Fiber breakage of plain weave glass fabric reinforced plastics (GFRP) under cyclic loading was studied. In order to observe how much the material withstood, a new type of specimens was developed and used. It had two narrow sections which suffered virtually the same fatigue damage. After one section was fatigued to the failure point, the other section was microscopically examined using an optical microscope. The number of broken fibers was counted all over the section. The following conclusions were derived from the experiments. (1) The newly developed specimen is useful for examining fatigue damage state at the final stage just before failure. (2) Under cyclic loading, an appreciable amount of fiber breakage in wefts occurs at the begining of the final stage (cycle ratio : about 0.9). The number of broken fibers rapidly increases just before the sudden failure of the specimen.

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We carried out uniaxial tension fatigue tests on a large number of austempered ductile iron (ADI) specimens. As a result, it was observed that the fatigue life distributions at low stress levels were divided into two groups : a short-life group below 2×10⁶ cycles and a long-life group fractured at near 1×10⁷ cycles. Weibull plots of these fatigue data showed the distinctive feature that the gradient of distribution rose at near 1×10⁷ cycles. After Scanning Electron Microscopy observation of the fracture surface, it was clarified that the short-life group was mainly characterized by stage 2b crack propagation from casting defects and that the long-life group was characterized by fish-eye-type crack propagation. Using a competing risk model composed of these two fracture modes, we could well explain the characteristic fatigue life distributions at low stress levels.

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A machined specimen of spheroidal graphite cast iron (SG iron) has excellent ductility, however a specimen with a cast surface shows very low ductility. This study reports the effect of surface and heat treatment in the production process on the ductility of SG iron with a cast surface. The factors examined are surface microstructures, heat treatment, shot blasting, and machining. Fracture mechanics is applied to the analysis of the effect of surface inclusion. Conclusions obtained are as follows. (1) Ductility of the specimen with a cast surface is much lower than one with a machined surface. The main reasons for this are hardening by shot blasting and surface inclusion. (2)Fracture mechanics may be successfully applied to the analysis of the effect of surface inclusion.

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Mode I interlaminar fracture was studied using double cantilever beam (DCB) specimens of unidirectional carbon fiber/epoxy composites. An improved analytical model was introduced to analyze the crack opening displacement (COD), compliance (C) and fracture toughness (G_I) as a function of the modulus at the vicinity of a crack tip. The COD solution was derived and compared with the COD profiles measured by moire interferometry. The result showed that the COD solution can predict all the important qualitative features of the measured COD profiles ; also, the quantitative agreement was sufficiently good. It is found that the modulus plays an important role in increasing the values of COD, C and G_I.

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The purpose of the present paper is to elucidate inelastic behavior of modified 9Cr-1Mo steel as a candidate material for the next-generation fast breeder reactor and to provide the information for the formulation of a unified constitutive model. For this purpose, cyclic creep, mechanical ratchetting and amplitude history dependence of cyclic hardening were first examined at 550°C. As a result, systematic cyclic creep and mechanical ratchetting behavior were observed under various loading conditions, and little amplitude history dependence was found. Then these results were simulated by three unified constitutive models, i. e. the Chaboche, Bodner-Partom and modified Chaboche models. The simulated results show that these models cannot describe the cyclic creep and mechanical ratchetting behavior with high accuracy, but succeed in describing the inelastic behavior of amplitude variation experiments.

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An experimental investigation was conducted to study the crack growth characteristics of alumina, AD90, silicon nitride, EC-141, and magnesia, MgO, at elevated temperatures in air under static and cyclic loads. The test temperatures were 750, 900 and 1050°C for AD90, and 1000, 1100 and 1200°C for EC-141 and MgO. Crack growth behavior was similar to that at room temperature below specific temperatures, depending on the materials. Above these temperatures, the crack growth mechanism depended on the loading conditions and the materials. For AD90 and EC-141, subcritical or slow crack growth (SCG) was observed on the fracture surfaces. The SCG behavior occurred in a narrower range of the stress intensity factor under cyclic load than under static load. The SCG rate tended to be lower under cyclic load than under static load in AD90, while it was higher under cyclic load in EC-141. For MgO, crack growth resistance was dependent on the loading condition even if the SCG region was not observed on the fracture surface. Based on the experimental results, the importance of the threshold stress intensity factor for SCG, K_ISCG, at elevated temperatures was discussed, and methods for evaluating K_ISCG were proposed.

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In this paper, a caustic experimental method is applied to a simple case of three-dimensional stress analysis. For this purpose, a homogeneous thick plate with a discontinuously distributing load that is divided into two regions across the whole thickness of the plate is chosen as the experimental object. The characteristics of caustics formed by a reflecting light ray at any internal face of the plate are clarified. They coincide well with the theoretical caustic curves calculated using a very simplified optical theory with several assumptions. The features of caustics formed under various loading conditions and theoretical considerations are discussed in detail.

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A three-dimensional mesomechanical simulation method using a discontinuum mechanics model (the rigid bodies-spring model)has been proposed and applied to the numerical analysis of brittle polycrystalline solids containing microcracks. The relationship between microcrack density and elastic modulus under the influence of microcrack closure and surface friction as well as the evolution equation for microcrack density are discussed. The isotropic model in continuum damage mechanics has been improved, based on the results of these mesomechanical simulations.

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The three-dimensional mesomechanical simulation method proposed in the first report of the present study has been applied to the analysis of a brittle microcracking solid under various loading conditions. The validity and the limitation of the existing anisotropic damage mechanics model have been studied by comparing its predictions with the results of mesoanalysis. Based on these results, the evolution equation for the microcrack density in the existing damage mechanics model has been improved. The validity of the improved damage mechanics model has been verified against the results of mesoanalysis.

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The stress field near a corner of jointed dissimilar materials has singularities. In a previous paper, the parameters K_{III, λ1} and K_{III, λ2} for antiplane shear transformation were calculated using the body force method for the problem of an infinite plane with lozenge inclusion under antiplane shear. In this study, this method for antiplane shear problem is applied to an axial symmetry problem, an infinite body with annular inclusion under torsion.

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This paper presents a unified analysis of two-dimensional in-plane problems containing an arbitrary-shaped hole or an arbitrary rigid inclusion under a singular point force and dislocation of single and dipole types, as well as applied stress 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 the stress intensity factor (or stress singularity coefficient) of a crack (or rigid line inclusion) under several singular forces and dislocation at arbitrary locations.

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In the previous paper, noninstantaneities of thermodynamic quantities were introduced in the laws of thermodynamics, to express nonequilibrium processes for continua. Then it was discussed that the time rate of temperature must be newly added to the set of state variables for materials under nonequilibrium processes. In the present paper, the thermodynamic relationships for the above materials are derived and expressed by a newly defined thermodynamic potential and by a dissipation function. Moreover, the constitutive equations are obtained on the basis of the previous results to satisfy the above relationships. The system of basic equations for the continua considering noninstantaneities of thermodynamic quantities is shown, by substituting the constitutive equations into balance laws derived in the previous paper. As a result, it is clarified that the effect of new thermal stress is introduced in the equation of motion and that the velocity of propagation of temperature is finite in the equation of heat conduction according to this theory.

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An effective method of nonlinear finite element analysis is proposed. In the method, a coarse mesh is employed at the beginning of the analysis and elements are refined progressively in an incremental procedure if the amount of absorbed strain energy reaches a given value. Stresses of refined elements are determined under the assumption that they can be interpolated by the same function as displacements. The mixed shape functions are used for "odd" elements having 5, 6, 7 or 8 nodes which are generated by the mesh refinement. To demonstrate the validity of the present algorithm, a series of numerical results are shown, where the calculated load-displacement curves approach the accurate curves as initial meshes are refined progressively in highly distorted areas.

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In this paper, the iterative method which had been reported by Kawano et al. was applied to the elastic-viscoplastic problem. Solutions of this finite-element method using two kinds of algorithms (explicit method and implicit method) were compared with Liu's solutions for an elastic-viscoplastic square cross section subjected to longitudinal impact. The convergence and calculation accuracy of this method were examined. When a constitutive equation in which equivalent stress is decreased rapidly with increase of equivalent plastic strain is used, for example, the constitutive equation of Johnston-Gilman type, it is important to clarify the uniqueness of the solution, especially, in the case of plane stress. We proved that if the following condition is satisfied, uniqueness of the solution exists : dH/dε^^-p > -G(1+ν)/(1-ν).

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Adaptive boundary elements are constructed for elastic stress/deformation analysis of in-homogeneous bodies. Discretized integral equations for each subregion with respect to boundary unknowns and solution errors are combined to obtain linear simultaneous equations for an entire region. The sample point error analysis and extended error indicator proposed previously are employed for error estimation and related refinement of boundary elements. The error level at the internal boundary is adjusted by introducing a parameter which reflects the influence of element error at the outer boundary on solution inconsistency at the internal boundary. Three numerical examples are computed and discussed.

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Al-Li alloys are well known as the materials of low density and high elastic modulus characteristics. We determined the high-pressure phase diagram at 5.4 GPa, and measured the some mechanical properties of resultant supersaturated solid solutions, and observed the interesting elastic behavior, i. e., the bulk modulus decreased with increase of lithium content, in spite of increasing Young's modulus and shear modulus. In order to clarify this property, the compressibilities of the Al-Li super satulated solid solutions (Al-5, 10, 15 mol% Li, prepared by high-pressure processing)were measured using MAX80, the high-pressure X-ray diffraction device set up at the synchrotron radiation beam line at the National Laboratory for High Energy Physics (KEK). The obtained pressure-volume relations were fitted to Birch's equation of state, thus calculated bulk modulus were certainly lower than those of pure Al at a reduction of about 0.6 GPa/mol% Li. On the other hand, the increases of Young's modulus and the shear modulus had been observed in our previous work. Then, the temperature dependencies of elastic constants for those supersatulated solid solutions were measured, and it was found that the trend of variations of elastic modulus against the lithium concentration was maintained in the temperature range of 5 to 290 K. Thus the attractive relationship between the bulk modulus and the Young's modulus was found to be intrinsic.

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The strength of thin-walled rectangular-section beams under three-point bending is discussed. The work is aimed at producing design charts for aluminum extruded beams for automobile door stiffening. Elastic-plastic large-deflection FEM analysis was used. Calculated results were summarized in non dimensional form using the slenderness ratio and restraint factor. The main results are as follows. (1) For flange buckling, the restraint factor by Bleich for axial compression is applicable. (2) For web buckling, the effect of concentrated load on slenderness ratio must be considered. (3) For web buckling, the restraint factor for axial compression is not applicable.

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In order to construct a constitutive equation for polymeric solids, cyclic combined tension-torsion tests were performed using polyoximethylene (POM) at strain paths such as proportional, cruciform, rhombus and circular ones to investigate the effect of strain history on the stress-strain curve. It was shown that : (1) cyclic softening occurs for all strain paths tested here, (2) stress response for all strain paths is influenced by the hydrostatic stress component, (3) stress softening for the circular strain path greatly depends on the previous strain path and (4) stress relaxation after several stroain cycles strongly depends on the direction of the present strain.

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Dynamic behavior of an actuator utilizing shape memory alloy is considered. The actuator is made of TiNi wire which is subjected to pretension and electrically heated. A one-dimensional thermoplastic model is assumed as a stress-strain curve of TiNi wire to discuss the effect of the prestrain on dynamic response. That is, it is assumed that the stress-strain curve is piecewise linear at each temperature around the phase transition points. The material constants of TiNi wire for modeling are determined by uniaxial loading tests at several temperatures. The relation of the prestrain and the maximum displacement is derived from the theoretical model, and it is compared with experimental results. The following results were obtained both theoretically and experimentally. (1) The displacement of the wire, which is the output of the actuator, depends on the prestrain and the heating temperature. (2) The displacement takes a maximum when the prestrain is in the stress-induced martensitic phase. (3) The maximum displacement increases as the heating temperature becomes higher, but there exists a definite limit.

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Thermal shock testing should aim at determining a definite value for the thermal shock properties of materials, and the thermal shock properties should be characterized by two parameters : (1) thermal shock strength, which represents a material's resistance to fracture, and (2) thermal shock fracture toughness, which denotes a material's resistance to crack propagation. For effectual thermal shock testing, it is essential that these parameters should be evaluated directly from thermal loading. The arc-discharge heating method reported in a previous work enables an evaluation of these parameters directly from the electrical power charge. An infrared radiation heating technique proposed here will also make it possible to estimate these parameters directly from the charged electric power. This method can be applied to a wide range of ceramics.

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In designing machine parts or structures which must withstand an impulsive load, it is fundamentally important to know the dynamic deformation of the material at its contact part and the impulsive force generated at that part. In this paper, a new method has been proposed for measuring the impulsive force generated at the contact part in collision. This method is effective for direct measurement of the impulsive force with relatively high sensitivity for normal impact. By means of this method, an impact test on commercial pure aluminum bars with different lengths and spherical ends is performed. From the experimental results, it is found that the generated force and the volume of the deformed part at the contact end increase in proportion to the impact velocity, and that the generated mean stress on the contact part is constant and independent of the radius of curvature of the spherical end and the impact velocity.

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In this paper, theoretical analysis of a three-dimensional transient thermal stress problem is developed for a nonhomogeneous hollow circular cylinder with respect to rotating heat source from the inner and/or outer surface. We assume that the hollow circular cylinder has nonhomogeneous thermal and mechanical material properties in the radial direction. The heat conduction problem and the associated thermoelastic behavior for such nonhomogeneous media are developed by introducing the theory of laminated composites as one theoretical approximation. The transient heat conduction problem is evaluated with the aid of the methods of Fourier cosine transform and Laplace transform. The associated thermoelastic field is analyzed by making use of the thermoelastic displacement potential, Michell's function and the Boussinesq function. Some numerical results for the temperature change and the stress distributions are shown in figures.

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When an isotropic solid cylinder is subjected suddenly to a uniform temperature rise, a stress wave occurs at the surface the moment thermal impact is applied. The stress wave at the surface proceeds radially inward to the center of the cylinder. The wave may accumulate at the center and give rise to very large stress magnitudes, even though the initial thermal stress is relatively small. This phenomenon is called the stress-focusing effect. This paper analyzes the effects of these waves precisely using the ray series. The results give clear indications of the mechanism of the stress-focusing effect in an isotropic solid cylinder.

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A new approach to the convenient method of the analysis of a symmetrical problem in two or three dimensions is proposed utilizing a single scattered light photoelastic image and a sophisticated technique in a computer-aided spline approximation. Two dimensional stress distribution over the whole area of a circular disk specimen under diametric compression is successfully analyzed from an image obtained with a light path inclined to the symmetrical axis of the model.

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This paper describes the influences of circular hole and water absorption on the tension-tension fatigue delamination growth behavior of a carbon fiber reinforced epoxy matrix composite material. The composites used were [0°/±45°/90°]_2S quasi-isotropic and [0°/90°]_4S cross-ply laminates. Dry and wet specimens were used, which had been respectively preconditioned in air and in water at 80°C for two months. Tests were conducted in air for dry specimens and in water at 25°C for wet specimens. Ply-to-ply fatigue delamination behavior was nondestructively and quantitatively examined with a scanning acoustic microscope operating in the reflection mode. In the case of quasi -isotropic laminates with a circular hole, delamination around a hole occurred at the first/second and the second/third interplies. As for flat specimens, however, the edge delamination occurred in the second/third and third/fourth interplies. In the case of circular notched cross-ply laminates, delamination initiated and grew around the hole at the first/second interply, although no conspicuous edge delamination was observed in flat specimens. Water absorption promoted delamination growth in both laminates. Compliance changes with fatigue loading were measured. We discuss the dominating factor in compliance changes especially from the standpoints of fatigue delamination area and the operating fracture mechanisms, including the influences of water absorption on fatigue delamination.

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Measuring elastic properties of thin film on substrates is important in the analysis of residual stresses of advanced 3D LSI. In this study, an approach to for nondestructive measurement of the elastic properties of thin film on the substrate nondestructively with a scanning acoustic microscope is proposed. The approach was analyzed mathematically and was applied to aluminum film on glass substrates. As a result, this approach was proved to be excellent for the objective, and the elastic modulus of aluminum film on the glass substrate was 10% smaller than that of the bulk data.

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The present paper discusses the relation of plastic spin and rotational hardening of the yield surface in large-strain elastoplasticity. The plastic spin, which is introduced to express noncoaxiality between back stress and plastic strain rate, is shown to be identical to the rotational hardening of the yield surface. This paper gives a theoretical formulation of the constitutive equation of elastoplasticity based on the internal time theory and with consideration of effects of plastic spin. The shear problem is taken as an example to demonstrate the effects of plastic spin in Jaumann-rate as well as Green-rate hypoelasticity models, and also to study the effects of plastic hardening laws of isotropic, kinematic and combined hardening models through comparison of the experimental results.

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A method of numerical simulation for hot caliber rolling is proposed, in which deformation of a material is analyzed in an ordinary manner by three-dimensional rigid-plastic FEM, while temperature distribution in the material is calculated using a new combined method of three-dimensional FEM and one-dimensional FDM. First, the method is proven to be effective through analysis of single-pass rolling with various velocities of roll. Next, the method is applied to a simulation of the deformation and temperature of the material in an actual caliber rolling process, in which a round bar is produced from a square billet after 16 passes and strain and temperature distributions in cross sections of the material are obtained. Finally, the calculated shape and surface temperature of the material are found to agree well with measured ones.

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Plastic deformation in steady-state hydrostatic extrusion under high fluid pressure is simulated using the rigid-plastic finite element method. To treat the boundary condition of the fluid pressure in hydrostatic extrusion, the condition of the volume constancy of the fluid is introduced into the functional using the Lagrange multiplier method. The volume constancy of the fluid is expressed as a function of the nodal velocities at the interface between the billet and the fluid for axisymmetric deformation, and the fluid pressure is obtained as a result of the minimization of the functional. Steady-state deformation in hydrostatic extrusion of rods is calculated under various extrusion ratios and half die angles. The distributions of the residual stress in the extruded rods are predicted from those of the stress in the vicinity of the die exit calculated using the rigid-plastic finite element method. The longitudinal and the radial residual stress components are in qualitative agreement with the experimentally obtained values for copper rods.

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In this paper, the changes in residual stress of 10% prestrained or shot-peened carbon steel specimens in the fatigue process were measured by the X-ray diffraction method, and the behavior of slip band initiation and crack initiation in the early fatigue process was investigated by successive observations of replicas of the specimen surface, using an optical microscope and an electron microscope. The residual stress of both prestrained and shot-peened specimens decreased rapidly in the early stage of the fatigue process, and then remained constant up to fracture. The behavior of slipband and crack initiation in the prestrained and the shot-peened specimens is similar. In these two kinds of specimens, many slip bands and cracks originated within grains rather than along the grain boundary.

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Surface topography of a cyclically deformed thin Au plate was observed using a scanning tunneling microscope (STM). Observation was made on the specimens subjected to alternating pure bending with a total strain amplitude of 0.2, 0.1 or 0.05% for various numbers of cycles. The surface became proportionately rough as the number of cycles increased. Heights of the hills and valleys were increased as the number of cycles increased, and they were 20 to 30 nm at most, irrespective of the strain amplitude. However, the average spacing between the hills and valleys became shortened as the strain amplitude increased. At least two slip systems had to be operated for the formation of these rough surfaces. Nucleation of microcracks resulted from concentrated deformation at some of the hills and valleys. Heights of hills and valleys adjacent to the grain boundary were much larger than those inside the grains.

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A simplified method was presented for evaluation of parameters characterizing subcritical crack growth in silica optical fibers of 125 μm in diameter. Water-induced growth of small cracks in the fiber was expressed by means of the power law relationship between crack velocity da/dt and the stress intensity factor K_I, i. e., da/dt = AKⁿ_I. In the method, the parameters n and A were evaluated based on the measurements of failure time, initial crack depth and final crack depth under constant load testing using fiber specimens, where detailed measurements were not needed for changing crack depth in the growth. Application examples showed that the simplified method enables evaluation with as high an accuracy as that of detailed measurements of crack growth.

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The liner of a concrete vessel is strained by concrete deformation. In the design of a liner with anchors, stress analyses of the liner-anchor system are performed to determine the force on the liner and displacement of anchors. Nonlinear simultaneous equations are solved to analyze the liner-anchor system. In the present paper, three methods of analysis--the iterative method, the incremental method and the incremental-iterative combined method--are proposed to solve the nonlinear equations. Obtained results are compared to investigate the method of analysis. It is confirmed that the incremental method offers the most efficient analysis of the liner-anchor system. Usually, all anchors are assumed to have the same dimensions, but anchors of different sizes are often used in actual structures. Liners with two sizes of stud anchors are analyzed, and the effects of different anchors are investigated.

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An automatic FEM procedure based on a geometry-oriented h version is presented for a general plate structure with holes. A simple and efficient method to create the geometry with holes is described. Physical conditions for the structural analysis are given directly in the geometry. Simply by giving the total number of elements, all input data, including the element mesh required for a finite element structural analysis program, are generated and the initial analysis is made. By giving only the allowable ratio of the finite element error, adaptive mesh refinement is made and detailed analysis is carried out automatically. A practical PC program based on the procedure has been developed. Numerical examples are demonstrated to show the validity and effectiveness of the proposed method.

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A finite element formulation using the penalty function method to analyze junctions of plate and shell built-up structures is suggested for an isoparametric shell element. The condition of connection at the junction parts is included in the potential energy functional by the penalty parameter and the interpolating function of displacements. This formulation yields an integral- type stiffness matrix of the junction elements, which can directly evaluate the surface tractions at the junction. The suggested technique is applied to the stress analysis of isotropic and laminated plates with several types of stiffeners, and the validity of the technique is discussed.

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In this study the principle of structural analysis by the ε-method is investigated for a two-dimensional multistoreid and multispan rigid frame with circular members loaded in arbitrary directions in the frame's surface, where the bases of the columns are all fixed. The ε-method applied here is one of the slope-deflection methods and is of practical use in the structural analysis of a rigid frame with circular girders. At the end of the paper, the digital computing program based on the application of the ε-method is developed, and the results of two examples calculated here are given.

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This paper presents a design method of homologous structures using genetic algorithms (GA). The homologous structure keeps its shape according to a functional shape defined in advance. In this work, the homologous structure of the statically indeterminate truss is studied and the problem is treated as a combinational optimization problem using the GA. That is, the selection methods of member's cross-sectional areas for problems that give only homologous functions and that give both homology and minimum weight, are presented.

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