Effects of serrated grain boundaries on the initiation and growth of short fatigue cracks were investigated using austenitic 21-4N heat-resisting steel at 973K in air. Grain boundaries were serrated by the grain-boundary reaction (GBR) precipitates. Fatigue cracks were initiated at second-phase particles and on the grain boundaries on which GBR precipitates did not form. Therefore, the crack initiation life in the specimens with serrated grain boundaries was almost identical to that in the specimens with straight grain boundaries. However, the subsequent short crack growth was influenced considerably by serrated grain boundaries, and the crack growth rate decreased more in the specimens with serrated grain boundaries than in the specimens with straight grain boundaries. The fatigue cracks were largely deflected at the GBP nodules on the grain boundaries. The deflection of the fatigue cracks was one of the most important factors for improvement of the fatigue crack growth resistance when crack length was less than a few hundred m.

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Low-cycle fatigue properties and surface crack growth behavior were investigated under two-step intermittent over-straining (ISO) of various strain ratios λ on low-carbon steel S 15 C and austenitic stainless steel SUS 304 specimens. The results obtained were summarized as follows : (1) The plastic strain range Δε_p as a cyclic deformation property did not change after IOS for S15C, but theΔε_p decreased after IOS for SUS304 because of remarkable strain hardening. (2) A retardation phenomenon in surface crack growth at low values of λ after IOS and cycles to failure N_f were observed for both the S 15 C and the SUS 304 specimens. When the value of λ increased, the retardation effect decreased and crack growth curves for S 15 C were at the front or rear of the curve of a constant amplitude test, but for SUS 304, the N_f decreased more clearly than that of the constant amplitude test because of the remarkable acceleration phenomenon after ISO. (3) When we arranged the surface crack growth rate da/dN with J integral range J under the IOS condition, the data lay in the range of a factor of two for the da/dN-J relations of the constant amplitude tests, in spite of repeated retardation or acceleration of crack growth after IOS.

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Fretting fatigue tests at room and elevated temperatures were carried out using a Cr-Mo-V steam-turbine steel. The fretting reduced the fatigue strengths by a factor of two at an elevated temperature (773 K) as well as at room temperature. The friction coefficients between the specimen and the contact pads increased in proportion to the appropriate stress amplitude. No significant difference in this behavior of the friction coefficient was observed between room and elevated temperatures. Predictions of fretting fatigue lives were made on the basis of the cyclic J-integral analysis proposed in the previous paper, where the frictional force between the fretting pad and the specimen was taken into consideration. The predicted lives were in good agreement with the experimental results at room temperature. At the elevated temperature, the predicted lives were shorter than the experimental ones, as a resulted of crack closure due to significant exidation. The predicted lives at the elevated temperature, where the oxidation-induced crack closure was taken into consideration, were in good agreement with the experimental results.

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In order to investigate the effects of the distributed surface cracks on corrosion fatigue crack propagation period N_p, rotary bending fatigue tests were performed on aluminium alloy in a sodium chloride aqueous solution by using 12 specimens under constant experimental conditions. N_p for the specimen tested in the lower stress amplitude (52 MPa) showed a tendency to decrease with increasing crack density or sum total of crack lengths observed on the specimen surface during corrosion fatigue process. However, N_p for the specimen tested in the higher stress amplitude (90 MPa) did not depend on these parameters. In the lower stress amplitude, crack coalescence behaviour is a dominant factor influencing the experimental results, because the greater part of cracks initiated during the corrosion fatigue precess could not continue to propagate without crack coalescence.

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The statistical property of the fatigue behavior was investigated for the heat-treated 0.45 % C steel plain specimens. The emphasis is to investigate separately the statistical properties of the initiation and propagation of microcracks through the successive observations on the specimen surface due to the plastic replica method. Results show that the Weibull distribution of the mixed type is well fitted to the crack initiation life distribution. On the other hand, the microcrack propagation life distribution and the crack length distribution are expressed as two-and three-prameter Weibull distribution, respectively.

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This paper describes the low-cycle fatigue of a cast iron disk in a cyclic rotating test and a uniaxial zero-to-tension fatigue test. In order to correlate the data, cyclic-elastic-plastic FEM analysis was made and the stress/strain amplitude was obtained. The low-cycle fatigue strength was accurately estimated from the uniaxial test when we used the average tangential stress theory with a slight modification. The number of broken fragments and SEM observations were also discussed in connection with the stress dependency of the rotating disk.

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For strength design of ceramic parts, static, static fatigue and cyclic fatigue torsional tests were carried out at room temperature on smooth specimens and notched specimens of sintered Si₃N₄. (1) The cyclic fatigue strength (maximum principal stress) at stress ratio R=0 was lower than the static fatigue strength. This was due to the effect of cyclic stress. The cyclic fatigue strength at stress ratio R=-1 was lower than that at R=0. This difference was almost equal to the difference in strength calculated from the effective volume. In this case, the effective volume of R=-1 is twice as much as that of R=0. (2) In the case of a gentle notch, both static torsional strength and cyclic torsional strength increased unlike in the case of static plane bending and rotating bending respectively. This can be accounted for by the difference in the effective volume.

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The corrosion fatigue (CF) crack growth behavior of 3.5 % Ni-Cr-Mo-V steel for offshore structures, which was heat-treated to two strength levels (846 MPa, I 150 MPa), was investigated under simulated sea-wave loadings and sinusoidal waves of constant amplitude. The sea-wave loadings were obtained from field tests in a seawater environment. The tests were performed at a free corrosion and a cathodic potential of - I 050 mV vs. Ag/AgCl in synthetic seawater. The CF crack growth rates of the higher-strength-level steel were highly accelerated compared to those of the lower-strength steel under simulated sea-wave loadings as well as under constant amplitude sinusoidal waves. At the free corrosion potential, the CF crack growth rates under the simulated sea-wave loadings were lower than those of the constant amplitude waves. At the cathodic potential, the crack growth rates of both tests were almost the same. The difference in crack growth rate between the simulated sea-wave and the constant amplitude waves was explained in terms of their fractographic features. The growth rates of the simulated sea-wave were nearly equal to the rates of the field tests : the CF behavior in the seawater field environment could be analyzed from the data obtained through simulated sea-wave loading tests in the laboratory.

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Polar materials or oriented media are typical examples of generalized continua. These materials, to some extent, are composed of particles that behave like rigid bodies or deformable particles, unlike the geometrical points of the classical continuum theory. Extending these theories in this paper, higher stage innner structures are further introduced successively in the microstructure. This continuum model can be called "higher stage polar materials". The kinematics of the 2nd stage polar materials are studied as an example of the n-th stage polar materials, and 2nd stage strain measures are obtained in addition to the conventional 1st stage strain measures. Applying this model, cross-sectional distortions of thin-walled open cross-section members are analyzed. Constitutive equations and balance equations are obtained, which have the same form as the conventional formula. We can regard the concept of "bimoment" in the theory of thin-walled structures as the couple-stress of the 2nd stage polar materials.

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In linear fracture mechanics, stress intensity factors controlling the fracture behavior of materials are calculated from stress distributions acting on the crack surfaces by the aid of superposition even for remote applied stresses. These stress distributions, however, cannot be measured directly in a state of crack opening because of the stress relief, which is seen in tensile residual stress fields for instance. In this report, such stress distributions are assessed by measuring the opening displacements along a crack under tensile loading, using the equation that was derived based on the complex-valued formulas on the stress and displacement of a two-dimensional crack. The known analytical opening displacements for cracks whose surfaces are subjected to a given stress distribution are used for numerically checking the validity of the equation. It was found that this method was available to the estimation of the stress intensity factors of central-cracks as opened by axial tensile loading, using rectangular specimens.

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In this paper, the surface crack problem in a cylinder subjected to internal pressure is solved. The analysis is based on the body force method, but it is different from the usual body force method in the following point. That is, the body forces to be continuously distributed on the imaginary cylindrical boundaries are approximated by some discrete point forces acting on the outside of the imaginary boundaries. By using this method combined with the resultant force boundary conditions, solutions with high accuracy can be easily obtained.

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Analysis of an internal semi-elliptical surface crack in cylindrical pressure vessels is practically important in order to evaluate brittle fracture or fatigue strength of pressure vessels. Therefore some researchers have tried to obtain the stress intensity factors for this problem. However there is some difference between these data. In this paper, the accurate values of stress intensity factor for this problem are calculated by the body force method in order to check the accuracies of those data. The differences between the stress intensity factor for this problem and that for a semi-elliptical surface crack in a semi-infinite body or in a finite-thickness plate are discussed. The approximate expression for the stress intensity factor for an internal semi-elliptical surface crack in cylindrical pressure vessels is also given for convenience of practical uses.

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The problem of determining the transient stress distribution in an infinite orthotropic plate weakened by two coplanar Griffith cracks is considered. An internal pressure is applied suddenly to the surfaces of the cracks. Application of the Fourier and Laplace transforms reduces the problem to the solution of a pair of dual integral equations in the Laplace transform plane. To solve these equations, the crack surface displacement is expanded in a series of functions which are zero outside of the cracks. The unknown coefficients accompanying in that series are solved with the aid of the Schmidt method. The stress intensity factors defined in the Laplace transform plane are inverted numerically in the physical plane. Numerical calculations are carried out for Boron-Epoxy composite materials. ************************************

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This paper presents a new approach to the bending analysis of thin elastic rectangular plates by the integral equation method. The fundamental idea of thin approach is to use functions which a priori satisfy the boundary conditions of two opposite ends. Thus, the plate bending problem can be reduced to a one-dimensional problem. By applying the integral equation technique to this one-dimensional problem, the solution is determined just as for the case of a beam. The present approach is based on the same idea as that of the finite strip method, or the Kantrovich method, but the number of degrees of freedom in this method is less than that of the finite strip method. A number of examples including various boundary conditions are computed, whereby the usefulness of the method is demonstrated.

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Three dimensional anisotropic bodies are analysed by the boundary element method with the fundamental solution of Wilson and Cruse. The effects of the accuracy of the fundamental solution obtained by the numerical integration on the boundary element analysis are discussed. Some crack problems are calculated by the present boundary element method. and the stress intensity factors for the cracks are obtained with fairly good accuracy.

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The back stress and overstress are phenomenologically determined by investigating the stress strain response of Modified 9Cr-1Mo steel at 550°C. The overstress is almost constant, and this feature is independent of both the strain range and the accumulated inelastic strain. Based on the investigation of the back stress, cyclic softening behavior is assumed to be caused by the softening of the back stress. An unified constitutive equation is proposed, of which internal variables are able to be related to the back stress and the overstress determined by the experiment. Simulated results of the present constitutive equation are compared with the experiments, to examine its applicability to the inelastic deformation behavior of this material at 550°C.

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The constitutive relation between viscosity, temperature and hydrostatic pressure of liquid materials is investigated by the inelastic deformation theory (combined mechanism model) proposed in the previous paper in order to explain the inelastic behavior of solid materials. The constitutive relation of water and some other liquid materials is well-explained quantitatively by the theory. The following are obtained : liquid flow due to several mechanisms, which are the thermal activation processes similar to those of solid materials ; the liquid region in a pressure-temperature diagram is divided into several (mainly three) subregions classified by flow mechanism ; a proposed constitutive equation containing hydrostatic pressure.

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Two-dimensional stress waves in elastic/viscoplastic circular tubes were analyzed numerically, when axisymmetric impacts were applied to the end face of the tubes. For the numerical analysis, the finite difference method based on integration along bicharacteristics was employed. By obtaining the numerical results for the cases of various sizes of the tube, and of the impact loading condition, it was confirmed that when the rise time of the applied impact velocity is sufficiently short, and when a viscoplastic deformation takes place near the impact face, the maximum value of the caused tensile stress is much smaller than when only an elastic deformation takes place. Even when the viscoplastic deformation takes place, the possibility of the occurrence of the impact fracture in the cylinder containing a small-coaxial hole is much higher than the case of a cylinder with no hole.

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A boundary element technique based on the time-stepping formulae is proposed for the transient elastodynamic problems. The acceleration term of the basic differential equation of elastodynamics is approximated by finite difference on time, Newmark's single-step formula and Wilson's formula. This approximation enables boundary element formulation by using the same fundamental solution as that of the steady-state elastodynamic equation. The present paper deals only with the one-dimensional problem under an impact force to confirm the effectiveness of the method. The numerical examples reveal that the Wilson θ method is the most suitable scheme among the three to incorporate with the Boundary Element Method, and that the proposed method is promising for two- or three-dimensional problems and other complicated coupled problems.

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In this study, the body force method was extended to the analysis of elastodynamic problems. By inserting the region in question into the adjoint region, it was possible to reduce the given elastodynamic problem to an elastodynamic problem of an infinite body. The general integral formula was obtained based on superposition of the elastodynamic fields of a point force and a discrepancy in the time-space region. Therefore, analysis of the elastodynamic problem was reduced to a calculation of the unknown densities of force or discrepancy distributed along the imaginary boundary. The direct or indirect methods of BEM can be seen as special cases of the general formula proposed in this study. The effectiveness of the method was shown by analyzing an example of the elastodynamic problems of a half space with initial conditions subjected to uniform surface pressure.

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Crack Energy Density (CED) is a parameter which is clearly defined, without any restrictions on constitutive equations, throughout the life of a crack, and which is expected to describe, successfully and in a unified form, almost all kinds of behavior of a crack. Therefore, CED can be reasonably defined for a 3-dimensional crack as well, and its definition and the fundamental matters concerned have already been discussed. In this paper, 3-dimensional elastic and elastic-plastic finite element analyses of a center-cracked specimen under tension are carried out using a continuum notch model and discontinuous model (generalized Dugdale model), and the distributions of CED along the crack front line are evaluated by previously obtained path-independent expressions. The availability of path-independent expressions in the evaluation of CED is examined, and the applicability of the discontinuous model to 3-dimensional crack problems is shown through these results.

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Fracture phenomena and energy-absorbing capacity of a thin metal sheet under penetration by a 20.5 mm-diameter cylindro-conical projectile are studied experimentally. The top angle of the projectile is 45 degrees, and the diameter of the top spherical surface is 5.5 mm. The materials of the sheet used in this study are Extra Super Duralumin (7075-T6), Corrosion-resisting Aluminium Alloy (A 5083 P) and Cold Rolled Carbon Steel (SPCC), whose thickness and diameter are 1.0 mm and 200 mm, respectively. On SPCC and A 5083 P, the Energy-absorbing Capacity U_T is almost equal to the energy of crack extension and dynamic U_T is about twice that of the static one. However, on 7075-T 6, the energy of petal bending is half as much as U_T and dynamic U_T is equal to the static one.

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The source analysis of AE due to the crack extension in ceramics is described. The vertical force released by the pencil lead fracture has been used as the artificial AE source. The transfer function of input/output signals is determined experimentally. Analysis is first carried out to investigate the phenomena of dips induced prior to the arrival of the surface stress emission. The amplitude of the dip depends on the length of the lead, which suggests that the creation of the dip might be caused by the stress pulse from the lead. It is shown that the AE source wave, D, associated with the crack extension in graphite corresponds well to an energy release rate, G. Results in vitrified grinding wheels with different grain diameters reveal the tendency of the AE source waveforms to coincide with each other irrespective of microstructures.

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The previously proposed convenient J_IC test method using a Charpy-size specimen with side groove was successfully applied to various types of welded joints with heterogeneity in strength. The J_IC-value in the heat-affected zone could be determined by the convenient J_IC test method using a small Charpy-size specimen even when the CT specimen was too large in size to determine the J_IC-value in the heat-affected zone of an X-groove welded joint. The range of applicability of the convenient J_IC test method seems to be the range in which the obtained J_IC-value satisfies the condition of 25.4 mm>25 J_IC/σ_flow.

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It is well known that coarsening of carbides, intergranular impurity segregation and other microstructural change degrade the fracture toughness of ferritic low alloy steels after long service operation. The ductile-brittle transition temperature (DBTT) odtained by Charpy V-notch impact test and its shift after service operation is one of the most useful measures of the fracture characteristics of these materials. However, it is difficult to extract multiple specimens for CVN tests without damaging the components. In this study, the ductile-brittle fracture mode transition behavior of ferritic low alloy steels was investigated by means of a small punch test technique in relation to CVN DBTT behavior. The experimental results revealed a single linear correlation between the DBTT obtained from small punch test and that obtained from a Charpy V-notched impact test for various kinds of ferritic low alloy steels.

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An essay for the formulation of magnetoelastic interactions is pressented in polycrystalline ferromagnetic materials. The special attention is directed to the stress-strain characteristics in polycrystalline materials known as the ΔE effect. The new variable, the relative volume of magnetic domains in a crystallite with multi-domain structure, is introduced to explain the ΔE effect in demagnetized specimen, which could not be understood by the earlier theory of magnetoelastic interactions. It is shown that the stress induced magnetostriction is arised, and that the apparent elastic stiffness is reduced independently of the sign of magnetostriction constant. Specific examples of uniaxial stresses, shear stresses are examined to show the occurrence of the ΔE effects also in polycrytalline materials.

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Rice has proposed a simplified method for estimating the J-integral for a CCT specimen. Ohji has also suggested a simplified method of estimating the J-integral for the same specimen. These J estimation formulas have been derived based on the assumption of a deep crack. In this study, the applicable range of these J estimation formulas is analytically studied for four materials ; linear elastic, rigid perfectly-plastic, elastic perfectly-plastic and elastic-plastic. The necessity of a deep crack for these J estimation formulas is also studied analytically for a strain hardening plastic material for L/W>3 when a load-point displacement is used. Results show that these formulas are valid for any 2a/W for three materials ; linear elastic, rigid perfectly-plastic and elastic perfectly-plastic, and that the use of a mouth opening displacement is superior to the use of a load-point displacement in the applicable range. Results also show that a deep crack must be assumed for n≲3 when L/W=4. Based on the results, we can conclude that a mouth opening displacement should be used for estimating the J-integral for a CCT specimen.

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Based on the superposition technique, the effect of residual stress on the fatigue crack growth rate has been estimated to be the same as the effect of the applied stress ratio, considering the effect of the crack surface contact. In this paper, a simpler method to analyze the partial crack surface contact is proposed. The changes of the real stress intensity factor in a load cycle on a compact specimen with a welding residual stress field is analyzed numerically. The effect of a notch machined into the compact specimen is also analyzed. The results obtained are as follows; (1) The simpler method with the superposition technique can be applied. (2) Because of the crack surface contact, the real stress intensity factor range is reduced and the real stress ratio becomes is heigher than O in a compressive residual stress field. (3) The real stress intensity facor is kept constant from the onset of the crack surface contact to the complete unloading on the compact specimen. (4) The notch machined into the compact specimen reduces the effect of the partial crack surface contact.

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A new algorithm for the improvement of measuring accuracy of ultrasonic attenuation using a spectrum analysis has been developed. Normally, the ultrasonic attenuation is evaluated from 1st and 2nd peak values of the pulse-echo ultrasonic wave. However, the attenuation values evaluated by this method possibly contain some error, because those values are greatly affected by the superimposed noise. The proposed method removes this problem by evaluating the attenuation values from the expected envelope curve of the original ultrasonic wave. The algorithm developed is incorporated in, measuring system which consists of a personal computer with ultrasonic apparatus and a digital storage oscilloscope. Several ultrasonic waves obtained from Monte Carlo simulations and high-temperature fatigue-damaged specimens are analyzed by using both the proposed method and the normal method. It is concluded that the measuring accuracy of ultrasonic attenuation by the present method is higher than that by the normal method.

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The increase of temperature produced by the plastic deformation at the crack tip has been measured by a thermal video system (TVS). It has been found that the distribution of the temperature increase ΔT_p in the plastic zone is proportional to 1/r where r is the distance from the crack tip. The above result has been explained by the fact that the plastic strain energy at the crack tip, which is expressed by the HRR solution, has the singularity of 1/r. A method of measuring the J-integral by the TVS has been proposed and the subjects for the future inprovements have been discussed.

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The present paper is concerned with the development of a stress analysis program, named SIMUS 2D/F, which can analyze the stress state of thin multilayer structures such as LSI (Large Scale Integrated) devices through their manufacturing processes. This program has three special )features : (1) flexibility for the change of the modeling region in the deposition process of thin films, (2) efficient calculation by reduction of the modeling region assuming an equivalent wafer, (3) viscoelastic analysis with temperature-dependent material properties.

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The cyclic characteristics of the shape memory effect in Ti-Ni alloy helical springs are investigated in thermomechanical cycles. In the experiment, an offset-crank shape memory alloy heat engine is used. The results obtained show that : (1) Nonrecoverable elongation and recovery rate vary significantly in the early cycles, but show slight variations after these cycles. (2) Elongation based on reversible shape memory effect increases gradually with the number of cycles. (3)Axial force corresponding to the maximum deflection decreases slightly in the early cycles, but shows a constant value after these cycles. (4)When the maximum torsional strain on the surface of the helical spring becomes larger than 2%, the rate of increase in nonrecoverable strain becomes greater while that for axial force decreases. (5) The resting period does not affect shape memory characteristics. (6) The number of cycles to failure decreases linearly with the range of torsional strain on the surface of the helical spring.

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Experiments on Ti-Ni shape memory alloy wire under uniaxial tension with thermomechanical cycles were carried out. The influence of shape memory processing temperature and maximum strain upon cyclic characteristics of the shape memory effect were examined. The results obtained are summarized as follows. (1) Both recoverable strain with shape memory effect and strain range with stress-induced martensitic transformation show almost the constant values for thermomechanical cycles. (2) Residual strain increases in the early cycles, but shows a constant value after these cycles. (3) Two-way strain with reversible shape memory effect increases with the number of cycles. (4) Residual strain is proportional to two-way strain ; both strains are proportional to maximum strain. (5) Yield stress of stress-induced martensitic transformation decreases significantly in the early cycles, but decreases gradually after these cycles. The yield stress decreases for high shape memory processing temperature. (6) Stress corresponding to maximum strain decreases with the number of cycles, but the amount of the variation is small.

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The mechanical components of a ball thrust bearing, constant-velocity universal joint, locker arm of a cam driving a cylinder valve and a ball-type pressure-regulating valve, involve the elements of a sphere and an anvil. These are subjected to impact load. In this paper, we suppose a model with the simplest form of only a sphere and an anvil for these complex components. The sphere and anvil are in contact with each other and rest along the straight line joining their centers. When the free-side end of the anvil undergoes the normal collinear impact by travelling around the bar, the impact load transmitted into the sphere adjacent to the anvil is theoretically analyzed by a motion equation and Hertz's contact theory. It is important to find the particle velocity evoked by the arrival of a stress wave at the end of the anvil which is a point contact with the sphere. This particle speed is an initial velocity as the anvil transmits the load into the sphere. The validity of theoretical analysis is confirmed by comparison with an experiment under the same conditions.

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A numerical method is presented for investigating harmonic waves propagation in arbitrary anisotropic laminated strips. The laminated strip is divided into N elements (along the thickness). The displacement field within each element is approximated by a linear expansion in thickness direction and by series in width direction. The principle of virtual work is applied to establish the eigenvalue equations. As a example, the dispersion relations are determined for unidirectional carbon/epoxy laminated strip and hybrid composite laminated strip which consists of carbon/epoxy and glass/epoxy layers.

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A semiexact method is presented for investigating harmonic wave propagation in arbitrary anisotropic laminated bars of rectangular cross section. In the thickness direction, the laminated bar is divided into N plate elements. The displacement field within each element is approximated by a linear expansion in the thick direction and exponential functions in the other two directions. The principle of virtual work is applied to determining the characteristic values in the width direction. Then the dispersion relations are obtained by using boundary conditions. As examples, the characteristic frequencies are calculated for an isotropic bar, an unidirectional carbon/epoxy laminated one and a hybrid composite laminated one which consists of carbon/epoxy and glass/epoxy layers. The results of the isotropic bar and unidirectional carbon/epoxy laminated one are compared with those obtained by other methods.

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The wave propagation in arbitrary anisotropic laminates is investigated on the basis of an exact theory. The Lamb wave dispersion relations are determined for graphite/epoxy symmetric angle-ply laminates and hybrid composite ones which consists of carbon/epoxy and glass/epoxy layers. The energy distributions in the thickness direction of laminates are calculated for each kind of Lamb wave. The hybrid composite laminate is found to have a capability of impact energy absorption by analyzing the strain energy distribution during the wave propagation. This result is useful in determining the arrangement and the fiber orientation of the layers of hybrid composite laminate.

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