also the power spectra of scattered pulses due to the impulse incident. Further, the solution is simplified for the case of far field backscattering. The power spectrum, ranging from 0-6MHz, is calculated for various geometrical parameters of the problem. Spectral features are explained with 3-D graphic representations. In concluding remarks deduced from the graphics, the increase of center to center separation of two cavities makes the periodicity of scattering intensity distribution short. Abrupt diminishes of intensity are caused at resonant frequencies of the cylindrical cavities containing acoustic fluid.

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This paper presents an analysis of the dynamic stress in a solid disc subjected to cyclically varying rotations with respect to time, that is, Ω^^-(t^^-)=Ω^^-₀+Ω^^-₁sin(Ω^^-₂t^^-) (Ω^^-₀, Ω^^-₁, Ω^^-₂: constants). The radial displacement and stress components are derived from a general solution for a solid disc, whch was obtained previously by the author. A dynamic solution leads to the existence of two kinds of resonance circular frequencies. For Ω^^-₁≠0 and Ω^^-₀=0, the resonance circular frequency Ω^^-₂ agrees with a half of λ_n which corresponds to the eigen-circular frequencies for in-plane vibrations of rotating discs. For Ω^^-₁≠0 and Ω^^-₀≠0, Ω^^-₂ agrees with both cases, λ_n and λ_n/2. It is finally discussed how the circular frequency Ω^^-₂ has influence on the stress components and their distribution.

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The deformation and strength of tapered lap joints having different thicknesses of adherends were investigated both analytically and experimentally. The strain distributions of the joints of carbon steel bonded with epoxy resin under tensile shear loads were analyzed by the finite element method. The analytical strain distributions coinsided approximately with the experimental results. The strength of tapered lap joints was determined by using the strength laws of adherend, adhesive resin and adhesive interface. The results were compared with the experimental strength of the joints. Initial cracking in the joints did not lead to a final fracture and the joints were able to carry the increasing load. It was shown that the tapering of the adherends was effective in improving the strength of the asymmetric single lap joints.

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In the previous paper, we invented the method to separate principal stresses by using only the isochromatic fringe patterns. In the present paper, by using this method, we propose an automatic stress analysis system by photo-elasticity. This system is composed of the photo diode, the amplifier, the A-D converter and the computer. The analogue information on the isochromatic fringe patterns is coverted to the digital one by the photo diode, the amplifier and the A-D converter. Thus, by using the microcomputer involved the program to separate the principal stresses, we obtain the stress distributions from these digital data of the fringe patterns. We apply this system to obtain the stress distributions of the circular and square plates subjected to concentrated loads, and show that the stresses obtained by the present system are in good agreement with those calculated theoretically or given by Frocht.

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The large deflections of a fiber-reinforced straight beam is analysed in the framework of the theory of ideal fiber-reinforced composite materials. The beam is reinforced in the axial direction and simply supported at its ends. It is subjected to uniform pressure at the lateral surface as well as at the ends. Universal solutions are obtained and the results for a linear elastic response are shown in figures.

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Plastic deformation of metallic material with elliptic inclusion is studied using the rigid-plastic finite element method. A plane model of material with inclusions is assumed. The effects of the aspect ratio, the yield stress ratio and the volume fraction of the inclusions on the deformation behaviour are studied. It follows that the deformation mode is much affected by the aspect ratio of the model. The relation ship between the deformation mode and the applied stress necessary for the deformation is discussed. The effect of crystal slip is also studied by incorporating the Bishop-Hill theory of crystal slip into rigid-plastic finite element analysis.

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The interference effect of double-edge cracks of equal length on the plane-strain limit moment is analyzed based on the lower bound theorem. The magnitude of the reduction of the limit moment and the crack pitch range, within which the limit moment is reduced by the interference effect, can be predicted by the theory. The crack pitch range influenced by the interference effect is approximately equal to the height of the specimen when the crack length-to-specimen height ratio is less than 2/7, and in the range from 2/7 to 1, decreases linearly with increasing crack length. Theoretical results are compared with the experimental results. Good agreement is obtained between theory and experiment for the magnitude of the reduction of the limit moment and the crack pitch range influenced by the interference effect.

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Quenching cracks are generally considered to occur under united thermal and transformational stresses. This paper deals with some of the quenching effects on cracks and the hardenability of a steel bar (SUJ2 and S45C) by polyethylene glycol (PEG) solutions. PEG of various molecular weights were prepared for the quench cooling solutions. The cooling rates of silver test pieces were closely related with the viscosities of solutions of various contents of PEG, and the controlled cracks and hardenabilities of steel. Also, the residual stresses caused by quenching were measured by the X-ray diffraction method. A considerable tensile stress and a relatively smaller compressive stress existed on the surface area and in the neighborhood of the center, respectively. The sensitivity of the cracks could be explained clearly by the quench cooling rate.

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Shape determination method of structures based on the Inverse Variational Principle is extended to the multiple loading case. Given several sets of loads which are not active at the same time, such a shape is determined that makes the weighted sum of the potential energies for each load set stationary with the constraint of the volume constancy. The problem has the same form as the multiobjective optimization one. The Pareto optimal solutions can be obtained easily by the Energy-Ratio-Method proposed in the single loading case. It is observed through numerical examples that in the Pareto optimal structures, stress levels under each set of loads are relaxed somewhat compared with the worst case. If the weight to each loading case is taken as the probability that the load is actually active, then the obtained shape is interpreted as the one that will yield the highest expected value of the potential energy among the shapes with the same volume.

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This paper presents the theoretical results of the stresses in a coil spring of arbitrary cross section. The analysis consists of two parts one of which is concerned with the displacements, the angles of rotation, the resultant forces and the resultant moments which occur in a helical spring during the loading. The results in this problem are derived by application of the curved beam theory in which all displacements and all forces in three orthogonal directions of the coil spring are included with consideration of constraints of the edges of the spring. At the second step, the paper presents the expressions for stresses in the spring due to the compression in the direction of the axis of the cylindrical spring when both edges are kept to be parallel during the deformation by use of the author's results given in the preceding paper (1st report). Numerical calculations have been carried out for four cases of a circular cross-section spring, an elliptical cross section spring, a rectangular cross section spring and an oval section spring.

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Impact tensile experiments were carried out for cracked steel specimens at -196°C, to make clear the critical condition for the growth of a crack. when impact tension was imposed on a specimen superposed on a static tension σ_s, impact stress σ_d did not depend on σ_s in the lower range of σ_s but decrease in the higher range of σ_s with increase of σ_s for the fracture. The similar relation between σ_s and σ_cd was smaller for shorter specimen than that of longer one. According to the investigation on the fracture surface by SEM after impact or static experiment twin was not always observed. Studies on the distribution of dislocations by TEM, and on lattice distortion by X-ray diffraction method, near a crack tip after fracture shoed the presence of more complicated and larger microscopic distortion in the case of impact fracture.

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The fatigue crack growth behavior in austenitic stainless steel, SUS316, under repeated impact loading was investigated by means of fracture mechanics. The crack growth rate of a solution heated specimen was greater than that of an annealed specimen for both non-impact fatigue and impact fatigue. The effect of impact velocity on the crack growth rate depended on the K_max level. The crack growth rate during repeated impact loading was greater than that in the sinusoidal stress wave. The fracture appearance at a low ΔK level was structurally sensitive modes, like intergranular cracking, regardless of repeated impact and sinusoidal loading. The dominant fracture appearance at a high ΔK level during repeated impact loading was the ductile mode, like striation.

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The longitudinal waves in a viscoelastic rod of finite thickness are studied, taking into account the effect of radial inertia. The equation of motion used in this work is an application of the Love-Rayleigh theory for an elastic rod. An analytical solution of the transient response is obtained to examine the influence of radial motion on axial strain-time history. In addition, the attenuation and dispersion characteristics in the frequency region are discussed. Some experiments are performed on polymethyl methacrylate (PMMA) specimens with the view to evaluating the adequacy of the equation of motion. It is found that the theoretical predictions provide reasonable estimations of the strain-time history as well as of the attenuation and dispersion properties.

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