A better understanding of the debond and pull-out processes of fibers in fiber-reinforced composites is needed because they affect the fracture toughness of the composites. In this paper, a new stochastic model is proposed to predict the probability distributions of debond and pull-out lengths of fibers in a short-fiber-reinforced SMC composite. By considering that fibers in a short-fiber-reinforced SMC composite are discontinuous and that their dircection is random, the probability distributions of debond and pull-out lengths are predicted. It is found that the debond length becomes shorter and the pull-out length becomes longer than those in unidirectional continuous-fiber-reinforced composites. Furthermore, the influences of the fiber-matrix interfacial condition on the debond and pull-out lengths are clarified.

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A simple analytical method based on Hill & Hutchinson's formulations is proposed to determine the bifurcation behaviors which correspond to interfacial or surface instabilities of a laminated material. The characteristic equation which determines the bifurcation strain and its mode is derived from the general solutions of the basic equations and the mechanical and geometrical continuity conditions on the interface. The J2-flow and J2-deformation theories are used to formulate the constitutive properties and the power law is adopted to represent the uniaxial tensile stress and strain relation. The bifurcation analyses are performed on the laminated material subjected to the unidirectional tension. The present solution is proved to be reduced to the known solutions as certain special cases and is shown to be good agreement with numerical results obtained by the finite element method. It is concluded that when the skin material is harder than the core one, the possibility of the interfacial instability is predicted.

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Fatigue tests of HIP'ed SMF3035 were conducted on specimens with a circumferential groove whose diameters were different. As a result, it is successfully confirmed that linear notch mechanics (LNM) is available for the examination of notch effects in the fatigue of HIP'ed SMF3035. The master curves useful for the estimation of notch effects in HIP'ed SMF3035 were also produced by arranging the experimental data, based on the LNM. The main results obtained are as follows : Estimation of σ_W1, σ_W2 of HIP'ed SMF3035 with arbitrary shape is performed well by the LNM by using the master curve of K_tσ_W1, K_tσ_W2 vs. 1/ρ. There is some relationship between the notch radius of the branch point ρ_O and the static stress-strain curve. The notch radius of the branch point ρ_O is almost 0.5 mm, which is larger than that of steel having the same carbon content, and this may be caused by the different features of the pearlite structure in these two materials.

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Ti-6 Al-4 V alloy annealed at 760°C was low-cycle fatigued, and then strain-based fatigue life and the elastic-plastic fatigue crack growth were investigated. The Ti-6 Al-4 V alloy exhibited a significantly shorter crack initiation-and final failure-lives than did structural carbon and alloy steels when they were plotted against the plastic strain range, Δε_p. Meanwhile, the total strain-final failure life curves were situated on the short-life side in the high-strain regime and on the long-life side in the low-strain regime, respectively, compared with those of structural steels. There existed little difference in the crack growth rate, da/dN, plotted against cyclic J integral range, ΔJ, among Ti-6 Al-4 V alloy and structural carbon and alloy steels. The life spent for crack propagation, N_p, was successfully calculated by combining the da/dN-ΔJ relationship and the cyclic stress-strain response; the inflection behavior appearing in the log Δε_p-log N_p relationship was also satisfactorily assessed by the present calculations. Furthermore, the final failure life derived by using the crack initiation to final failure life ratio of N_i/N_f=0.20 was in good agreement with the test data.

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The statistical properties of the distribution of crack propagation fatigue life are of-ten needed for structural reliability analysis. Generally, many crack propagation tests are required to reliably obtain the statistical properties. However, the statistical characteristics can be obtained with far fewer crack propagation tests if the variability of the crack propagation fatigue life is mainly due to random crack propagation resistance. In this paper, the authors propose a simplified method for evaluating the standard deviation of crack propagation fatigue life using the results of constant ΔK tests. This method requires only the basic concepts of statistics and is applicable to reliability analysis even if there is no information on the distribution function of the random propagation resistance of the material. Using a random propagation resistance model, a Monte-Carlo simulation was performed to confirm the proposed method and satisfactory results were obtained.

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Corrosion fatigue behaviors of carbon steel specimens having different diameters were investigated experimentally in a sodium chloride aqueous solution. Based on these experimental observations Monte Carlo simulations of the corrosion fatigue process of different-sized specimens were conducted. The results of the simulations showed a good agreement with the experimental results. At a constant fatigue life ratio N/N_f, there was no specimen size dependence in the distribution of nondimensional crack lengths F(2l/d) and, at constant stress cycles, the distribution of crack lengths F(2l) is nearly constant regardless of the variations of the specimen diameters. Based on the above results, the simple estimation method of corrosion fatigue lives for the different-sized specimens was proposed. The estimated results give a good agreement with the experimental results.

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In order to investigate the effect of mean stress on fretting fatigue strength at elevated temperature, high-temperature fretting fatigue tests with various levels of mean stress were carried out using 12Cr-Mo-W-V steam turbine steel. The main results obtained are as follows. The fatigue strengths were decreased by fretting by a factor of three at both room and elevated temperatures regardless of the mean stress level. The modified Goodman relation held for fretting fatigue as well as for plain fatigue. The relationships between relative slip amplitude, friction coefficient and stress amplitude were independent of the mean stress level. The proposed method of fatigue life prediction based on fracture mechanics analysis, where the crack closure behavior was taken into consideration, was successfully applied to fretting fatigue with various levels of mean stress at elevated temperature.

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The effect of gas nitriding on fatigue behaviour has been studied on pure titanium under rotating bending. Smooth specimens were nitrided for 9 h at 850°C and 1000°C in pure nitrogen gas. The depths of the nitrided layer obtained were approximately 20μm and 55μm, respectively. The fatigue strengths of nitrided specimens were superior to those of untreated specimens ; in particular, fatigue strength was markedly increased by nitriding at 850°C, which was higher than that of specimens annealed at 700°C. Based on detailed observations of crack initiation, growth and fracture surfaces, it is concluded that the excellent fatigue strength of nitrided specimens is attributed to both improved crack initiation resistance and growth resistance by nitriding.

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In this study, the location, the angle and the size of a two-dimensional crack and the loading stresses are calculated by the data of strains measured around the region of the crack. Based on the consideration of the body force method that the strain field due to a crack can be represented by embedded force doublets, the problem is reduced to determining the location where the force doublets have to be embedded. In searching for the most appropriate place for embedding force doublets, that is, in searching for the location of a crack, the method of gradient search is used. By this method, the location of a crack is determined efficiently with good accuracy.

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This paper describes an expansion of statically indeterminate fracture mechanics to an elasticplastic fracture mechanics analysis. It can make it possible to evaluate tension and bending loads for a multi-edge cracked member of any structure subjected to combined tension and bending under displacement controlled conditions. Accordingly, the J-integral value can be evaluated from the tension and bending loads.

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It was shown previously that the CED (crack energy density) or its additional rate evaluated through the experiments of stable crack growth can be a parameter which expresses the fracture resistance, peculiar to fracture mode, of a material from the onset of stable crack growth to the rapid unstable fracture consistently. In this paper, simulation methods for stable crack growth by finite element analyses of the discontinuous model are studied, and the availability of CED above is confirmed through generation phase crack growth simulations corresponding to the experiments. The variation of the J-integral is also evaluated in simulations, and it is shown that the CED is more promising and reasonable than any J-based parameter to express the fracture resistance of a crack.

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In this paper, the J-value of an axially cracked cylinder under thermal shock, internal pressure and several pressurized thermal shock (PTS) conditions are evaluated over the full range of crack depth ratio (ζ) using a simple estimation scheme based on the deformation theory of plasticity which we proposed in our earlier works. Several parameter studies show characteristic features of the fracture strength under PTS as follows, The effect of internal pressure is predominant upon the J-value and dJ/da under PTS. Under any PTS condition, J-ζ relation shows that the J-value reaches its maximum at a certain ζ, then drops to zero (i.e., the starting point of crack closure) at ζ&sirne;0.9. The compliance of the cylindrical shell plays an important role in the fracture prediction of a pressure vessel. Under typical PTS conditions, the region at the crack tip dominated by the Hutchinson-Rice-Rosengren singularity is substantially large enough to apply the J-based criterion to predict unstable ductile fracture.

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Fracture toughness of sintered silicon nitride under mode I and mode II was studied at 800°C using controlled surface flaw in four point bending. Fracture paths in all cases were noncoplaner. The results were compared with various linear elastic fracture mechanics theories. The comparison showed that prediction by coplaner strain energy release rate theory, minimum strain energy density theory, and an empirical equation by Sigh and Shetty gave good agreement with the experimental values of this study. Normalized mixed-mode fracture toughness obtained at 800°C were comparable to those obtained at room temperature. Moreover, the grain shearing on the fracture surface which fractured in mixed-mode loading was found by fractographic study. The influence of grain shearing to crack propagation direction was discussed based on the fractographic observations.

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The effects of test temperature on fracture toughness K_C and on the fracture surface of columnar grained ice specimens were investigated at -5, -10, -30°C and -50°C. Sharply edge-notched specimens with section sizes of 25×50mm and 200×50mm were used. Three-point bending tests were conducted under the wide range of loaing rate K^^._I covering from 0.8 up to 3500 kPa√(m)/s. The pop-in crack propagation was also investigated at -10°C using 25×50mm specimens under K^^._I≒0.8 kPa√(m)/s. The K_C value and its scatter obtained under K^^._I≥30 KPa√(m)/s were substantially unaffected by test temperature and K^^._I. In K^^._I<30 kPa√(m)/s, the effect of test temperature on the K_C value was observed. The macroscopic fracture surface was affected by test temperature and K^^._I. Two types of pop-in cracks which extended along the grain boundary or the plane of cleavage were observed.

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Green's functions are shown for axisymmetric torsional body force problems of a dissimilar elastic thick plate. Green's functions are defined as solutions to the problem of a dissimilar elastic thick plate subjected to a torsional body force acting on a circle in the interior of the thick plate. As a special case for the Green's functions shown, we can obtain Green's functions for torsional body force problems of an elastic half-space, an elastic thick plate, a dissimilar elastic solid, an elastic layer on an elastic half-space, among others. A general method of solution is presented for torsional body force problems of a dissimilar elastic thick plate. The Green's functions shown here are obtained by applying the general method of solution. As an example of the application of Green's functions, we consider the torsion of a hemispherical rigid body embedded in the dissimilar thick plate. Numerical results for the problem are shown.

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In this paper, we deal with one of the methods to obtain a set of the free-space Green's function (fundamental solution) with respect to displacement components of a transversely isotropic infinite elastic medium which is subjected to a ringlike axisymmetric load. We assume that the load is tortionless. The solutions consist of the displacement components of the infinite elastic medium subjected to the load of radial and axial directtions. To solve the problem, we introduce two potential functions and apply the Hankel and the complex Fourier transforms.

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In this paper, we deal with one of the methods to obtain a set of the free-space Green's function (fundamental solution) with respect to strain and stress components of a transversely isotropic infinite elastic medium which is subjected to a ringlike axisymmetric load. We assume that the load is tortionless. The solutions consist of the strain and the stress components of the infinite elastic medium subjected to the load of radial and axial directions, respectively.

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In this paper, many numerical results obtained using a general-purpose program based on the body force method are presented. This program does not include any kind of numerical integrals and therefore makes it easy to obtain high-accuracy solutions of many kinds of two-dimensional elastic problems. In addition to the numerical results, the possibility of applying this prgram to engineering design problems is also discussed.

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In this study, the influence of Poisson's ratio in the elastic-plastic problems is discussed based on the body force method, in which the stress fields caused by plastic strain are replaced by the stress fields due to force doublets. It is shown that the elastic-plastic stress fields are independent of the Poisson's ratio under plane stress state, if the resultant forces of forces acting on boundaries and the body force acting in region are zero and if the rate of strain hardening H'/E is independent of Poisson's ratio.

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Two-dimensional torsional waves in an elastic/viscoplastic circular cylinder were analyzed numerically when torsional impacts were applied to the end face of the circular cylinder. For numerical analysis, the finite difference method based on integration along the bicharacteristics was employed. By obtaining the numerical results, it is demonstrated that, by this method, the propagation of two-dimensional torsional waves with time in the elastic/viscoplastic circular cylinder can be shown in detail. It is also found that this method is suitable for investigating the region of viscoplastic deformation in the circular cylinder.

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Theoretical modeling of acoustoelastic effects in plastically deformed solids has been accomplished through the use of an elastoplastic coupling strain rate. This coupling strain rate, which remains effective even under subsequent elastic loading, is considered to be generated at the yieldsurface vertex and causes elastic modulus degradation due to the growth of plastic anisotropy. The purpose of the present paper is to formulate precisely a generalized acoustoelastic theory for plastically deformed solids with finite deformation, and moreover, to provide the method of nondestructive evaluation of the plastically deformed state, i. e., yield surface, texture change due to the plastic deformation and the occurrence of the instability associated with the microslip band.

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For large deformation problems the well-known Green-Zerna theory is widely applied for elastic analysis. However, since this theory is independent of a strain history, the velocity strain (also known as the rate of deformation tensor) is mainly used for large plastic deformation in recent studies. In general, the rotation of the principal axis contains a rotation in space but also a change of the principal fiber element. Therefore, since the expressions of this strain are not associated with a fiber element, the velocity strain cannot discriminate the rigid rotation, which is the rotation of the principal fiber element, from the rotation of a fiber element. In this paper the expressions of the natural strain associated with a certain fiber element, which is elongated and rotated by deformation, are mentioned. The natural strain expressing the distortion of a fiber element is effective for large deformations on which an anisotropy brought about deformation is embedded in fiber elements.

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A new yield criterion and constitutive equations are proposed for the ceramic granule compact. Compressible behavior and dilatancy phenomena of the ceramic granule compact can be expressed by these basic equations. Experimental methods are also proposed to determine material constants which are necessary for the above-mentioned equations. These material constants of Al₂O₃ granule compact are actually obtained by the uniaxial compression test and compression test under uniform hydraulic pressure.

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In this paper, the particular behavior of the stress and the displacement fields near a corner of jointed dissimilar materials is studied as a plane problem. It is found that the order of the stress singularity is dependent on the deformation mode. The dependence of the order of singularity was established for the case of mode I and the case of mode II. An equation of stress field at the close vicinity of the corner is presented, in which the stress field is expressed as a sum of the symmetric state with a stress singularity of 1/r^1-λ1 and the skew-symmetric state with a stress singularity of 1/r^1-λ2. From the equation presented, it is shown that the stress field around the point singularity is defined in terms of two constants K_{I, λ1} and K_{II, λ2} as in the case of crack problems.

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This paper presents the stress intensity factor analysis of axisymmetric crack problems. A stress analysis is performed with the combination of the boundary element method and the finite element method, and then the stress intensity factor is calculated by the virtual crack extension method. First, the stress intensity factor analysis of a circumferential crack in a cylindrical bar under tension is performed and the results are compared with reference solutions to check the applicability of the present method. Then the problems of a crack in an outer or inner wall of a pipe under tension are analyzed. Approximate equations of the stress intensity factor for both problems are proposed.

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An analytical solution is presented for a plane-strain thermoelastic problem expressed in elliptical coordinates in confocal hollow elliptical cylinders with couple-stresses subjected to nonaxisymmetric steady-state heating on the elliptical boundaries. The steady-state heat conduction problem is confined to a symmetric one with respect to the x and y axes. The associated plane-strain thermoelastic couple-stress problem is formulated in terms of Airy's stress function and Mindlin's couple-stress function. The formulation includes an assurance of the single-valuedness of the rotation component in the confocal hollow elliptical cylinders with couple-stresses by Michell's condition expressed in elliptical coordinates. In order to demonstrate the effects of couple-stresses upon the behaviour of thermal-stress concentration in the vicinity of an elliptical hole in the confocal hollow elliptical cylinder, numerical calculations of the distribution of thermal stresses are carried out for three cases of aspect ratios of the elliptical hole and Poisson's ratio, and various values of new material constant based on Mindlin's couple stress theory.

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In this paper, the tension problem of a cylinder with spheroidal cavity is analyzed by the use of the indirect fictitious-boundary integral method in the linear couple-stress theory. The stress concentration factors and the stress distributions on a net section are obtained for various values of parameters, such as the characteristic length l, the diameter of a cylinder and the flatness ratio of a cavity. The results of the infinite problem with a spherical cavity are comparerd with the others. From the results, it is shown that, with increasing l, the axial stress concentration factor decreases monotonously, however, the hoop stress concentration factor decreases in the case of large stress gradient but increases in the case of small one.

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The cyclic behavior of recovery stress under constant maximum strain in TiNi shape memory alloy is investigated experimentally. The influence of maximum strain and the heating temperature in the thermal cycle on cyclic characteristics of recovery stress is discussed. The main results are summarized as follows. Both stresses at high temperature and at low temperature decrease gradually with the number of cycles, but the recovery stress is almost constant. Recovery stress under the thermal cycle decreases with maximum strain. Both recovery stress and stress at high temperature increase with the heating temperature, but stress at low temperature is almost constant. The amount of decrease in stress at high temperature under the thermal cycle is less than that in yield stress of stress-induced martensitic transformation in the pseudoelastic region. The infiuence of a rate of temperature variation on cyclic characteristics of recovery stress is slight.

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Plastic strain distributions on the net section of circumferentially notched cylindrical specimens are obtained using the Vickers microhardness test and numerical calculation. Notched specimens were loaded up to 0.7 P_max (P_max : maximum tensile load), 0.8P_max, 0.9P_max, 0.95P_max, P_max, 0.98P_max beyond P_max and 0.95P_max beyond P_max. Strains at a point were calculated by making an assumed curve of radial displacement touch at that point to the real curve of radial displacement distribution obtained from the hardness number distribution. The distributions of the equivalent and axial plastic strains are concave at all load levels tested. The equivalent plastic strain is a little greater than the axial plastic strain. The magnitude of the equivalent and axial plastic strains at the notch root at P_max is about twice as large as the axial plastic strain at P_max of unnotched specimen.

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The strain spectrum of elastic plane waves is analyzed on the assumption that the elastic modulus and the density continuously change in the connection of two linear elastic materials. At first, a pair of differential equations is derived which governs the variation of the spectra of the strain and the velocity. Numerical results are given for the following three cases of the connection. That is, the connection of two differeat elastic materials, the connection of the same materials, and the layered connection of two elastic materials. It is found that the transmission coefficient of the power spectrum of the strain varies according to the width, the density and the elastic modulus of the connection, or the variation of the number and the width of the layers.

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A stiffener shape optimization problem of thin plate built-up structures under compression is treated numerically. The stiffened plate structures are discretized into the isoparametric finite shell elements, and the sequential quadratic programming (SQP) method with a design sensitivity of buckling stress calculated by the finite difference scheme is applied to determine the optimal stiffener shapes which maximize a minimum bucking stress to which the volume is subjected. The optimal shapes of a unidirectional stiffener and a cross stiffener under uniaxial compression are calculated by the iteration of the SQP. From the results, it is recognized that the optimal stiffener shapes of the thin plates are closely related to the buckling modes.

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This paper deals with the strength of joints combining adhesives with bolts. The stress distributions in the adhesives and the variation of the bolt axial force were analyzed using an axi-symmetric theory of elasticity when an external tensile load was applied to the combination joint, in which two pipe flanges or two circular flanges were joined by adhesives, were clamped by nuts and bolts with an initial clamping force after they were joined by the adhesives. In addition, a method to estimate the strength of combination joint is proposed. Experiments were performed. The analytical results are consistent with the experimental results concerning the variation of the bolt axial force and the strength of joints. It is seen that the strength of the combination joint is greater than that of the adhesive joints and it increases with a decrease of the bolt pitch diameter. Furthermore, it is seen that the sealing performance of the combination joint, where the adherends are pipe flanges, is improved.

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This paper is concerned with a method for measuring an impact load acting on a body of arbitrary shape. The impact load is determined from the strain response of the body by the deconvolution procedure which is performed in the frequency domain by using Laplace transformation. The transfer function is estimated from the result of the calibration experiment. The deconvolution is one of the ill-posed problems, and it is usually difficult to obtain a good result. In particular, high- frequency noise involved in the measured signal is often expanded to obscure the result. For this problem, we used five estimators of the transfer function and investigated which of them gives the most suitable transfer function for the deconvolution of experimental data. The efficiency of the method is demonstrated by applying it to the instrumentation of the Charpy impact testing machine.

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In this paper, bone remodeling systems are studied by using rabbit tibia as an experimental specimen. The rabbit tibia is drilled and subjected to a cyclic compression load. The remodeling phenomena at the part of the circular hole defect of the tibia are evaluated by X-ray photographs and histologic examination. The results are compared with he numerical strain distributions which are analized by using the three-dimensional finite-element method. From these considerations, one possible healing process of bone defects is proposed.

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A new mesh refinement approach on h-adaptation for FEM is discussed in this paper. Since there are some limitations in the r-method, especially for problems with rather complicated domains, h-refinement was supposed to be an alternative for such problems. An ordinary local remeshing approach in the h-method has a great difficulty in controlling the mesh size depending on the error measures. As a result, the number of elements is very easily increased, and the computational efficiency in FEM is decreased. The purpose of our global remeshing scheme reported in this paper is to solve these problems. Our approach can be summarized as follows: generate subdomain data based on error measure, input these data into the automatic mesh generator which supports the subdomain data structure, then get very smooth and controlled refined meshes. Its effects are evaluated with several examples on both stress concentration problem and conductive heat transfer problem.

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The dependency of grown grain density on cyclic stress and temperature was examined by computer image processing. The relation among the increasing rate of grown grain density, cyclic stress and the absolute temperature of atmosphere could be expressed by a rate process equation, and the stress measurement method using an increasing rate of grown grain density was developed. The effect of temperature fluctuation of atmosphere on the accuracy of measurement can be evaluated on the basis of the rate process equation.

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The mechanical reliability of flexible printed circuits, FPC was studied upon the basis of the conventional works on fatigue of structural materials. The lifetime of FPC, N_f was related to the maximum strain of copper Δε_cu as the straight relation of Δε_cu∝N_f^-0.36 in the log-log diagram. It was found by experiment that the lifetime of FPC could be varied by controlling the tensile properties of adhesives and the thickness of copper foil, Kapton of the base material and adhesives. The lifetime, N_f could be improved by thinning the copper foil and adhesive and inversely by thickening Kapton of the base material. Also, there was an optimum rigidity-coefficient of the adhesive for the lifetime, N_f of FPC. During the lifetime of FPC, the fatigue process observed on copper foil could be divided into three stages as follows : the crack intiation, the crack density increase, the crack opening. The NG life of FPC, that is the electric resistance rising up to 10 % of the original value, was corresponded to stage of, the crack initation.

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In this paper, an improved version of a transversely isotropic inelastic constitutive model for a blood vessel is proposed. First, it has been observed that a steep curve of the cyclic internal pressure-diameter relation exists in the range of high internal pressure. In this model, a logarithmic type of a strain energy density function replaces the exponential one in the elastic part of the model. Then, a single evolution equation replaces the set of two to prevent ratcheting in the inelastic part of the model, which simplifies the model and makes it easier to identify the material constants. Based on the results from numerical calculations for uniaxial cyclic loading, stress relaxation tests as well as stress analyses under the condition of constant axial stretch and cyclic pressurization, it can be shown that the improved model describes well the anisotropic inelastic mechanical behavior of blood vessels.

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Effects of the temperature-rate term in nonisothermal modeling of kinematic hardening are studied. Two alternative forms of a nonlinear kinematic hardening rule (i.e., multisurface and multicomponent forms) are discussed, together with a linear kinematic hardening rule. With material constants determined from isothermal tensile tests of 304 stainless steel, stress-strain relations under monotonic and cyclic thermomechanical loads are calculated to find the following: For the multisurface form of nonlinear kinematic hardening, intersection of surfaces may occur, if the temperature- rate term or the relative translation term is omitted. Neglect of the temperature-rate term may result in anomalous shift shifting of stress-strain hysteresis loops under thermomechanical cyclic loading, if the kinematic hardening rule employed includes a linear or nearly linear component.

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Low-temperature strength is investigated for polyethylene film used for the observation balloons. Tension tests using danbel-type specimens and crack growth tests using the edge-cracked specimens have been conducted in the temperature range from 20°C to -40°C. The stress-strain curves show little anisotropy, and the yield stress increases as temperature decreases. The maximum load of edge-cracked specimens with the same initial crack length also increases as temperature drops, while elongation at fracture decreases after taking its maximum at 0°C. The crack-tip opening angle at steady-state propagation is a constant independent of the initial crack length and is considered to be a material constant. This value decreases as temperature decreases, and the crack tip becomes sharp at low temperatures. The net section stress at steady-state propagation is also constant under the present experimental conditions. The relationship between the J-integral and crack extension exhibits two straight lines and the value of the J-integral increases as temperature decreases.

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