In this paper, the behavior of diffusion creep in Sn-37 Pb as a low temperature melting point alloy during nanoindentation creep test was examined. Creep exponent, n, estimated from the relationship between hardness and indenter dwell time decreases as a function of time and is saturated with n=1. From the observation of the indented surface, the surface was pushed by the indenter in the early stage. However, several grains of tin near indenter were transformed in the last stage. A finite element analysis reveals that the rate of the relaxation of the Mises stress is more rapidly than that of the hydrostatic stress because the multi-axial stresses appear near the indenter. The core hydrostatic stress causes the gradient of chemical potential on the grain boundaries. It implies that diffusion creep is activated during the nanoindentation creep test. The transition of mechanism of creep deformation under the indenter from the dislocation creep to the diffusion creep takes place.

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This paper extensively investigates the collective effects of number of composing grains on meso- and macroscopic plastic deformation characteristics of polycrystalline metals beyond the averaged response. A series of systematically designed finite element analyses based on polycrystal-line models with a common fixed-orientation region surrounded by different numbers of grains is made assuming plane strain two-slip systems. Stress supporting structure (SSS) and the dual flow carrying structure (FCS) are formed as a result of the collective deformation of the grains causing large fluctuation in the grain-wise stress-strain response, which are macroscopically invisible. These meso-scopically extended structures produce “remote effects” where the stress-strain response of a grain in the common region is affected not only by the immediate neighbors but also by the grains located in the distances. The affected region for the remote effect is identified to be containing about 400 grains within the present model. Also clarified is an aspect of the polycrystalline plasticity that the stress and strain fluctuations are mainly attributed to the hydrostatic component and deviatoric component, respectively, on which the duality between SSS and FCS is grounded.

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A third phase, engineered interphase, is introduced between fiber and matrix in fiber/glassy polymer composite to improve the mechanical properties of primary composite. Employing the three-phase model based on nonaffine molecular chain network theory, a parametric study is performed to quantify the effect of stiffness, Poisson's ratio and thickness of the interphase on the localized plastic deformation behavior in matrix, the maximum value of mean stress in interphase and matrix, and macroscopic response of the composite. Furthermore, the effect of interphase is evaluated in the composite blended with randomly distributed glass fiber. The results suggest that the interphase with lower stiffness than that of matrix is useful for the suppression of the onset of crazing in matrix without substantial reduction of the macroscopic resistance. The effect of inter-phase is marked with the decrease of its Poisson's ratio and the increase of its thickness. Moreover, the distance between adjacent fibers is an additional important parameter to enhance the effect of interphase in the later deformation stage.

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In order to reduce the periods of development and investment of materials, it is a very important point to reveal the effect of the local heterogeneity on the mechanical characteristics. However, it is not easy to analyze the effect of the local heterogeneity on microscopic stress using a conventional finite element method. A multi-scale analysis is suggested to estimate the mechanical characteristics for a material with a local heterogeneity. The formulation and the application of the mesh superposition method handling thermal stress by the product process have been reported in this paper. It has been cleared that the proposed procedure has advantage to the thermal stress analysis considering the local heterogeneities. The glass-rich region in a fusion cast refractory has the property of viscoelasticity at high temperature. To estimate the residual stress due to casting process, it is necessary to treat not only thermal but also viscoelastic behaviors. The viscoelastic behavior of the local heterogeneities has been considered with the mesh superposition method and the numerical analysis system has been established. By the system, it is able to estimate the residual stress of the small glass-rich region in a fusion cast refractory and the effect of stress relaxation by thermal cure has been also demonstrated.

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When a crack exists in a structural member, it leads to changes in natural frequencies. Therefore, cracks in structures can be detected by measuring the vibrations in the natural frequencies of appropriate vibration modes. In this paper a crack identification method for plates is presented using both a genetic algorithm (GA) and FEM. The FEM program is developed to calculate the natural frequencies of the cracked plates based on the BFM (Bogner, Fox and Schmidt) plate model since the accuracy of the forward solver is important. In the study, two types of cracks, i.e., internal and edge crack are considered. To identify the crack location and the depth from frequency measurements, the width and the position of the crack in a plate are coded into fixed-length binary digit string. By using GA, the square sum of residuals between the measured data and the dynamic response is minimized in the identification process and thus the crack is identified. To avoid a large number of calculation cost, Response Surface Method (RSM) is also adopted in the minimizing process. The combination of GA and RSM made the identification more effective ad robust. The availability of the proposed method is confirmed by -results of numerical simulation.

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In order to improve the service life of the artificial acetabular cup, it is important to develop the material and design, and to assess the mechanical behavior around the cup. In this study, visual measurement technique, such as electronic speckle interferometry (ESPI) and two-dimensional finite element method (FEM) are employed to investigate the mechanical behavior. First, the influence of the characteristics of cancellous bone and cup thickness on mecanical behavior around the cup was investigated. Good agreement of the cup model analysis has been found between experiments and FEM predictions. In addition, detailed analysis was also carried out by FEM. Following results were mainly obtained. (1) Measurements of cancellouse bone with porous structure can be performed by the ESPI method. (2) There are discontinuities for the displacement distribution of the transverse direction in each boundary regions of cup, bone cement and cancellous bone. (3) The maximum shear stress exists in boundary region of cup and bone cement.

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We irradiated 5 eV Atomic Oxygen (AO) to PEEK sheets with 0.4 mm thickness under tensile load, and estimated strength of the specimen. Three phenomena caused by exposure were observed : (1) appearance of numerous conical pits a few I-μm deep on the specimen surface; (2) reduction of thickness at the irradiated area; (3) change of chemical structure on the surface, which is probably caused by UV generated slightly during the AO irradiation test. As a result of tensile tests, tensile properties after AO irradiation were almost same as those of pristine samples regardless of applied stress. The depth of conical pits was so small and the thickness of layer changed after AO irradiation test was so thin that they did not affect mechanical properties of PEEK sheets. Consequently, residual strength of this material after AO exposure can be estimated by consideration of thickness decrease.

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A computational procedure for analyzing deformation and fracture behavior of solid polymers is developed based on a molecular chain model. In the model, the polymer solid is reprenented by a network of non-linear elastic chains. Van der Waals force and viscous force acting on the chains are taken into account and are approximated to act at the node points of the network. The stiffness equation is derived by employing the principle of virtual work, in which geometrical non-linearity due to large deformation are considered. The chain slippage and the chain session are also taken into consideration. A cellular automaton modeling is introduced to generate the network of polymer chains. The effects of molecularweght distribution and molecular chain session due to ultra-violet degradation are discussed through numerical analysis.

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In this study, stress concentrations near loaded and initial fiber breaks are analyzed for unidirectional composites with matrix yielding and interfacial sliding. To this end, by performing detailed 3D finite element analysis, it is demonstrated that significant nonproportional stressing occurs in the matrix near loaded fiber breaks in contrast to initial breaks, and that the nonproportional stressing induces almost elastic shear deformation in the matrix outside the first nearest-neighbor fibers of loaded fiber breaks. Then, the 3D shear-lag analytical solution derived by the present authors is modified to be applicable to low fiber volume fractions and is employed to dicuss how the nonproportional stressing in the matrix influences the stress concentrations near loaded fiber breaks. The 3D analytical solution is shown to be applicable to loaded, as well as initial, fiber breaks, if the matrix shear modulus in the solution is prescribed by taking account of the nonproportional stressing. It is thus concluded that the nonproportional stressing in the matrix may considerably lower the stress concentrations near loaded fiber breaks.

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Fractal branch-and-bound method has been developed by the authors for the optimization of stacking sequences of symmetric and balanced composite laminates that has two in-plane and two out-of-plane lamination parameters. In the present study, a stacking sequence optimization of an unsymmetrical composite laminate is examined. In the unsymmetrical laminates, nine lamination parameters including three coupling lamination parameters are not zero. Using tetrahedral fractal patterns of feasible laminates of in in-plane and out-of-plane lamination parameter coordinates, and a tetradecahedron fractal pattern of a coupling lamination parameter coordinates, fractal branch-and-bound method is applied to optimize the stacking sequence of unsymmetrical laminates. This new method is applied to a stacking sequence optimization problem of a maximization of buckling load of cylindrical shell structure. As a result, the method is successfully applied, and the practical optimal stacking sequence is obtained.

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This paper discussed fatigue behavior of plain-woven CFRP using very thin and wide tows called spread tows. Tension-tension fatigue tests were conducted and internal damage was observed by using an optical microscope. Three points bending tests were conducted to measure critical energy release rate and threshold energy release rate range. The experimental results showed that the fatigue life of plain-woven CFRP using spread tows was longer than that of conventional plain-woven CFRP. As the fatigue tests were conducted at cyclic maximum stress of 600 MPa (about 65% of tensile strength), we could not observe any cracks in new type plain-woven CFRP that was subjected to 10⁶ cyclic loads. The critical energy release rate and the threshold energy release rate range at spread tow in the composite got higher than those at conventional tow. The ply failure strain, which was the crack formulation and propagation criterion, was calculated by assuming that a part of plain-woven CFRP using spread tows was (0/90) _s cross-ply laminate. It was concluded that crack was constrained by using spread tows for the composites.

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In order to investigate the propagation behavior of an internal crack in surface treated steel, rotaing bending fatigue tests were carried out for a radical-nitrided bearing steel. The fracture occurred from a specimen surface under high stress levels, whereas a fish-eye fracture occurred under low stress levels. Consequently, S-N curve was duplex S-N one. A circular trace was observed inside the fish-eye when the fracture occurred under two-step variable stress amplitude test. It was suggested that the trace was formed by the change in stress amplitude. Moreover, from the change in the trace size depending on the stress level and the number of stress cycles, it was concluded that there is a fatigue limit for the internal fracture meaning the limit for crack propagation and most of fatigue life the internal fracture was occupied by the growth life of a small internal crack.

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In this paper, we propose a method to quantitatively estimate the decrease in threshold stress intensity factor (SIF) range due to high SIF, that is observed for some materials in constant maximum SIF fatigue crack growth tests. The parameters cased for the simulation were inversely determined with the aid of Genetic Algorithm. The validity of our method was shown by comparing the simulation data with experimental data for embrittled S 55 C.

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We evaluated the distribution of tensile strength in polyimide covered silica capillary tubing. We also investigated the effect of the polyimide covering on the tensile strength and analyzed the effect of the initial non-penetrated crack length on the crack propagation by using FEM. The diameter of silica capillary tubing was 150 μm. The surface of the silica capillary tubing was covered with a 12-μm-thickness of polyimide. The length of the tensile specimens was 400 mm. The relation between the tensile strength of silica capillary tubing and the fracture probalility was distributed into a strong and a weak group. The tensile strength distribution in the strong group was the original strength distribution caused by manufacturing deviation, and that of the weak group resulted from micro-cracks introduced during or after the specimen manufacturing process. We can predict the strength of the silica capillary tubing using the strength of the optical fibers, because the strength properties of the silica capillary tubing with the polyimide covering were the same as the static strength properties of the optical fibers. We found that the polyimide covering did not improve the tensile strength of the silica capillary tubing, but it was effective as an overcoat. Using FEM analysis, we found that the non-penetrated crack in polyimide covering did not reach the quartz surface during handling, and crack propagation was restrained near the interface because Young's modulus of the polyimide was smaller than that of quartz. When applying silica capillary tubing, we recommend that more attention should be paid to the micro-crack formation on the surface of the quartz than to the crack growth in the polyimide covering.

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Platinum and its alloys are widely used for glass melting apparatus and the materials used for the apparatus require high temperature fatigue strength as well as high temperature creep strength. Authors reported that Oxide Dispersion Strengthened (ODS) Platinum has high resistance to creep rupture in the previous paper. In order to clarify the details of fatigue fracture behaviors of ODS Platinum, various ODS Platinum materials were evaluated with regard to tensile and fatigue tests. Through the evaluations, following results were obtained. (1) High fatigue strength results in short inter-dispersoid distance in low cycle region and high Grain Aspect Ratio (GAR) in high cycle region. (2) Fracture mode of low GAR material is trans-granular fracture in low cycle region and inter-granular fracture in high cycle region. Different from low GAR material, fracture mode of high GAR material is trans-granular fracture for both low and high cycle region. (3) High temperature fatigue strength of ODS Platinum in low cycle region is in inverse proportion to the inter-dispersoid distance as well as high temperature tensile strength. An increasing in OROWAN stress is a measure to improve the strength in the low cycle region. In the high cycle region, fatigue strength is in proportion to GAR therefore increasing in GAR is a measure to improve the strength in the region.

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A partial differential equation is derived for the macroscopic total strains of a material containing mutual perpendicular penny-shaped cracks with respect to the crack densities of the cracks by using the incremental form of the Mori-Tanaka theorem. By solving the partial differential equation, the macroscopic total strain, the average interaction stress and hence the macroscopic elastic moduli are formulated as a function of the crack densities of the cracks. On the contrary to the results obtained by the ordinary Mori-Tanaka theorem, the resultant macroscopic elastic muduli asymptotically tend to zero as the crack densities of the cracks increase. The present results are in good agreement with the numerical results by means of the differential scheme when the magnitudes of the crack densities of the mutual perpendicular penny-shaped cracks are equal to each other. The volume fraction of the randomly oriented penny-shaped cracks in physical meaning is obtained by comparing the resultant interaction stress with that derived from the Mori-Tanaka theorem.

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The X-ray diffraction technique for stress measurement can nondestructively determine residual stress in a localized surface layer of polycrystalline materials. In this method, the stress is determined from measured lattice strains using the X-ray elastic constants. Since the lattice strains of a particular lattice plane in the crystal grains are measured selectively, the X-ray elastic constants are different from the macroscopic constants of isotropic materials. The equations are derived for calculating the X-ray elastic constants for polycrystalline materials having arbitrary crystal structures from single crystal data. The Reuß and Kröner models are used for the premise on the deformation of polycrystal. Measured X-ray elastic constants of steel, α-silicon carbide and α-alumina, which have cubic, hexagonal and trigonal structures respectively, were compared with the theoretical values. The values calculated using the Kröner model agreed most closely with the measured values.

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A determination method for elastic-plastic material constants using plural triangular pyramid indenters, which was previously proposed by the authors, is improved in this study. The interpolation function Π_int is simply determined based on two theoretical solutions for conical indenter penetration : the elastic solution and the rigid/perfectly plastic solution. The function Π_int gives the relation between reduced Young's modulus E^*, load curvature C and representative stress σ_r. On C/σ_r, versus E^* /σ_r plot, the elastic solution is expressed by a linear function and the rigid/perfectly plastic solution by a constant value. Both solutions give the extremes for Π_int. With this Π_int and another function, which relates representative strain ε_r to indenter apex angle φ, the stress-strain curve is identified. The good experimental results for real materials were obtained by this newly improved method.

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The final goal of this study is to apply a shock absorber based on plastic deformation of aluminum tube to an elevator buffer. First, in order to study characteristics of axially crushed tubes, various aluminum tubes were compressed on four types of dies. As a result, these caused the three modes of progressive buckling, tearing and inversion. It is concluded that the load-displacement curve of the inversion mode has ideal shape as shock absorber and its inversion load depends on the thickness of the tube. Secondly, energy absorbing mechanism of inversion mode was made clear with finite element method (FEM), and its details show two kinds of energy, frictional dissipation and plastic dissipation produced by meridional bending and circumferential stretching. A theoretical expression for calculation of the inversion load is derived from the virtual work theorem, the prediction from which agrees well both results of experiment and FEM. It is also discrived that use of molybdenum disulfide improves reproducibility of the inversion mode and its load-displacement curve.

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