[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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[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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This paper is concerned with the influence of notch root radius at the weld toe and TIG treatment on fatigue properties of welded high strength steel. In general, it has been considered that small notch radii at the weld toes are responsible for low fatigue strengths of welded joints. However, fatigue limit of a welded joint usually does not depend on the notch root radius of the weld toe becauce of the existence of non-propagating crack. In most cases, fatigue limit of the welded joint is determined from the notch root radius at the branch point which is a material constant. The beneficial effect of TIG treatment on fatigue properties differs according as the value of mean stress. This result is explained from the characteristic fatigue behavior of notched specimens.

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The torsional fatigue tests were performed using annealed or pre-strained 0.21%C steel specimens under constant and two-step stress amplitudes. The behavior of the fatigue cracks was observed successively on the specimen surfaces by the replication method and the characteristics of the torsinal fatigue cracks were examined. Torsional fatigue cracks tend to branch off. Under a constant stress amplitude, the rate of change in crack growth rate varies with the phenomenon of branching. Under two-step stress amplitudes, Miner's rule holds approximately on the annealed specimens but the rule does not hold on the pre-strained specimens.

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Influences of stress wave form and the superposition of vibratory stresses at maximum stress under low frequency varying load on cyclic SCC crack growth behavior have been investigated on a high-strength Al-alloy, and the loading condition dominating over cyclic SCC and the competition of cyclic-and dynamic SCC have been discussed. The threshold stress intensity factor for cyclic SCC K_max=K_FSCC is independent of hold time at maximum stress but increases with a decrease of varying load rate versus time K. At higher ΔK_eff, however, da/dN accelerates with a decrease of ΔK_eff, i.e., at longer rise time, and it is similar to that of conventional corrosion fatigue. On the other hand, the superposition of vibratory stresses promotes corrosion-products induced wedge effect, with K_op=K_max. In this case, K_FSCC is determined by the threshold stress intensity factor K_DSCC for dynamic SCC that is corresponding to secondary loading condition.

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The behaviors of small fatigue cracks in annealed and pre-strained 0.45% C steel specimens were investigated in order to clarify the effect of macroscopic yielding on the growth law of small cracks. The growth laws of small cracks can be expressed in the same form of dl/dN=Cσ_aⁿl for the above two types of specimens. The macroscopic yielding or pre-strainning causes the change in the values of n (n=8 for not yielded specimens and 6.4 for pre-strained or yielded specimens) and the independency of stress ratio in the growth law of small cracks.

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This paper is concerned with the beneficial effects due to additional holes or indentations. Two indentations facing each other with the tip of a crack is especially effective in retardation of crack propagation. The effects of the indentations can be estimated approximately from the existence of residual stresses produced by the indentations.

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Fatigue crack growth characteristics in commercially pure titanium have been studied using SEN sheet specimens under push-pull loading with stress ratios ranging from -1 to 1/3. Crack closure has been investigated by monitoring the electric potential using a DC-potential drop method. A load level vs. electric potential curve showed a fairly sharp bend during increasing a load level within one load cycle. The load at this bend has been identified to the crack tip opening load by examining the crack profiles using a two-stage replica method. Crack closure was observed to occur at every stress ratios except at R=1/3. The exponent m for the crack growth relation da/dN=C (ΔK)^m was about 3 for the cracks longer than 1 mm. Crack growth rates for cracks shorter than about 1 mm and at R=-1 were fairly higher than those expected from the relation for longer cracks.

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This paper is concerned with the dynamic fracture criterion of cracked plate which is made of epoxy resin. A tensile pulse wave is generated by an impact apparatus and travels through the cracked plate away. The behavior of stress wave in the plate and the crack propagation phenomenon are analysed by the photoelastic technique using the high speed camera. The dynamic finite element method is also used to find the fracture criterion from these results and moreover the formula on the dynamic stress-intensity factor of this model is proposed.

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This paper treats a transient thermoelastic problem in a thin plate with a Griffith crack perpendicular to the surfaces of the plate. It is assumed that the transient thermal stress is set up by the application of the heat exchange by convection of the surfaces of the crack and plate. By use of finite difference method for time variable, an analytic solution for spatial variables can be obtained. The numerical results are shown in figures.

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The present paper deals with the tensile strength and fracture mode of SiC fiber subjected to the exposure of hydrostatic pressure, isothermal heating and liquid aluminum environment. The conditions are sometimes encounted in FRM fabrication by a liquid infiltration method. The results showed no fiber degradation for a given isothermal heating and hydrostatic pressurizing, but the decrease in the fiber strength for the liquid aluminum environment with the exposure time. The fractgraphic observation proved to be as follows. As for the original fiber, the isothermally heated fiber and the hydrostatically pressurized fiber, the cracking occurred from the inner defect of the fiber or from the surface defects. In general, the fiber with the inner defect is stronger than the fiber with the surface defect. For the liquid aluminum exposed fiber, the numbers of fiber that the fracture originates from the reaction product on the surface, increase as the exposure time increases, at the same time, the tensile strength gradually decreases.

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Adiabatic elastic constants for aluminum are calculated by a pseudopotential method in various atomic volumes, which are corresponding to any pressure and temperature. Temperature dependence of ideal strength and surface energy are evaluated from stress-strain relation in <100> deformation mode up to fracture strain. Using Lindemann's law, pressure dependence of melting point is also evaluated from elastic constant C_ll at melting temperature and is compared with existing experiments. Finally, a method to obtain isothermal elastic constants are discussed by using Gruneisen parameter defined for <100> deformation.

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The fracture behavior in bending of notched bars of polycarbonate, polyvinylchloride and polymethyl methacrylate has been investigated. The uniform bending tests of single edge notched plates that are thick enough to yield in plane strain have been carried out for a wide range of notch radii. The experimental results were discussed in terms of the critical maximum stress and the notch root radius. The main results obtained are as follows : (1) The predominant factors for determining the ductile-brittle transition of fracture mode in bending are the notch root radius and thickness of specimen. (2) The critical maximum stress for brittle fracture is governed by notch root radius alone in the case of a constant thickness of specimen. (3) The fracture criterion of notched bar mentioned above, is commonly applied to both tension and bending, and the criterion holds in three kinds of rigid plastics.

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Vibrational tests provide the most direct means of obtaining the mechanical properties and evaluating the fixation function of mechanical elements involved in the pseudoelastic materials such as NiTi shape memory alloy. The tests are applied to uniaxial deformation and canti-lever conditions whereby the appropriate constitutive equation in given by the rate type equation.

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Relaxation tests provide the most direct means of obtaining the mechanical properties and evaluating the fixation function of mechanical elements involved in the pseudoelastic materials such as NiTi shape memory alloy. The tests are applied to uniaxial deformation and canti-lever conditions whereby the appropriate constitutive equation like Malvern Equation is given by the rate type equation.

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When shape memory alloys, such as Ni-Ti, Cu-Al-Zn are loaded, after initial elastic deformation, inelastic deformations sets in due to stress induced martensite transformation. To examine impact characteristics of NiTi, a high speed compression testing system using split Hopkinson pressure bar was developed. Specific examples of interaction between the stress induced and temperature induced martensite and the associated rate effect are presented for NiTi, based on the statistical continuum theory of martensite mechanics. Through these studies, the elastic modulus, the solid viscosity and the effect of temperature on mechanical characteristics of NiTi are clarified.

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An attempt has been made to estimate the indentation cracking process from the information of acoustic emission monitoring. The relations between crack propagation velocity and acoustic emission threshold in terms of double torsion testing were first investigated. The results indicated that the crack propagation velocity was approximately proportional to the acoustic emission rate. These relations were applied directly to the analysis of the indentation. Various loading speeds and loading levels were selected. Assuming that the radial crack with semi-circular only occurs during indentation process, the crack length should be given as a function of the acoustic emission rate. From the results of calculating the extent of crack propagation obtained by the acoustic emission counts for the indentation, good agreements were obtained between predicted and measured crack length. Fracture toughness values obtained by these testings were also compared.

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The stress distribution in threaded portions of bolt and nut being fastened by applying torque to nut is analysed by FEM. The object of analysis is composed of a bolt, a nut and a fastened plate, which are all treated as axi-symmetric bodies. Two methods of analysis are proposed. The first method is composed of the axi-symmetric analysis for the state generated by applying tension to bolt and the analysis of torsion for the state generated by applying distributed torque at the contact surfaces. The distributed torque is approximately estimated from the distribution of the normal stress generated at the contact surfaces by the axial tension. The second method is a three-dimensional analysis, where effects of lead angle are considered only through the relationships of forces acting on the pressure flank. From some calculations by the above two methods, effects of the torque applied during fastening on the stress distribution is estimated.

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A Small-scale boundary solution system for the classical St. Venant problem with prismatic beams of arbitrary cross section is presented in this paper. Since the problem can be resolved into four trunk problems related to basic loading states, the entire solution is assembled with each solution. Each trunk problem can be dealt only with respect to the boundary of cross section, which simplifies the data structure required for computation.

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Tearing instability crack growth in low alloy steels was evaluated in a regime of elastic plastic fracture mechanics by use of recrystallization-etch technique. Specimen geometries used here were standard compact and 3pt bend specimen, and 4pt bend type specimen having a part-through surface crack. In order to produce high compliance for a testing machine, disc springs were used where the compliance changes from 1kN/mm to 5kN/mm. After the fracture experiments the crack tip strain energy dissipation rate dW_p/da (W_p : crack tip strain energy absorbed within the intense strain region, a : tearing crack extension) was determined by the recrystallization-etch technique. It is shown that the value of T_w (tearing modulus based on W_p) is constant before and after an onset of tearing instability. In the surface crack specimen, three dimensional profile of the intense strain region along the crack front was observed. This experimental results indicate that the T_w criterion is applicable to the crack extension from the surface flaw, although a singular extension behavior of the intense strain region was observed only near the specimen surface.

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In order to investigate the effects of rolling ratio and specimen orientation on the fracture toughness of thick rolled steel plate, elastic-plastic fracture toughness tests were carried out. A thick rolled steel plate initially 75mm in thickness was sliced along the rolling direction into three pieces and two of them were reduced by hot rolling to 38mm and 19mm. All the specimens with orientation TS or ST were collected in the thickness plane of each rolled plate. Fractographic observation such as stretched-zone width measurement was conducted as well as R curve determination. The results obtained are summarized as follows. (1) Both rolling ratio and directionality influenced the fracture toughness. The fracture toughness was higher for the TS specimens than for the ST specimens. This trend was intensified with increasing rolling ratio. (2) Critical stretched zone width also showed dependency on the two factors mentioned above. Elongated MnS inclusions induced difference of micro- and macroscopic fracture appearances.

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An automated system for a rapid and precise X-ray stress measurement using a personal computer is developed. The block diagram of the system and a flowchart for the stress measurement method are described. Of the various method, the method most suitable for the material measured can be programmed in this system. The residual stress in a hardened steel having a broad diffraction line (half-width of 7.2°) could be measured in six min with a small standard deviation of 13 MPa by the Gaussian curve method using the sin²ψ method. Both the oscillation method and the fixed ψ method using the Gaussian curve method allow the X-ray stress measurement of coarse-grained steels ; the sin²ψ diagram obtained by these methods showed a good linearity. The residual stress measurement of an annealed chromium powder gave almost zero stress values, -3.2 to 2.9 MPa depending on the method used, showing a high accuracy of the system.

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Rotating bending fatigue tests are carried out to evaluate the notch sensitivity of three kinds of age-hardened aluminum alloys, 7075-T6, 2017-T4 and 6061-T6. In case of a blunt notch, the notch sensitivities of three age-hardened aluminum alloys are nearly equal to each other. In case of a sharp notch, notch sensitivities decrease in the sequence 7075-T6, 2017-T4 and 6061-T6. The notch root radii ρ_o at the branch points of 7075-T6, 2017-T4 and 6061-T6 are 0.1 mm, 0.2 mm and 0.4 mm, respectively. The above stated phenomena are caused by the differences in the crack growth resistances related to crack topography.

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The relief of surface residual stress in an FC25 pearlitic graphite cast iron plate has been experimentally studied under impact loading. Surface residual stress is relieved by impact repeated more than one hundred times. When the impact loading stress wave amplitude added to the residual stress is more than 0.025% offset stress in the materials, more residual stress is relieved. When the value is smaller than the added value, residual stress is not relieved. After the relief of surface residual stress under impact loading, the fatigue limit on the FC25 pearlitic graphite cast iron cannot be improved more than before, and remarkable change in residual stress was not observed after exposure in open air for one month.

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A procedure for the analysis of buckling of axisymmetric liquid storage tanks subjected to static lateral load is proposed. The procedures based on the expansion of local buckling mode using vibration modes calculated by FEM considering the effect of initial stress. Calculated natural frequencies of water-filled Al tank and buckling loads of empty or water containing polyester tanks under lateral end load are compared to experimental results. The comparisons show good agreement. During vibration tests of the water-filled Al tank using shaking table, two buckling modes were observed. The first is local elastic buckling at lower part of water level caused by negative pressure from water-shell interaction. The second is diamond buckling at fixed end. The first is simulated applying the pressure in static. Calculated buckling mode is very similar to observed one by high speed camera. The second is evaluated by the classical buckling stress.

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Inelastic post^buckling behavior of perfect columns is numerically analyzed by taking account of the reversed plasticity which may appear in the convex side of the column following elastic unloading. A numerical method analyzing post-buckling behavior is developed for a discrete column model composed of rigid bars and nonlinear spring elements. A power type stress-strain relation is assumed for the column and it is associated with three types of unloading and/or reversed loading material response, i.e., the perfectly elastic unloading, isotropic and kinematic hardening rule. The load-deflection curves in the post-buckling range are calculated for pin-ended perfect columns with an asymmetric cross section. It is shown that the reversed plasticity affect a little the maximum load but it lowers significantly the load-carrying capacity after the maximum load.

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Coiled springs are sometimes subject to lateral and longitudinal, namely oblique loads. Some authors investigated the deformation of springs under oblique loads by the linear finite deformation theory. However the nonlinearity increases as the longitudinal load increases. In this paper the deformation of the coiled spring under the oblique load is studied with the nonlinear large deformation theory. The coiled spring is remodeled as a single thin rod. Rigidities of this thin rod have the features of the coiled spring and after deformation these rigidities vary along the axis gradually with the change of the pitch of helix. The lateral stiffness coefficient is derived as the function of not only longitudinal but also lateral loads. The difference between the present and conventional results of the lateral stiffness coefficient becomes large as the longitudinal load closes to the critical lateral buckling load. These effects are attributed to the nonlinearity of the large deformation of the spring.

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Friction coefficient, relative slip amplitude (fretting amplitude) and dissipation energy per one fretting cycle for steel ball-PMMA (polymethylmethacrylate) in fretting situation are investigated under various levels of normal load and amplitude of steel ball. Friction coefficient increases and relative slip amplitude decreases with fretting cycles in this study. Especially, dissipation energy per one fretting cycle was calculated by inputting a friction force and a relative displacement to a microcomputer. Equations between a tangential force and a tangential displacement based on the theory of elasticity were made by using the results of Mindlin who analyzed the contact of two elastic balls. It was shown that the experimental results of dissipation energy can be explained by these equations.

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The fatigue-crack-initiation life N_c and the total fatigue life N_f of S45C specimens having a wide range of notch geometries were investigated in the rotating bending fatigue tests. The experimental data were discussed on the basis of the concept of "linear notch mechanics" proposed recently by one of the authors. N_c is determined mainly by the maximum elastic stress repeated at a notch root σ_max and the notch root radius ρ alone, irrespective of the notch depth t. On the other hand, N_f is determined mainly by σ_max and ρ alone, except the case of a shallow notch (t=0.1 mm). This is because σ_max obtained from the elastic calculation and ρ control the elastic-plastic behavior near the notch root.

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Saint-Venant's end effects to composite materials are frequently different from those to isotropic and homogeneous materials, therefore, the estimation of its effects is an important subject in relation to the evaluation of strength of composite materials. This paper is intended to establish the general method to estimate this Saint-Venant's end effects to composite materials, and the contents are as follows: (1) The finite element formulation to estimate Saint-Venant's end effects is established using the principle of virtual work and some example problems of laminate media are analysed by deyeloped method. It is shown, through these analyses, that the newly-defined characteristic length l_e is useful to evaluate the rate of attenuation of non-uniform local stress distribution. (2) The conventional elastic-plastic finite element analyses are carried out to the same examples, and the availability of developed method is confirmed. The end effects in case that plastic deformation occurs, are also discussed.

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The stress fields caused by plastic strain can be replaced by the sress fields due to pairs of forces. Based on this consideration the body force methed proposed by Nisitani for elastic problems was extended to the analysis of the elastic-plastic problems. The solutions are obtained by superposing the stress fields of a point force and a pair of point forces so as to satisfy a given boundary condition and the constitutive equation. The method of solutions was illustrated, by taking an example of the elastic-plastic problem of an infinite plate with circular hole subjected to internal pressure.

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To find the effect of variation in strain amplitude on the strain accumulation characteristics in the mechanical ratcheting of a carbon steel, a thin-walled tubular specimen was subjected to strain-controlled cyclic axial load and internal pressure. When the cyclic load with a constant strain amplitude Δε^^-₁ was superposed upon the internal pressure, the strain ε^^-₂ accumulated in the circumferential direction was formulated by the following equation as a function of the steady circumferential stress σ^^-₂ and number of cycles N. ε^^-₂=Cσ^^-₂Δε^^-₁N^α, C, α ; material constants. The ratcheting behaviors were examined also when the strain amplitude was varied stepwisely or gradually with increasing number of cycles. For the description of ratcheting strain accumulation in this case, a modified strain hardening rule was proposed.

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The strain accumulations are observed in the mechanical ratcheting in the direction of the stress component superposed upon cyclic stress. To clarify the effects of variations of 'superposed stress' and of strain amplitude on the behavior of strain accumulations, the ratcheting tests were carried out using thin-walled tubular specimens of a carbon steel under the condition that both axial strain amplitude and internal pressure were varied stepwisely or gradually with number of cycles. A parameter ψ which represented the loading history was introduced. A parameter ψ which represented the loading history was introduced. A constitutive equation in the mechanical ratcheting under varied stress conditions was proposed by use of the parameter ψ on the hypothesis of linear superposition of 'superposed stress'.

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