Two-dimensional macrocrack-microcrack array elastic interactions are studied by using homogenization method. The overall elastic moduli of the cracked material are estimated by solving the microscopic problem on the unit cell and they are used in the macroscopic problem. Macrocrack is regarded as a crack in infinite elastic solid, and microcrack array is regarded as locally periodic micro-structure with crack, and the periodic and parallel crack array is configured in the macrocrack tip region. It is found that the effects of interaction by changing of the microcrack parameters that are crack length, position, orientation and loading mode, significantly alter stress and stress intensity factor, then effects of amplification and shielding are observed. Especially by microcrack array rotation, effect of shielding that is toughening by microcracking is caused at an angle, under mode I, mode II or combined mode.

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The present paper djscribes a topological design of two-dimensional structure by cellular automaton. To solve the two-dimensional elastic problem, we use the finite element method. At the application of the cellular automaton, the element of the finite element method is regarded as cell. The cell can be in the two states, namely alive or dead. To generate or eliminate cells, we make a simple local rule based on the equivalent stress. Numerical simulation shows the various topologies of the structure in a prescribed design domain under the various local rules. Also, we discuss how the initial designs of the structure have affect to the final topology.

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A non-probabilistic methodology is presented for the design to enhance structural integrity against the uncertainty in structural parameters. The uncertainty is represented by a convex set of uncertainty variables, in which the fluctuation of uncertainty variables is bounded within a convex hull given as a hyperellipse without consideration of the probability distribution inside. The worst case is determined in terms of unfavorable index defined so as to indicate the degree of harmfulness for the structural integrity. Use is made of the finite element sensitivity analysis and the Lagrange multiplier method for the search of the nucertainty variables to raise the worst case. The worst unfavorable index thus identified is mitigated less than the tolerance limit in line with the structural synthesis based on the first-order approximation of the worst unfavorable index with respect to design variables. The validity of the proposed formulation is investigated through the numerical example concerning with a three-storied portal frame with three braces.

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This paper presents a new scheme for the evaluation of the hypersingular equations for the solution of the classical plate bending problem. The limit of the exterior collocation point of the integral representation for the gradients of the deflection to a boundary point is taken rigorously by combining the evaluations of the integrals over the boundaries in the nighorhood of the collocation point. The final integral representation is free from any divergent term and all the integrals can be evaluated in the standard sense. The interpolation scheme for the deflection is also discussed in the context of the conventional conforming element. The effectiveness of the present evaluation schemes is shown through some numerical demonstrations.

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Elastoplastic problems can be easily solved by the boundary element method. However, even if BEM is used, domain integrals are necessary for elastoplastic problems. The conventional multiplereciprocity boundary element method cannot solve the elastoplastic problem, because the distribution of initial stress or initial strain cannot be given analytically. This paper shows that the elastoplastic problem can be solved without the domain integral by the improved multiple-reciprocity boundary element method. In this method, the distribution of initial stress is interpolated using a boundary integral equation. A new computer program was developed and applied to several elastoplastic problems.

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In this study, a method for the regularization of the boundary value inverse analysis has been proposed. The method is that the fundamental solution in B. E. M. is selected adequately according to the problem to be solved and the rank of the coefficient matrix constructed using the adequate fundamental solution is reduced for the regularization. The optimum condition for solving the boundary value inverse problem is found by using the objective function which is the condition number of the coefficient matrix and the error norm caused by the rank reduction of the matrix. In a numerical example, the optimum condition can be found to the inverse problem governed by twodimensional Leplace and plate bending equation. It was seen that the optimum condition obtained by the proposed method in more adequate than the one obtained by the conventional method from the viewpoint of the objective function. Therefore the proposed method is proved to be very effective for the inverse analysis in B.E.M.

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Formally, we developed new load-support systems that consists of a biconical, alumina-fiber-reinforced plastic (FRP) structure for the superconducting magnet. Safe operation of the superconducting magnet will be jeopardized if the mechanical condition of the load-support system begins to degrade. One of the factors that evaluate the soundness of the supercondducting magnet is the stiffness of the load-support system. Here, it is important to know the relation between the degradation of the stiffness and the growth of defects. For this purpose, firstly, a fatigue test of the load-support system was carried out, and the various defects (matrix cracking and delamination of FRP laminates) were observed during this fatigue testing. Finally, we proposed the application of two non-destructive-evaluation (NDE) methods for the health monitoring of alumina/epoxy load-support systems.

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This paper examines the damage process of unidirectional BN-coated HI-NICALON SiC fiber reinforced glass Composites under tensile loading. The nonlinear stress-strain relation is predicted with the mean matrix cracking interval from replica observation during tensile testing. The prediction gives good agreement with experimantal results. Ultimate tensile strength can be predicted by using a probabilistic fracture model based on the strength distribution data of fibers extracted from fabricated composites. Difference between the experimental strength and the predicted one is examined. The fracture surfaces after tensile testing are observed with SEM and fiber pullouts can be found in fiber rich region more frequently than in matrix rich region.

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Since fiber reinforced composite materials have been applied to main part of structures, the evaluation for their safety and reliability is very important. Acoustic emission (AE) has been widely used as a monitor technique for the damage propagation in fiber reinforced composite materials. However, it is difficult to reveal the damage mechanism from the rsults of AE inspection, because the quantitative relation between the detected AE wave and the mode of damages has not been grasped. In this paper, AE simulation is proposed to help evaluate the damage mechanism by AE. The damage behavior is simulated by finite element analysis using anisotropic damage model based on damage mechanics, and the characteristics of AE are predicted by the analytical results. As an example, the damage behavior of center-notched laminates under uniaxial tensile load has been analyzed and the analytical results have been compared with experimental ones. It is recognized that their results have a good agreement, and that the proposed simulation method is very useful for the evaluation of damage mechanism.

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Structural ceramics are attracting attention in the development of space ships, aircraft and nuclear fusion reactors because they have excellent heat-resistant characteristics. Therefore, various structural ceramics have been developed as heat-resistant materials. Especially, ceramics coating materials are widely used because the materials have the characteristics of both the base materials and the coating materials. However, the ceramics are damaged easily by the thermal stress result from the thermal shock. Therefore, it is necessary to understand their thermal shock properties and to investigate their thermal shock characteristics. In this report, it is discussed to evaluate the cyclic fatigue damage (i.c. crack initiation, crack growth and fracture) for TiN ceramic film during the repeated thermal shock tests. Concurrently with the repeated shocks that irradiated the coating surface with YAG laser, acoustic emission (AE) monitoring was carried out to detect the onset of the thermal shock damage, and the surface appearance was assessed by optical microscope observations. Wavelet Transform (WT) was applied for distinguishing the signals on damage of TiN from a signal on thermal shock in the first 5 msec of the detected signals. After this processing, the features of the AE signals on the damage of TiN film were analyzed. As the results, it was found that the fatigue damage during the thermal shock tests were evaluated by monitoring the 3-D data which represented the relationship between the slope of amplitude distribution of AE signal, AE events and the number of the repeated thermal shock.

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Damage field and stress singularity of a mode I creep crack in steady-state growth are analyzed in the framework of continuum damage mechanics by employing semi-inverse method. A damage field D (x) for steady-state crack growth represented by an undetermined power function γ^l of radius γfrom the crack tip is assumed first, and the corresponding asymptotic stress field of a mode I creep crack is analyzed by solving a two-point boundary value problem of non-linear differential equations. Then, the exponent l of the undetermined damage field is determined so that the assumed damage field may be consistent with the damage evolution equation and the resulting asymptotic stress field. Finally, analytical relations among the exponent p of the stress singularity of the asymptotic stress field and the exponents n and m of the power creep constitutive law and the power creep damage law are obtained. The effects of material damage on the HRR stress field for nonlinear materials are discussed in some detail.

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In order to clarify the effect of hardening treatment on the strength characteristics of foil specimen of SUS 631 stainless steel (thickness : 0.05 mm), various hardening treatments were done to the foil specimen which solution heat treatment was applied at 1313 K for 2 sec (STF material called here). The strength and the hardness of the foil specimens were measured on STF material and hardening treatmented materials by a tensile test and a micro-vickers hardness test. The fracture surfaces of the foils were also observed by SEM. The main results obtained are summarized as follows. (1) Compared with usual hardening treatment method which is"conditioning of austenite +ageing treatment"for a common SUS 631 steel, ageing hardening treatment was appropriate hardening treatment method for the SUS 631 steel foil. Necessary strength, hardness and toughness could be obtained by selecting a suitable ageing condition. (2) From these experimental results, it was shown that precipitation strengthening micromechanism which resulted from ageing hardening treatment could produce a great effect strength characteristics of the steel foils. (3) The tensile fracture patterns of the materials differed with ageing temperature.

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This paper describes the influence of vacuum and water environments on the tensile fracture behavior of three different types of ceramic precursor type fibers : one was an oxide ceramic fiber, γ-Al₂O₃ fiber, or Altex^[○!R] fiber manufactured by Sumitomo Chemicals, and the others were SiC fiber, or Nicalon^[○!R] by Nippon Carbon and Si-C-Ti-O fiber, or Tyranno^[○!R], by Ube Industries. Single fiber tensile tests were conducted in air, in vacuum (2×10^-4 Pa for Altex and 4-5×10^-3 Pa for Nicalon and Tyranno), and in deionized water. The tests were conducted at room temperature. The longitudinal elastic modulus of the fibers were independent of testing environment. However, the fiber strength in vacuum was the highest, irrespective of fiber, and it decreased in the order of in air and in water. Moreover, the strength in water decreased with a decrease in displacement rate : the fiber strength decreased with increasing water content in an environment, and with decreasing displacement (strain) rate. The fiber surface damage that caused a decrease in fiber strength could not be observed by high-resolution, field emission type scanning electron microscopy, because the resolution in z-direction was insufficient. In contrast with this, the AFM has nanometric resolution, and the fiber surface damage caused by synergistic effects of water and tensile loading could be identified, and the degradation and fracture mechanisms of the fibers were discussed.

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The tensile deformation properties due to the martensitic transformation of a TiNi shapememory alloy wire were investigated experimentally. The martensitic transformation started at a gripping part of a specimen due to stress concentration. During the propagation of the martensitic transformation, the martensitic transformation started in the middle part of gauge length. The diameter decreased locally according to the propagation of the martensitic transformation. Poisson's ratio due to the martensitic transformation was 0.45. Poisson's ratio due to elastic deformation of a martensitic and a rhombohedral phase was 0.35.

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An optical high velocity extensometer was developed and used on a new tensile impact apparatus for high speed testing of brittle and ductile materials. The extensometer employed a set of optical fibers mounted on the item being investigated and PSD sensors to measure displacements of the fiber tip positions on the item from which laser rays were emitted. The system was studied with regard to its frequency response and the meter was found to be quick with a response of 100 kHz or more. A tensile impact apparatus equipped with the meter and a piezo gauge was constructed. Results of tests on dumbbell type specimens of PBT/PPE polymer alloy showed that the apparatus was excellent for determination of the force deformation relationship even for ductile materials which undergo necking.

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Uniaxial ratchetting experiments discussed in the 1st report are simulated using a new extension of the kinematic hardening model based on the critical state of dynamic recovery. The extension is formulated on the assumption that the dynamic recovery of back stress, which is decomposed into parts, is activated to some extent in proportion to the magnitude of each part before reaching the critical state. The extension is simple and featured by the capability of representing steady-state ratchetting. The two versions of the model considered previously are also applied to the experiments. It is shown that the extension is effective for simulating the experiments, in which accumulation of strain under uniaxial cyclic loading takes place due to slight opening of stress-strain hysteresis loops as well as viscoplasticity. It is also shown that the effect of viscoplasticity on the accumulation of strain becomes saturated in an early stage of cyclic loading when stress ratio is negative.

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The formability of tubes biaxially loaded in combined axial tension and internal pressure is known to differ from the formability of punched sheets, even if they are made of same materials. The fact suggests that uniform deformation continuing up to diffuse instability is very sensitive to the geometry of a specimen and loading conditions. Plastic instability is defined as the occurrence of the multiplicity in solution, and in general, it is thought not to be influenced directly by loading conditions. Then, the concept of load instability should be introduced for the appropriate evaluation of formability. At a formability test loading path is specified in advance irrespective of specimen strength prior to the test. Under the test the specimen is to meet the state that it cannot sustain the load acting on it. At the instance the loading system loses the control trying to make the loading path fit to the specified path. In this paper the occurrence of loading instability is examined in comparison with plastic instability. With respect to plastic instability the necessary and sufficient condition is proposed based on the concept of multiplicity. The instability appearing at sooner stage is real instability, and it decides the formability depending upon loading condition. The result shows good agreement with experimental formability published in literature.

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The author has performed the analyses of stress and deformation taking into account a surface energy, which exists at the surface and interface dividing phases. In the present paper, the equilibrium formulation considering the surface energy previously deduced by author is used for calculating the stress and deformation. The problem that the surface energy in a half region of a half-infinite anisotropic materials varies is analyzed by using the theory of elasticity. This problem relates with the surface of contaminating, oxidizing or polluting by other materials. Hilbert transform techniques was used for solving an integral equation with respect to an unknown Fourier transform function in the analysis. Consequently, all stress components and displacements were deduced in a closed form. The shear components of bulk stress become infinite at the edge of discontinuity of the surface energy, and then the free suface deforms alike a step. This result may be suggest that cracking occurs easier in a chemically contaminated surface than in a clean one.

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Introducing a rationalized layer element for a two-dimensional elastic analysis of a gradient inhomogeneous material, the reflectance is successfully estimated without any complexities. In the reflection and transmission analysis of elastic waves impinging on a gradient inhomogeneous layer, the difficulty comes out in the evaluation of modified Bessel functions of imaginary order depending on the inhomogeneous parameter. Then the main subject is discussion of a strategic tackle to overcome the difficulty. Rational analysis presented here is the use of a rationalized inhomogeneous layer element in stead of the previously developed element so called LILE. Development of the rationalized new elements and their availability have been explained. As the results, the method by using the new element is very convenient to the analysis of gradient inhomogeneous materials, because the fundamental solutions in the rational analysis are expressed by elementary functions, and the reflectance calculation can be carried out without any use of the modified Bessel functions for any inhomogeneous parameters, as far as it concerns in this study. The trial numerical results by using only one new element, coincide well with the exact numerical results obtained by multistacking layer model of many homogeneous elements.

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A macroscopic solid is modeled as an assembly of atoms, and macroscopic behaviors of a solid are described with microscopic motions of atoms by means of concept of mesodomain. The relationships between mechanical powers and thermodynamic quantities of the solid are discussed by formulating the law of energy conservation derived from microscopic descriptions in the mesodomain. The fluctuation of the body force is introduced in order to express the moment of body force and the radiant heat source microscopically. The obtained microscopic descriptions show that the mechanical powers of the stresses. moment of body force and volume average stress are equivalent to the divergence of the heat flux, radiant heat source and the rate of internal energy, respectively. These equivalencies can be found in the similarities between the corresponding microscopic descriptions of these values. Finally. it is shown that we can introduce the concepts of two extreme material models. that is Thermal Materials and Mechanical Materials.

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Thermal stress distribution of pipe flange connections with a raised-face gasket subjected to heat conduction in steady state are analyzed by using the thermoelastic displacement potential and Michell's stress function based on the axisymmetrical theory of elasticity. In the analysis, pipe flanges, hubs of pipe flange and a raised-face gasket are replaced by finite hollow cylinders, respectively. In the numerical calculations, the effects of the ratios of linear thermal expansion coefficients, Young's moduli and the thicknesses between the pipe flange and the gasket on the contact stress distribution are examined. As a result, it is seen that the thermal stress at the inner and the outer surfaces of the gasket increases with a decrease of Young's moduli ratio and the gasket thickness. In addition, experiments were performed to measure temperature, the variations of axial bolt force and strains at hubs of pipe flanges. Fairly good agreement is seen between the analytical and the experimental results.

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An experimental study was carried out with the aim of improving fatigue reliability for surface modification magnesium alloy casting using three types of specimen consisting of thicker film, thinner film and virgin materials. The fatigue strength of magnesium alloy casting with the thicker film was lower than that with the thinner film. Through fractography using SEM, it was found that the crack initiated at larger round holes in thicker film. Furthermore it could be concluded that the improvement in fatigue strength of surface modified magnesium alloy casting would be caused by forming spinel film of fractal property.

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According to the classification of the failures cause, as more than 90% failures are caused by fatigue and more than 90% of fatigue cracks initiated from the stress concentrated parts of a structural component, it is practically important to investigate the improvement of fatigue strength of notched parts. However, there are few reports on the improvement of fatigue strength about notched specimen based on the viewpoints of fatigue mechanism and the theoretical analysis. Though a hard-facing method is pretty effective for plain specimen to increase the fatigue strength, but not for notched specimen. Then, the authors have considered that the plastic deformation by roller working is one of the best method to improve the fatigue strength of notched specimen. The main results obtained in this test are as follows ; (1) The fatigue limit of notched specimen with roller working increases by 220% than that of without roller working. (2) The increase of the above fatigue limit would be attributed to work-hardening & strain-again due to plastic deformation and compressive residual stress at the surface layer of notched bottom. (3) The non-propagating micro cracks in the depth of 0.4 mm at the notched bottom are observed in the specimen suffered by 1×10⁷ cycles under the stress amplitude of fatigue limit, which has the notched radius as long as 2 mm.

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Fatigue tests of aluminum-silicone alloy were carried out under compressive load using round bars with circumferential notch. Cracks were observed propagating at the notch bottom of the specimens that were not fractured after 1×10⁷ cycles under the repeated compressive load. The change of the stress intensity factor range ΔK accompanied by the crack propagation was studied based on fracture mechanics, considering the residual tensile stress distribution due to the plastic deformation. The applied and residual stresses were calculated by elastic-plastic finite element method. Compared with the estimated ΔK and ΔK_th of short crack taking intrinsic crack length α₀ into consideration, it is verified that in a notched specimens under compressive load a crack initiates but will stop in short, because ΔK decreases in accordance with crack propagation and being below ΔK_th.

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Numerous methods of surface treatment have been developed for purpose of the increase in high cycle fatigue strength and extension of lifetime of the engineering materials in various kinds of environment. In this study, cantilever-type rotating-bending fatigue test in air was conducted using the smooth specimens of alloy tool steel, SKD 61, with three kinds of surface treatment ; that is, TiN coating by PVD method, plasma assisted ion-nitriding and duplex treatment with the ion-nitriding followed by the TiN coating. Fatigue strength of the surface treated specimens was improved as compared with untreated specimen. The highest fatigue strength was the duplex surface treated specimen, followed by the ion-nitriding one and the lowest was the TiN coating one. This tendency was obvious at the region of high stress amplitude and disappeared at low stress amplitude region. Increase of fatigue strength of specimen by surface treatment was due to transition of fatigue crack initiation site from surface to subsurface by an effect of compressive residual stresses occurred at surface layer by ion-nitriding, and barrier to the formation of surface crack nuclei beneath the TiN coating film. The difference in fatigue strength between the duplex surface treated specimen and the ion-nitriding one, of which crack initiation site was subsurface, was discussed by the effect of TiN coating film on subsurface crack growth behavior. It was found that TiN coating film acts as barriers to formation of plastic zone at the front of subsurface crack and retards crack growth twoard surface.

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Fatigue tests are carried out on the notched specimens of forged steels with small defects under rotating bending and it is shown that the fatigue strength of notched specimens having arbitrary sizes of notch radius and notch depth can be predicted systematically based on the concept of linear notch mechanics. The main results are summarized as follows. (1) When the notch radius is larger than a definite size, the fatigue limit is affected and decreased by the existence of defects. This is due to the statistical factor, that is, the difference in sizes of surface areas exposed to the danger of crack initiation. (2) The fatigue limits of plain specimens in the two present materials are smaller than those of some bluntly notched specimens, respectively. (3) The fatigue strength of a bluntly notched specimen having an arbitrary size can be predicted systematically by using a master-curve derived from the concept of linear notch mechanics, including the cases where crack initiations are affected by the existence of defects.

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This paper deals with the effects of specimen orientation and microstructure on small fatigue crack growth in Ti-6Al-4V alloy. Fatigue tests have been carried out under axial loading at a stress ratio of-1 using smooth specimens of annealed (AN) and solution-treated and aged (STA) materials. Specimens were cut from the materials so that the loading axis was parallel to (L-orientation) and perpendicular to (T-orientation) the rolling direction. T-orientation showed higher fatigue strength than L-orientation, which was more remarkable in STA material. In both materials, T-orientation also indicated higher resistance to crack initiation than L-orientation. In AN material, there was a distinct difference in small fatigue crack growth between both orientations : L-orientation exhibited faster crack growth rates than T-orientation at the early stage of crack growth, but STA material showed no significant difference. The orientation dependence of small fatigue crack growth was strongly related to stage I facets developed at the crack initiation site. Although stage I facets were not seen clearly in STA material, the sizes of stage I facets for L-orientation in AN material were significantly large compared to those for T-orientation. Since AN material had a texture with the basal plane (0002) parallel to the rolling direction. the preferred orientation led to faster and extended stage I crack growth for L-orientation.

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Fretting fatigue tests were carried out using a 2618 aluminum alloy to investigate the effect of contact pressure and relative slip range between the specimen and the contact pad on fretting fatigue strength. Irrespective of contact pressure and relative slip range, the fretting fatigue strength was reduced to one quarter of the plain fatigue strength under the stress ratio R=0.0. However, a slight reduction in fretting fatigue strength occured with a decrease in contact pressure and with an increase in relative slip range, respectively. Friction force came to a constant value beyond a certain relative slip range (9 μm) under a pad-span of 30 mm and a contact pressure of 20 MPa. MoS₂+PTFE coating improved fretting fatigue strength. And using fracture mechanics models, a prediction method for fretting fatigue endurance was assessed. The predicted fretting fatigue endurances were in good agreement with the experimental results of fretting fatigue tests.

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The purpose of this research is to apply biomimetic designed composites to artificial structures. Looking at the bio-joint mechanism, the solid fluid composite structure of the cancellous bone is likely to play a great important role in the load transmission. So, the solid-fluid composite model equal to the cancellous bone was made by using honeycomb structure. Static indentation tests were carried out, and in-plane deformation conditions of the solid-fluid composite specimens were measured quantitatively. Experimental results illustrated that the hydrostatic pressure of the fluid phase greatly influenced on the in-plane deformation condition of the solid phase. Consequently, as for the solid-fluid composite models, the compressive load dispersion by the solid-fluid phase interaction was expected.

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The formation of the syringomyelia is caused by some mechanical factors. In Chiari I malformation, it is observed that the flow of the cerebrospinal fluid is blocked by the herniated cerebellar tonsil. However, its influence on the spinal cord is not clarified. In this report, we examine the stress state in the spinal cord when it is deformed in certain bending modes ; one state is that caused by a certain load and the other is in the free vibration. Through numerical examples by FEM, we consider the relationship between the impediment in the flow of the cerebrospinal fluid, the stress distribution and the location of the syringomyelia.

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In this study, the unfolding manner of corrugated simple leaves such as Hornbeam and Beech leaves, was observed from buds to fully opened leaves. Based on these observations, a series of paper models with various vein angles was considered to investigate the effect of vein angles on the unfolding manner of corrugated leaves. By using vector analysis and transformation of co-ordinates, the numerical simulation for the unfolding of corrugated leaves was carried out. A number of characteristic values such as locations in space of veins and of leaf element divided by creases are calculated during unfolding. The kinematic energy during unfolding of the leaf was also estimated to examine the relationship between the vein angle and the energy.

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