Rotating bending fatigue tests were conducted on an austempered ductile iron (ADI) and a pearlitic iron (PDI) used for comparison purpose. Effects of specimen size, slicing location of specimen in casted block and material microstructure on the fatigue strength of both materials were examined. In addition, fatigue behavior was studied in each specimen through metallographic and fractographic observation. The fatigue strength of both materials were hardly influenced by the location of specimen collection, except the result of the material ADI at higher cyclic stress amplitude. Furthermore, both the materials indicated no size effect relevant to the fatigue strength. Concerning the microscopic aspect of the fatigue behavior, a non-propagating crack initiated at an defect was observed on each specimen, except the large-sized specimen of the material ADI, when the stress amplitude of the fatigue limit was repeated. In the fatigue range of stress cycles over 10⁷, a defect as small as the size of the spheroidal graphite particle induced in some cases fatigue failure in both materials.

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In this paper, stresses around an interface crack in carbon-fiber-reinforced plastic composites are analyzed. It is assumed that the material properties of the carbon fiber obey anisotropy, while those of the plastics obey isotropy. Boundary conditions are reduced to four simultaneous integral equations. To solve the equations, the differences of the crack surface displacements are expanded in a series of functions which are zero outside of the crack. The unknown coefficients which are accompanied in that series are solved with the aid of the Schmidt method. Neither oscillating stress singularities nor material overlaps appear in this solution, and physically acceptable stress intensity factors are obtained.

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Crack growth characteristics of a triphase steel composed of martensite, ferrite and graphite were examined through successive observation and fractography. The graphite precipitated in the ferrite matrix and martensite lowers the crack growth resistance. This is explained by the coalescence of a main crack and microcracks initiated by graphites near the tip of the main crack.

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A simple and new method of detecting for crack initiation at a notched section of a moving machine element is proposed and applied to a specimen with a blind hole. In this experimental case, the fatigue crack tip opening and closing point can be measured using the relation between the following function h and cyclic stress σ:h=ε_y+λε_x, λ=Δε_y/Δε_x, where ε_y and ε_x are the strains measured in the vicinity of the edge of the hole in the center axis, and Δε_y and Δε_x are the ranges of ε_y and ε_x, respectively. Crack initiation at the hole edge can also be detected with the waveform of such a function h. Furthermore, until the crack reaches the hole bottom, the crack length can be evaluated with the range of the subtractive function related to h. The detective method proposed can be expected to be applicable to the monitoring of crack growth in many real cases.

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This paper deals with the thermal shock problem of a hollow circular cylinder with an edge crack, initially at uniform temperature, being suddenly cooled on the circular surfaces. It is asuumed that the thermal disturbance near the crack surface may be neglected in the analysis of the temperature field of the elastic solid with a crack, because thermal shock occurs rapidly. We analyzed the transient thermal stress problem of a hollow circular cylinder with a crack and determined the stress intensity factor at the crack tip. The nondimensional maximum transient stress intensity factor is expressed as a function of Biot's number and the nondimensional crack length. We then proposed a simplified formulation of the nondimensional maximum transient stress intensity factor as a function of Biot's number and the nondimensional crack length.

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In this paper a nonhomogeneous elastic medium containing a crack arbitrarily oriented with respect to the direction of property gradient is considered. The problem is solved under plane strain or generalized plane stress conditions. This is a highly simplified version of a class of physical problems that may arise in fracture mechanics studies of ceramic coatings, metal/ceramic composites and interfacial zones with continuously varying volume fractions or graded properties. The main results of the paper are the calculated modes I and II stress intensity factors. Among the questions studied are the effects of the material nonhomogeneity constant, the crack orientation, the loading conditions, and the Poisson's ratio on the stress intensity factors. Briefly discussed are also the stress state near the crack tip and the crack opening displacement.

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An austenitic steel with high ductility, SUS 310 S, was found to show remarkable notch strengthening in circumferential V-notched specimens in a 700°C creep rupture test, resulting in maximum strength at the stress concentration factor of 2∼4. In notched specimens having a notch root radius as small as 0.05 mm, creep fracture occurred as a result of initiation and propagation processes of a main intergranular crack from notch root. But with increasing notch root radius, fine intergranular cracks formed throughout an area ahead of the main crack were found to be involved in a fracture process in addition to the one mentioned above. Finally, discussions were made on the notch strengthening of this steel and two conditions associated with creep stress and structural aspects of the material tested were proposed as responsibie for notch strengthening.

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The effect of hardener on the tensile fracture behavior of carbon fiber-reinforced plastic, CFRP, in which the pitch-type carbon fiber was combined in an epoxy resin matrix with a fiber content of 50 % by weight, was investigated using smooth and notched tensile specimens in a temperature range from 208 K to 413 K. The hardeners used were an acid anhydride and an amine line. Experimental results were discussed in terms of linear notch mechanics. The tensile strength and the fracture morphology of center-notched CFRP plates strongly depend on the test temperature. The brittleductile transition temperature is slightly affected by the notch tip radius, ρ, regardless of hardeners. In the case of the brittle fracture mode, the CFRP fails under the constant critical elastic maximum stress, σ_{max c}, which is determined by ρ alone. In the case of the ductile fracture mode, the fracture occurs under the condition of constant nominal stress in the net section which is independent of ρ.σ_{max c} was lower by about 15 % for an acid anhydride hardener than for an amine line. Furthermore, the transition temperature was lower by about 37 K for the former than for the latter.

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A theoretical relation is formulated by which the impulsive force generated at a contact part can be estimated, when an aluminum bar whose end is a truncated cone collides axially, perpendicularly against a plane wall at a comparatively low speed. In the formulation, the effect of the stress wave propagation is taken account. By comparing experimental results in which aluminum bars whose ends are of a variety of shape of truncated cones, collided against a devised sensing plate, with calculated results, the effectiveness of the theoretical relation for estimating the impulsive force which varies complexly with the shape of the contact end, impact velocity and length of the bar is confirmed.

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The dependence of acoustoelastic constants on external magnetic fields was experimentally investigated for JIS-SS41 steel specimens. In the case of ferromagnetic materials, the elastic wave velocities at a demagnetized state are slightly smaller than purely elastic velocities pertaining to a highly magnetized state. This occurs due to magnetoelastic interaction, which in turn depends on the stress state. In the present study, We measured the propagation velocities of longitudinal and shear waves in steel specimens as functions of uniaxial stress and external magnetic field. We found that in the demagnetized state, the velocity change with stress showed different slopes for compression and tension. This difference decreased as the specimens were magnetized, approaching its saturation. As for acoustoelastic birefringence, which measures the principal stress difference, the effect of magnetoelastic interactions is relatively weak, while for the longitudinal/shear wave velocity ratio, which is proportional to the sum of principal stresses, this effect may induce considerable errors. Magnetization of steel components can therefore improve the accuracy of acoustoelastic stress measurements. A discussion is given for the strength of magnetization required.

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One-dimensional, generalized thermoelasticity is presented based on Lord and Shulman's theory and Green and Lindsay's theory. The former theory involves one relaxation time of the thermoelastic process, and the latter involves two relaxation times. These theories have been developed in an attempt to eliminate the paradox of an infinite velocity of thermoelastic propagation inherent in the classical theory. A formulation of generalized thermoelasticity which combines both theories is derived. The generalized thermoelastic problems for a half-space are analyzed by means of Laplace transform technique. An approximate analysis for short periods of time is carried out because the effects of relaxation times are short-lived. The numerical results of the effect of the relaxation time on temperature and stress distributions are shown. And we point out the mistakes of the previous papers by Dhaliwal et al.

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As one of the analytical models of the thermal stress problem for composite materials, we consider an infinite plate composed of multilayered composite laminate and discuss the transient thermal stress problems of a laminated plate due to moving heat source from the upper surface. In order to develop the analysis for a multilayered composite plate, we introduce the methods of Fourier cosine and Laplace transform for the temperature field and Airy's stress function method for the thermoelastic field, and then evaluate the temperature and thermal stress distributions in a transient state. Extending the theoretical developments proposed in the present paper to the analysis of an infinite plate with nonhomogeneous material properties, we examine the thermal stress distributions and the effect of relaxation of stress values in nonhomogeneous plate made of functionally gradient materials.

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Analytical solutions are presented for a transient heat conduction problem and an associated plane thermoelastic problem expressed in elliptical coordinates in a confocal hollow elliptical plate subjected to nonaxisymmetric heatings on the inner and outer elliptical boundaries. The transient heat conduction problem is confined to a symmetric one with respect to the x axis, and solved by proposing new integral transforms and their inverse transforms, the kernels of which are expressed in the form of Mathieu and modified Mathieu functions. The associated plane thermoelastic problem is formulated in terms of Airy's stress function. The formulation includes an assurance of single-valuedness of the rotation component based on Michell's condition in elliptical coordinates derived already by one of the present authors. The numerical calculations of the distributions of the transient temperature and circumferential thermal stress are carried out for three cases of partial heating on the outer elliptical boundary.

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Combined tension-torsion creep tests of a Ni-base directionally solidified alloy are performed at 850°C using thin-walled tubular specimens solidified directionally in the axial direction. It is observed that equivalent creep rate depends markedly on the ratio of shear stress to tensile stress under constant equivalent stress of the Mises-type, while noncoaxiality between stress and creep rape is relatively small. Minimum creep rates obtained in the experiments are examined in comparison with related analyses based on the crystallographic slip theory. It is shown that the minimum creep rates are simulated well if the {111}<112> octahedral system is combined with the {100}<110> cubic system. The former is active in tensile creep of the specimen, while the latter is in shear creep.

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Deterioration of materials due to the formation of internal microscopic cavities induces the reduction of elastic stiffness. This stiffness reduction may have significant effects on the local distribution of stress, and hence on global results of inelastic stress analysis. The present paper is concerned with the formulation of the stiffness change induced by anisotropic damage on the basis of continuum damage mechanics, together with the experimental verification of the proposed theory. After discussing damage variables and effective stresses, the change of elastic properties in damage process is formulated by the strain equivalence hypothesis and effective stress determined by the present authors. The proposed theory is compared with those based on the hypothesis of strain energy equivalence, with M. Kachanov's theory, and with the corresponding results of creep damage tests on copper tubular specimens at 250°C.

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In this paper, the flow curve (the constitutive relation between shear stress and rate of shear) of a non-Newtonian fluid (liquid) is investigated on the basis of the first author's inelastic deformation theory. The theory is the combined deformation mechanism model and was proposed to explain the inelastic behavior of solids in the previous paper. The application of the theory to the flow curves of Newtonian, pseudoplastic, Bingham, plastic, and dilatant fluids leads to the possibility of the systematic explanation for these flow curves. The effect of temperature on the flow curve is also well explained. The theoretical considerations of the measurement values obtained by various researchers lead to the establishment of a maximum limit of rate of shear, which is assumed in the proposed constitutive equation.

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A simple numerical technique for solving inverse problems of two-or three-dimensional elasticity has been developed. The charge simulation method was employed to model an elastostatic system. The Kalman filter was directly used for the parameter estimation algorithm. An identification procedure of Young's modulus and Poisson's ratio was demonstrated using such example problems as elastic deformation of a hole in an infinite plane and compressive deformation of an elastic solid cylinder. A further study of the inverse technique using the charge simulation method included a stochastic system of which Young's modulus was not determinastic but stochastic. Fuzzy Young's modulus was defined to identify such a stochastic parameter. The fuzzy parameters of fuzzy Young's modulus can be determined by the probabilistic linear regression. A measuring system for elastic parameters of plant materials was exampled as an application of this inverse technique developed for parameter estimation problems.

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The stresses of band adhesive butt joints subjected to external bending moments, in which adhesive bonds were used partially at the interface, were analyzed using a two-dimensional theory of elasticity in order to establish the fracture criteria of joints. Similar adherends and adhesive bonds which were used at two or three regions at the interface were replaced with finite strips in the analysis. In numerical computations, the effects of the ratio of Young's modulus of adherends to that of adhesives, the thickness of the adhesive and the bonding area and positions on the stress distributions at the interface were shown. It was found that band adhesive joints were effective when the bonding area and positions were varied with external load distributions. The stress distribution near the singular point at the interface were expressed approximately. Photoelastic experiments and experiments concerning the strains of adherends were performed. The analytical results were fairly consistent with the experimental results.

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This paper deals with a two-dimensional stress analysis of butt adhesive joints with rigid fillers in an adhesive subjected to tensile loads. Assuming that adherends are rigid and replacing an adhesive with a finite strip including rigid fillers, the analysis was done using the two-dimensional theory of elasticity in order to examine the strength of joints. The effects of the location and size of rigid fillers on the stress distributions around the fillers and at the interface were shown by numerical calculation. For verification, photoelastic experiments were performed. The analytical result was in fairly good agreement with the experimental result. It was seen that by an amount of shift of location and size of fillers, the strength of joints was more improved than that of the joints without a filler. Discussion is also presented on the stress singularity at the edge of the interface.

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Central bursting is dealt with, with respect to the collapse of a unique solution. In general, there are two cases bringing about multiplicity : one is statical and the other is kinematical one. The latter corresponds to localized necking. These two multiplicities occur simultaneously in plane strain processes. There are two modes which can be realized at localized necking, but only one mode is possible in a plane strain process. The criterion for central bursting is given as(ε₁/n)(P/k)=-1, where P=average pressure, k=shear strength, ε₁ is the tensile strain in forming direction, and n is work hardening exponent. The influences of die geometry and manufacturing conditions on the central bursting are examined.

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Optimum cross sections of cylindrically coiled spring are analyzed by the growth-strain method. This method was previously proposed as a shape optimization method which deforms shapes by generating bulk strain. In the present analyses, the helix angle is neglected. The stress distributions are analyzed by the finite element method based on the stress function. The growth deformation is analyzed by the finite element method on the assumption of a roll of coil as a rotationally symmetric ring under free restriction. The bulk strain is generated based on the strain energy density in a manner in which volume change in the cross section is absorbed in the circuit direction. In consequence, a convergent curve of mass improvement ratio and corresponding cross sections are obtained. The cross sections are egg-shaped tapering to the outside of the coil.

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In this paper, the defect with noncircular shape in a two-dimensional structural component is identified by using the complex method incorporated into the two-dimensional elastic boundary element method. The method for searching for the defect is that the norm of boundary displacement, defined as the sum of the square of the difference between experimental values and numerical solutions, becomes minimum when the assumed defect coincides with the real one. The complex method is used to find the defect shape and position with minimal norm by iteratingly modifying the fictitious defect boundary within some constraint conditions without calculating derivatives. The procedure of defect identification is discussed under several numerical examples, and it is shown that the present method is efficient and accurate in searching for the real defect.

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Ceramics are typically brittle materials. However, fracture toughness of ceramics is variable with flaw size and also notch root radius. Generally, a process zone is formed ahead of the crack or notch tip. Numerous microcracks or phase transformations are formed in the process zone. The following are the main results obtained in this paper. Formation stress of process zone is equal to fracture stress or static fatigue limit stress of plain specimen. A new failure criterion based on process zone size is proposed. Based on the process zone size failure criterion, calculated failure stress as a function of crack size or notch root radius shows a very good agreement with experimented failure stress. Calculated process zone size is about 5 times the average grain diameter.

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Multiple objectives in the design of machine structures exist. Here, two types of priorities among these objectives are considered. One of these objectives is the absolutely necessary goal, the "required goal", and the other is the "requested goal". Few studies have been conducted with respect to the structural design problem of multiple goals with these kinds of priorities. Thus, a multilevel structural optimization strategy which is based on the lexicographic optimization method and modified so as to be available for structural design, is proposed in this paper. This strategy is demonstrated on an actual example of a motorcycle frame structural design which has three goals ; achievement of static torsional rigidity, reduction of dynamic response level and decrease in the weight of the motorcycle frame.

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