The influence of applied stress ratio on the fatigue strength of carbon steel coated with TiN was studied on the basis of the measurement of crack initiation by the DC potential method. Fatigue tests were performed under the stress ratios of R=0 and -1 in air by using the round notched specimens of 0.37% C steel normalized, JIS S35C, coated with TiN by PVD and CVD. From the experimental results, increase of fatigue strength was observed in TiN-coated specimens under the tests of R=-1, as compared with that of the uncoated specimen. However, the fatigue life of coated specimens by PVD was decreased under the tests of R=0, except for the region of low stress amplitude. Moreover, the fatigue life of specimens coated by CVD under R=0 was smaller than that of the uncoated one. The difference of fatigue life with applied stress ratio is explained by the fracture behavior of coating film on the specimen surface.

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In this paper, rotating-bending fatigue tests for polyetheretherketone (PEEK) were carried out to investigate the fatigue characteristics of plain and notched specimens at room temperature. The results were discussed using linear notch mechanics. In the case of the plain specimen, fracture always occurs from defects and the crack growth rate is very high. The fatigue crack initiation of this material is of the point-initiation type and the fatigue strength is very sensitive to a notch. The fatigue strength of an arbitrarily notched specimen of this material will be estimated from the present results rearranged based on linear notch mechanics.

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Axial strain-controlled fatigue tests and tensile peak strain hold fatigue tests were conducted on alloy 800H in 850°C∼950°C air to investigate the effect of the stress relaxation process on the fatigue life of the material. Subsequently, it was noted that the fatigue lives were only slightly affected by temperature in this high temperature region. It was also recognized that fatigue life decreased with the introduction of tensile strain hold time, but the effect of strain hold time on fatigue life saturated in a rather short strain hold period due to the rapid stress relaxation behavior of the material in these temperatures. These results were investigated from the viewpoint of microstructural changes and fractographic features of specimens. Finally, creep-fatigue damage interaction values were calculated and D=0.4 was found to be the optimum minimum damage value of this material.

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In this study the location of an edge crack emanated from a circular hole and the loading stress are calculated by the data of strains measured around the region of the crack. The location of the crack is determined by the gradient search. In order to avoid the trouble due to local minimum the starting point of searching process is selected based on the fact that the strain field due to crack can be represented by embedded force doublets.

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Analysis of an external semi-elliptical circumferential surface crack in hollow cylinders is practically important in order to evaluate the static or fatigue strength of pressure vessels or pipings. However there are few papers which treated this problem. In this paper, the accurate values of stress intensity factor for this problem are calculated by the body force method. The differences between the stress intensity factor for this problem and that for a semi-elliptical surface crack in a plate are discussed. According to these results, the stress intensity factors for a semi-elliptical surface crack in a hollow cylinder can be approximated by those for a semi-elliptical surface crack in a plate within about 3% in the case when t/<R_i>≤0.4, 0.5≤b/a≤1.0 and b/t≤0.6. The stress intensity factors for a semi-elliptical surface crack in a shaft were also calculated in order to check the accuracy of this method. Their approximate expressions, effective for practical application, are shown.

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The reopening behavior of longitudinal cracks which are induced by hydraulic fracturing on the surface of a borehole is analyzed to establish the methodology of hydraulic fracturing tectonic stress measurements. To this end, a model is constructed to analyze the coupled problem of fluid flow in the crack and the crack reopening behavior in impermeable rock, based on the linear theory of elasticity and also on the linear fracture mechanics and taking into account that the crack does not reclose perfectly upon deflation due to crack surface damage and some minor shear displacement. The results show that the borehole pressure at the instant when the crack reopening occurs is just half of the pressure value predicted by the conventional theory. The borehole pressure at which the pressure-time history apparently deviates from a linear behavior is somewhat higher than the true pressure value at the crack reopening, and it increases with water injection rate.

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A method of testing elastic-plastic fracture toughness under mixed-mode loading was proposed using a single-edge-cracked specimen subjected to bending moment and shearing force. The J-integral of a crack in the specimen is expressed in the form of J=J₁+J_II, where J_I and J_II are the components of mode I and mode II deformation, respectively. J_I and J_II can be estimated from the M-θ diagram (M : bending moment, θ : crack opening angle) and F-U diagram (F: shearing force, U : crack shearing displacement). In order to obtain the M-θ diagram and F-U diagram, a new deformation gauge for a mixed-mode crack was developed by using optical-position-sensing devices. The elastic-plastic fracture toughness tests under mixed-mode loading were carried out on aluminum alloy 6061-T651. The crack initiation from a mixed-mode crack occurs in the tensile type and shear type depending on the loading mode. As the mode I component becomes more predominant, the tensile type crack is initiated in a brittle manner. On the other hand, under a mode-II-predominant loading, the shear-type crack initiation occurs in a ductile manner. The condition of crack initiation from the mixed-mode I-II crack is shown by two curves for the tensile type and shear type on the J_I-J_II plane.

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This paper describes an experimental study on crack propagation properties of a single crystal Ni-base superalloy, CMSX-2, under creep-fatigue loading. The following points were made clear : (1) The crack propagation properties of CMSX-2 under creep-fatigue loading were approximately divided into two types, cyclic dependent, PP and PC waves, and time dependent, CP and CC waves, ones similar to those of polycrystalline metals. (2) The result is due to a difference of fracture modes, gamma prime transphase fracture in cyclic dependent crack propagation and gamma prime interphase fracture in time dependent crack propagation. (3) In time dependent crack propagation, the resistance to crack propagation under CP loading was smaller than that under CC loading because of a difference of creep in the process of compression, similar to that in polycrystalline austenitic stainless steel at a high temperature.

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In order to achieve the objective of securing the reliability of high-temperature components, it is necessary to establish a method for predicting the remaining life of their materials subjected to severe creep-fatigue damage. It was reported by the authors that multiple small cracks initiated along grain boundaries on the specimen surface at the very early stage of life in creep-fatigue and their growth and coalescence formed the main crack which induced the failure. Moreover, the process of small crack initiation and growth showed random behavior due to microstructural inhomogeneity. A stochastic model was proposed and the failure process was numerically simulated by means of the Monte Carlo method. This paper provides a scheme of the small-crack-simulation-method for the evaluation of remaining life of the materials in high-temperature components, which is an integration of our previous studies and is summarized in a flow chart.

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In this study, the mode I-II mixed-mode tests were carried out on thin-sheet center-cracked specimens of 2024-T3 Al-alloy using the mixed-mode testing method shown in Fig. 1(b), which was been proposed by the present authors in a previous paper. The condition for initiation of stable crack growth was investigated in terms of the J-integral. The results were compared with those obtained in the previous paper using slant center-cracked specimens of 2024-T3 Al-alloy, as shown in Fig. 1(a). The following conclusions were obtained. (1) When the proposed testing was applied, the stable crack initiation load was considerably lower than the plastic collapse load in every mode I-II mixed-mode region, whereas in the mixed-mode tests using slant center-cracked specimens, the stable crack initiation load was almost eqaul to the plastic collapse load in the region near the pure mode II condition. (2) When the proposed testing method was used, stable crack initiation was found to follow the relation J_I+ηJ_II=(J_i)_I in every mode I-II mixed-mode region, where J_I and J_II are the mode I and mode II components of the J-integral, (J_i)_I is the J-value at stable crack initiation under the pure mode I condition, and η is a constant. On the other hand, in the mixed-mode test using slant center-cracked specimens, the experimental results deviated from the relation J_I+ηJ_II=(J_i)_I in the region near the pure mode II condition.

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The present study aims to develop a rate-type evolutional equation for the anisotropic internal state which has been discussed in previous studies. The approach employed follows the general formalism of irreversible thermodynamics. We first define a free energy function and discuss the thermodynamic forces associated with the assumed internal variables on the basis of the Clausius-Duhem inequality. The evolutional equations of the state variables are described by means of a dissipation potential which includes recovery potential. The model has the feature of fictitious decomposition of the internal state variables and the associated dual variables into the isotropic and kinematic parts, respectively. An additional state variable is naturally introduced in the extension, which may describe an effect of nonproportionality.

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Stress intensity factors around an insulated crack situated parallel to the plane surfaces of an infinite elastic layer are determined. The upper surface of the layer is heated to maintain the constant temperature T₀, while the lower surface of it is cooled to maintain the constant temperature -T₀. The thermoelastic problem is reduced to that of solving a pair of dual integral equations. To solve these, the difference of the crack surface temperature and those of the crack surface displacements are expanded in a series of functions which are automatically zero outside of the crack. The unknown coefficients accompanied in the series are solved by the Schmidt method. The stress intensity factors and the strain energy release rate are calculated numerically.

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An analytical expression is presented for the thermal stresses in orthotropic nonhomogeneous infinite plates with arbitrary nonhomogeneities both in elastic properties and coefficient of linear thermal expansion, and temperature variation through the thickness of the plate. Numerical calculations showing the effect of the nonhomogeneous thermal and elastic properties on the relaxation of the thermal stresses increasing by the orthotropic properties, are carried out for the case of exponentially or linearly varing thermal conductivity, Young's modulus and coefficient of linear thermal expansion through the thickness of the plate. An application of the numerical rusults to the design of functionally gradient materials (FGM) is discussed.

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The fatigue limit of high-strength steel is influenced by inclusions and defects. Once a crack emanates from an inclusion or a defect, a fisheye (an embedded elliptical crack) is often formed. The stress intensity factor for a fisheye is important to evaluate the fatigue limit. In this paper, the stress intensity factors for an embedded elliptical crack in a long shaft under tension or bending are calculated by the body force method. The differences between the stress intensity factors for this problem and those for an embedded elliptical crack in an infinite body or in a semi-infinite body are discussed. According to these results, the stress intensity factors for an embedded circular crack in a long shaft under tension or bending can be approximated quite well by those for an embedded circular crack in an infinite body. The approximate expressions for the stress intensity factors are also shown.

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In order to clarify the effects of the fluid flow rate and stress amplitude on the the initiation and growth behavior of corrosion pits, round, smooth specimens were rotated with various speeds in sodium chloride aqueous solution. The results are summarized as follows : [1] The pit growth behaviors were prescribed by Eq. (1), regardless of fluid flow rates and stress amplitudes. [2] The pit initiation time decreases with increase of the fluid flow rate and stress amplitude. [3] For small pits whose sizes are about 0.03mm, the pit growth rates increase with the fluid flow rate, while the growth rates for pits above 0.08mm are independent of the fluid flow rate and smaller than those of 0.03mm. The pit growth rate in the case of 100MPa is 5∼10times lager than those of nonstressing.

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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 external bending moments. Assuming that adherends are rigid, and replacing an adhesive with a finite strip including rigid fillers, the analysis was performed 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 calculations. For verification, photoelastic experiments were performed. The analytical result was in fairly good agreement with the experimental result. It was seen that due to the amount of shift of location and size of fillers, the strength of joint was more improved than that of the joints without a filler. The stress singularity at the edge of the interface was discussed.

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A thick-walled ring for Al/SiC functionally gradient material (FGM) was manufactured by the method of centrifugal casting technique. The gradient distribution of SiC powder in the aluminum matrix was confirmed. The SiC powder-distribution profile correlated well with the variation of the vikers microhardness. Compression tests were performed at 300 K, 450 K, 630 K, and 780 K using conventional cylindrical specimens which had a gradient composition toward an alignment of the loading train. The deformation loads for FGM are greater than that for aluminium alloy of the matrix, and the influences of strain rates were observed. A plastic instability of flow softening or negative strain hardening was observed in a high-temperature compression test. Nonuniform barreling was also observed, and the effects of a flow stress gradient caused by the composition gradient were discussed.

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The estimations of residual deformations are considered for tanks subjected to extenal pressure that are composed of cylindrical panels and stiffened plates. For cylindrical panels the estimation of buckling strength is conducted by nonlinear finite element analyses taking geometrical imperfections into account. Also experiments are conducted. For stiffened plates the stiffness increases with the deformation. The large deformation beam theory with boundary stiffness can be used to estimate the plastic residual deformations.

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A two-dimennsional finite element analysis was perfomed to study a redistribution of residual stresses due to cutting in a ceramic/metal joint. The cutting process was simulated based on a tying function of the program where two kinds of nodes (one is the tied node and the other is a retained node) were defined at the same point on a cutting line. Release of restraint of these points means cutting. It is concluded that the residual stresses redistribute after cutting the ceramic/metal joint and the peak tensile stress occurs on the new free surface near the interface in a ceramic side. It is emphasized that the residual stress at a same point decreases after cutting, but the maximum value does not decrease.

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In the large deformation analysis, the utilized constitutive equation will play an important role on the finite element solutions. The present paper shows the numerical solutions for large elestic deformation using the constitutive equation with the Green derivative, which has not been studied in details in previous works. Three kinds of shear deformations of two dimentional block in plane strain conditions are taken as examples, and discussed are the effects of isoparametric shape functions and gaussian integration points on the finite element solutions.

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The stress field in a composite under plane deformation depends on only two combinations of elastic constants if there are no net forces on internal boundaries. In this study the above result is discussed based on the body force method, in which the stress field caused by inclusion is replaced by the stress field due to force doublets. The discussion is closely related with the fact that the stress field due to force doublets can be written as a product of a function of the elastic constants alone and a function containing no elastic constants.

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This paper presents a fracture mechanics approach to the delamination of laminated beams by three-and four-point bending. Interlaminar cracking is assumed to develop from both sides of a bonded beam. Based on the Euler-Bernoulli beam theory (elementary beam theory), the compliance and the total energy release rate are derived, and the stability of the delamination process is discussed. Finite-element computations are then performed to evaluate the compliance and the mode I and II energy release rates. Numerical results are shown to agree well with those based on the elementary beam theory. Finally, through the analysis of the J-integral for the interlaminar crack, it is concluded that the ratio of the mode I to mode II energy release rate is nearly independent of cracking length.

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This paper treats the bending problem of an annular plate with an inner edge which is free and an outer edge which has mixed boundary conditions. It is assumed that the annular plate is subjected to uniformly distributed load on one side of its surface or to uniform shearing load along its inner edge. The above problems are solved by the two methods which were previously proposed by the authors for the bending problems of circular plates with mixed boundary conditions, and the calculated results are compared with each other as well as with results obtained by other investigators and those results obtained by the finite element method (FEM).

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The elastic-plastic fracture tests on the base metal and the weldment of A286 steel, which was one of the candidate structural materials for superconducting generators, were performed at room temperature and cryogenic temperature. It was found that the elastic-plastic fracture toughness J_IC and tearing modulus T_J for the base metal depend on both the specimen orientation and the test temperature. Also, J_IC for the weldment was smaller than that of the base metal at cryogenic temperature. It was also shown from the fractographic observation that the J_IC values can be evaluated by the stretched zone size.

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Thermoelastic problems are reduced to elastic problems by means of the thermoelastic displacement-potential function proposed by Goodier. The generalized Boussinesq solution is widely used in the analysis of elastic problems. This paper discusses a general solution technique for thermoelastic problems of transversely isotropic solids in cartesian coordinates. This technique consists of thermoelastic displacement-potential functions and three fundamental solutions which correspond with Goodier's thermoelastic displacement-potential function and the generalized Boussinesq solution, respectively. The general solution technique for transverse isotropy can be classified into five groups, including a solution technique for isotropy.

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In this paper, nonlinear behaviors such as large deflection, prebuckling and postbuckling are developed for a nonhomogeneous beam. Assuming that the beam is composed of a medium with nonhomogeneous thermal and mechanical material properties in the transverse direction, the one-dimensional transient heat conduction problem for such a nonhomogeneous beam is solved under the condition that the upper and lower surfaces of the beam are kept at constant temperature by the surrounding media. Thereafter, the associated nonlinear thermal deformation fields are analyzed theoretically making use of von Karman's deformation theory under the assumption of Bernoulli-Euler's hypothesis. As for the nonlinear response of the beam, the stationary principle of total potential energy is employed, and the numerical calculations are carried out for the thermal buckling behavior of a simply supported beam, making use of the calculating program for the nonlinear search procedure. The results for the thermal pre- and postbuckling behaviors are shown in the figures, and the influences of the nonhomogeneous material properties are discussed briefly.

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The literature shows that nonlinear stress-strain curves have been obtained in tensile tests of an epoxy-coated hourglass-shaped rock specimen under confining pressures and concludes that this nonlinearity is caused in part by plasticity and mainly by nonlinear elastic behavior. However, in addition to these causes, some contribution of the pore-fluid diffusion is expected. The abovementioned specimen was examined in the previous paper. The present analysis for a noncoated cylindrical specimen (core sample) shows the contribution of the radial pore-fluid diffusion to the nonlinearity and gives the same conclusion as that in the previous paper ; that is, this apparent nonlinearity is small but not negligible. A formula is given to estimate the bend of the stress-strain curve due to the diffusion. Furthermore, sress-strain hysteresis curves are given for the same purpose.

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An effective boundary element method (BEM) for three-dimensional elastostatic contact problems is developed by using the penalty method. Contact conditions of the slip, stick and opening states on the contact surface of the two bodies are assembled into the total virtual work functional and a system integral equation of boundary values is formulated without any increase of the unknown parameters by introducing a penalty coefficient. A BEM based on this formulation is applied to typical three-dimensional contact problems such as the contacts between a cylinder and a block, and between cylinders. The shapes and the displacements are also measured by the experiment of the silicon rubber. The numerical results agree well with the analytical solutions and the experimental results.

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A computer program has been developed to simulate mold cooling in computer-aided engineering for thermoplastic injection molding. The three-dimensional thermal conductive equation is solved by using the boundary element method combined with the finite difference method. A one-dimensional transient heat conductive equation, which represents the cooling behavior of the injected polymer melt, is solved by the finite difference method for estimating cycle-averaged heat flux from the polymer to the mold. Heat flux on the surfaces of the cavity and the runner, temperatures on surfaces of the mold, and heat convections between mold-coolant, mold-ambient air, mold-mold and mold-core are taken into consideration as boundary conditions in the mold cooling simulation. Calculated mold temperatures were compared with experimental results for a mold for a box-shaped molded part. There was a good agreement between them.

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The polymer temperature within the mold was measured with a specially designed thermocouple sensor for validating results computed by a cooling analysis program, which is one of the CAE (computer-aided engineering) programs in injection molding. The thermocouple consisted of 0.1mm dia. chromel/alumel elements and a 8mm dia. Teflon rod, which was used to hold the thermoelements at the gapwise center of the cavity and insulate them from each other and from the mold. The thermojunction was exposed and immersed into the cavity far enough to avoid thermal conduction error. A one-dimensional unsteady heat conductive equation was solved by the finite difference method with consideration of the latent heat and the contact heat transfer between the polymer and mold. Computed cooling curves were compared with experimental ones for various cavity thicknesses and two materials, polystyrene and polypropylene. The predicted minimum cooling times, which were defined as the necessary time for the polymer melt to be cooled to the solidification temperature at the center of the thickness, were in good agreement with the experimental ones for polystyrene, but were about 1.3 times for polypropylene.

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The present paper proposes a determination method of material constants in the internal time theory applied for the arbitrary cyclic plasticity problem. Material constants for kinematic hardening are determined by the stable stress-strain loop by fitting the global integral constitutive equation, while those for isotropic hardeing are obtained as a function of plastic strain length by analyzing the experimental data based on the differential constitutive equation. Cyclic plasticity problem for 12-Cr steel is taken as an example to demonstrate the validity of the present determination method.

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The coupling between the bending and the in-plane deformation under large deflection of annular plates is investigated using a nonlinear programmig theory. The geometrical nonlinear terms in the strain-displacement relations are assumed with not only out-of-plane displacement but also in-plane displacement. The objective function derived from the total potential energy is minimized by the Davidon-Fletcher-Powell method. Numerical examples of axisymmetrical annular plates with clamped inner edge are presented in three cases. The displacements and the stresses are calculated for three boundary conditions of their outer edges. They are clamped edge (Case 1), simply supported edge (Case2) and simply supported movable edge (Case 3). In Case 3, the difference of the results obtained by this method is significant compared with those calculated by the theory considering the nonlinear terms of out-of-plane displacement.

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SQUID (Superconducting Quantum Interference Device) is a highly sensitive magnetic sensor. An apparatus using a SQUID sensor was developed for nondestructive inspection. These measurements were obtained with the SQUID sensor located approximately 150 mm from the specimen. The degradation of thermal aging and plastic strain for duplex stainless steels were successfully detected independently from the magnetic characterization measurements. The magnetic flux density under a high field was found to be independent of thermal aging. Residual magnetization and coercive force increased with thermal aging time. On the other hand, the magnetic flux density under a high field increased with the plastic strain. Residual magnetization and coercive force were found to be independent of the plastic strain.

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This paper presents a unified analysis of in-plane proplems containing elliptic Hole or elliptic rigid inclusion under singular point forces and dislocations of single and dipole types as well as applied stresses and rotation at infinity. The analysis is based on the complex variable method using a conformal mapping technique. The analysis also covers the problems of stress intensity factors (or stress singularity coefficient) of a crack (or rigid line inclusion) under the several singular forces and dislocations at arbitrary finite locations.

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The authors have attempted to develop an analytical method that estimates the variability of structural response by treating the variations in the physical properties of structures by means of the stochastic finite-element method and by treating the random variation in earthquake excitations by means of the random vibration theory, and to further encode the method of analysis. This article describes the formulation of variability of response used in the analytical method, and then shows the results of benchmark analysis with the Monte Carlo method to confirm the accuracy of the analytical method. The floor response spectrum of a reactor building was also analyzed as an example in order to demonstrate the validity of this method.

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An effective design sensitivity calculation technique based on the implicit differentiation method is formulated for isoparametric boundary elements for two-dimensional shape optimization problems, and a practical algorithm for the displacement and stress sensitivities on the boundary is proposed. Efficiency and accuracy of the technique is compared with the semi-analytic method by implementing the sensitivity analysis of typical basic shape design problems. The technique is also applied to the minimum weight design under stress constraints, and an optimal shape of an elliptic hole in a square plate is determined under biaxial uniform tension loading.

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A new AE source analysis using a neural network was investigated. A two-layer network and the artificial AE source signals caused by pencil lead break were used. Detected waveform data obtained by capacitive displadement transducer were processed by the personal computer system. For calculation of the unknown source waveform, the previously trained memory matrix of the network corresponded to the input/output relation. In association with the number of learning data, a small number of data should have estimated incorrect waveforms. But, when additional restrictions were imposed on the memory matrix, appropriate waveforms could be obtained irrespective of the number of learning data, which could be as small as one. The analysis also had such advantages as that relatively low noise data might be calculated if the detected data should include a lot of noise.

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This paper describes an application of neural networks to inverse analyses. The neural networks have been applied not only to qualitative pattern recognition but also to quantitative mapping problems. However, the mechanism of learning and estimating processes, particularly for quantitative mapping, has not been studied so well. On the other hand, nondestructive determination of crack size, which may be regarded as quantitative mapping, has been important in predicting fatigue life as well as in estimating failure probabilities. In the fields of Computational Mechanics and Fracture Mechanics, various identification methods have been suggested so far. However, these methods are not swift and effective for on-line inspection. A BP (Back-Propagation) neural network is applied here to an identification of size and location of a circular defect to demonstrate the features of neural network in quantitative mapping and to investigate its feasibility as an on-line nondestructive inspection.

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The examination of structural characteristics contained in the description of experimental results on the mechanical properties of engineering materials which are often subjected to complex thermomechanical treatments has shown that these data will be well represented with a data model based on Minsky's frame. An important task required for such a representaion is to find appropriate frame designs for individual items in material data descriptions. The designs of some basic frames, such as those for material data, specimen, material, heat treatment, properties, etc., are proposed and discussed. The experimental description of material data in literature with the frame data model has indicated that its expressive power is enough for representing every detail of original data, except for the case where the original data itself is ambiguous. If the frame design, including the choice of the names of frames and slots, is appropriately made, it may play the role of a common description language for a wide range of material data.

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From database consisting of a set of frame-represented material data, data retrieval is made by determining data objects which are subsumed by the object that is also a frame-representation of a query. The discrimination of data can be successfully made down to every detail of data objects such as, for example, the order of successively given thermo-mechanical treatments, their temperatures, and the dimensions of test specimens. Nevertheless, the fact that expected slot values are often missing in original report on the results of material testings impairs the completeness of data retrieval. This problem is coped with through the use of default reasoning, so that to prepare a set of appropriate default rules is an important task to render the database system more useful.

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