Multi-scale computer simulation technique is applied to the study of the dislocation behavior in nickel base superalloys. The keys of this simulation are the modeling of the interactions of dislocations with γ' precipitates, and the treatment of complicated behavior of dislocations in complex microstructure of nickel base superalloy. The strength of a γ' particle as an obstacle to dislocation motion is calculated by means of molecular dynamics (MD) simulations. The strength of a γ' cube is modeled basing on the consideration of the energy increase by the formation of anti-phase boundary due to cut of the γ' phase by a dislocation. These models are implemented into the dislocation dynamics (DD) code, which is very successfully applied in this study to the simulations of the evolution of the dislocation microstructures with different γ' obstacle arrangements. The present simulations clearly demonstrate that the multi-scale computer simulation strategy has capability to predict mechanical property such as stress-strain relationship starting from atomistic-level information on the dislocation-obstacle interaction. This technique should be very promising to understand the fundamental mechanisms of dislocation behavior in other materials.

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Liao and Chwang proposed a new boundary element method using homotopy for nonlinear transient heat conduction problems in orthotropic solids. This study is concerned with an application of this approach to anisotropic solids. Mathematical formulations of the boundary element method are presented in detail for two-dimensional nonlinear transient heat conduction. Computation is started from the initial stage subject to a given initial condition, and advanced by an iterative procedure until the root mean square (RMS) of the residual is a minimum or the rate of change in RMS is less than a tolerance. The proposed solution procedure is applied to some typical examples, and the usefulness of the proposed BEM is demonstrated through discussions of the results obtained. Emphasis is placed on comparison between the present scheme and isotropic solid scheme of the Liao-Chwang method.

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Off-axis deformation and fracture of GLARE-3, a cross-ply hybrid laminate of glass/epoxy laminae (GFRP) and aluminum-alloy sheets, have been examined at room temperature (RT) and 100°C (HT), respectively. The classical laminated plate theory (CLT) was applied for describing the off-axis tensile behavior of GLARE-3 laminates. Irrespective of the off-axis angles and test temperatures, the tensile stress-strain curves show a clear transition from linear response to nonlinear one. This is due to the yielding of the aluminum-alloys layers. The elastic modulus and static tensile strength decrease as the test temperature increases for all off-axis angles. Also, the flow stress at HT becomes smaller than that at RT. For θ = 15, 30 and 45°at HT, a sudden decrease in the flow stress takes place just before the ultimate fracture occurs. This fracture mode may be caused by the reduction of the adhesive strength between the GFRP and aluminum-alloy layers. A modified CLT model, which takes into account an incomplete failure in the GFRP layers, favorably describes the characteristics of the nonlinear deformation behavior of the GLARE-3 at RT and HT, respectively.

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The so-called 'visible length' under the surface of a short fiber reinforced composite was examined, assuming that fibers under the composite surface could be observed. The fibers under the surface are overlapped by other fibers. The length of the part between other overlapping fibers is the visible length. Relative position of the fiber in the composite can be classified into six categories when the fiber was observed from the composite surface. In each category, projection length of the fiber to the composite surface was calculated. The result was substituted for the method proposed before and the visible length distribution was obtained. It was found that the average visible length in the composite dose not significantly changes, if the average fiber length exceeds 30 times of the fiber diameter. Furthermore the influence of fiber volume fraction on the visible length was clarified.

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The characteristics of residual stress and deformation of thermal sprayed plates, that are the most important property from the view point of production technique for preventing the cracking and delaminating of coatings, have not always been made clear. In this paper, the residual stress and deformation behaviors of rectangular plate, induced by the inherent strain of coating layer due to thermal spraying, was analyzed using the finite element method. It was confirmed that the dimensionless parameters of σ·(1-v_c)/(E_c·ε₁) and u·T/(L²·ε₁) was useful for presenting the residual stress and deformati, on characteristics of thermal sprayed plates. (σ: residual stress, v_c: Poisson's ratio of coating, E_c: Young's modulus of coating, ε₁: inherent strain of coating layer, u: displacement. T: thickness of substrate and L: length of substrate) It was found that the inherent strain of coating layer, that was calculated by the deformation of thermal sprayed plates, was almost constant in case of the atmospheric plasma sprayed CoNiCrAlY over IN 738 LS substrate.

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To introduce a large and deep compressive residual stress with the Shot Peening method, the authors conducted an experiment using Vacuum Carburized and Shot Peened or Stress Shot Peened specimens, and investigated the influence of Arc height (Ah), Shot radius (R), retained Austenite (γ_R) content, Strain Induced Martensite (M_Q) content and loaded stress (σ_pre) upon compressive residual stress (σ_r) systemically. The major results obtained are: (a) The surface residual stress (σ_rs) and the maximum compressive residual stress (σ_{r max}) were almost dependent of Ah/R. (b) There is a little influence of γ_R content after Shot Peening upon σ_rs and σ<r max>. (c) There was hardly any influence of M_Q content uponσ_rs and σ<r max>. (d) Approx.50% of σ_pre was introduced as σ_rs and σ<r max>. (e) Further, it was found the a linear relation exists between Ah/R, γ_R & σ_pre and σ_rs (σ<r max>).

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Low-cycle thermal fatigue tests were carried out on aluminum alloys, AC2B-T6. As test temperature makes great effects on mechanical properties, more efforts were focused on the temperature range to find out relation between life and constraint factor of thermal strain. The investigation has turned out that the test specimens which were subjected to temperatures higher than the tempering temperature, and those which were not, greatly differ in mechanical properties Microstructures of test specimens for three temperature ranges were examined by TEM. Fracture surfaces were also observed by SEM. The observation of microstructure has revealed that the highest and lowest temperature ranges greatly differ in the shapes of precipitates and precipitate density, and that the difference make great effect on life. Fracture appearances were also clarified by the investigation. Lastly, test specimens were overaged to study the effects of tempering temperature on life, which turned out to be very effective for lengthening life.

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The most popular aluminum alloy, AC2B-T6, was tested for thermal fatigue with the center of strain amplitude offset to take realistic engine running conditions into consideration. Test specimens were overaged to study the effects of tempering temperature on life, which turned out to be very effective for lengthening life. In the TEM microstructure observation, attention was focused on precipitates, and the average size and number of precipitates were measured. The effects of temperature, loading period strain amplitude on the characteristics of precipitates were studied to establish relation with fatigue life. As a result, it was found that the average size of a certain type of precipitates has a strong correlation with fatigue life, and was concluded that not only material properties but also microstructure should be studied to develop an aluminum alloy.

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Fatigue tests of vulcanized natural rubber were conducted under displacement-controlled conditions. The specimens were of three types: smooth specimen, specimen with an artificial surface defect of 0.2 mm in diameter, and specimen with an artificial through-thickness defect of 2 mm in length. In smooth specimens, a fatigue crack started from natural defects of about 0.15 mm in size, and grew as an internal crack, and then became a through-thickness crack. The spring constant of the specimen decreased slowly in the range of about 80% of the total life (Stage A), followed by a rapid decrease (Stage B). The transition from Stage A to B took place when a crack penetrated through the thickness. The rate of fatigue crack propagation is expressed as a second-power function of the J-integral range both for surface cracks and through-thickness cracks. The J integral was evaluated from the crack-center opening displacement.

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A J-integral equation, J = f_σ·H·f_W·f_θ·πa/Q/E', at surface and maximum depth point of a three dimensional surface crack under bending loads at elevated temperature for elastic-plastic analyses was developed. In this equation, the applied load and the crack shape are introduced to the J-integral value, and the fatigue crack growth behavior can be simulated precisely. The parameter f_σ is the function of applied load; H is the function of aspect ratio a/c and the ratio of crack depth to plate thickness a/t; f_w is the function of the ratio of crack length to plate width c/W; f_θ is the function of radiation angle to identify position along the elliptic crack front θ; Q is that of complete elliptic integral of the second kind E(k); E' is an equivalent elastic modulus. The equation is based on the finite element analysis completed by the authors with the surface cracked large plate specimen a few years ago. This new equation can be used to develop analyses given by the finite element method for 3-D semi-elliptical surface cracks in finite elastic-plastic plate, such as the wall of a main vessel of a fast breeder reactor, subjected to bending loads. A wide range of configuration parameters is included in the equation. The aspect ratios, a/c, ranged from 0 to 1, the ratios of crack depth to plate thickness, a/t, ranged from 0 to 0.7, and c/W &lne; 0.8. The values of the J-integral computed by the equation were compared with those from the finite element analyses. The comparison showed that the mean errors were within ±3.9%. We also developed a method for using the J-integral equation to simulate the 3-D surface fatigue crack growth, and how the fatigue crack grows under bending loads at elevated temperature for SUS 304 steels at 550°C and SUS 316 FR steel at 600°C. The curves of crack aspect ratio, a/c, vs. the ratio of crack depth to plate thickness, a/t, by the proposed method describe the experimental data well.

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In this study, the general solution of stresses is derived for a T-shaped junction of two thin plates with an adhesion crack. A shear force is applied on the crack surface. The analysis is based on the supposition that the stresses in each plate can be approximated by a plane stress condition. The results obtained are verified by numerical calculation of the finite element method. A singular stress field is obtained from the solution for the neighborhood of the crack.

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In this study the plane strain crack problem for a layered piezoelectric plate with a finite crack is considered. The laminated slab is made of a piezoelectric slab bonded between two elastic layers of different physical properties. The Fourier transform techniques are used to reduce the problem to that of solving a singular integral equation. The singular integral equation is solved by using the Gauss-Jacobi integration formula. Numerical calculations are carried out, and the main results presented are the variation of the energy density factors as functions of the geometic parameters, the material properties and the electrical boundary conditions of the layered composites.

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Cellular materials consist of lattice-like microstructures are usually treated as continua which have equivalent macroscopic mechanical properties for structural analysis. Whereas the linear theory that estimates the equivalent properties for composites include cellular materials is mature, the theory and the methodology for the nonlinear analysis of cellular materials remain active fields of research. Then, in this context, we apply the homogenization method, which utilizes multiple scales and realizes macro and micro coupling multi-scale analysis, to cellular materials. Frame elements are employed in the multi-scale analysis based on the homogenization method since it is rational from computational viewpoint for discretizing the lattice-like microstructure. Finally, we show some numerical examples of the nonlinear multi-scale analysis of cellular materials in order to validate our multi-scale analysis.

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A service cable with flat wires and an woven tube for an sensor of the sliding door was under consideration using the post-buckling behavior in pure bending of thin strips with arc cross section in order to keep quiet and to miniaturize the service system. The post-buckling deformation model was proposed and the post-buckling deformations of the flexible structure were approximately analyzed using the strain energy method for an infinitesimal strain problem of large deformation. The stability of the post-buckling was discussed checking the second variation of the total potential energy. The theoretical predictions were compared with experimental results about the relationship between the radius of curvature under post-buckling and the radius of circular arc and the pure bending moments of the barrel-shape and the saddle-shape deformations, and the correspondence was found to be acceptable.

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When Thermal Barrier Coating (TBC) is subjected to a high-temperature environment, thermally grown oxidation (TGO) layer is grown at interface between top coating and bond coating. The existence of oxidation will bring reduction of coating cohesion. The aim of this study is to clarify TGO growth process under variation of temperature condition. For this purpose, one-stage variation of temperature tests, which is one that after heating TBC specimen at constant temperature 973 K during a constant period 500 h, specimen is heated additionally at 1 173 K, for instance, was conducted. TGO growth process was examined by SEM observation of a cross section of the aged specimen. As some results obtained, (1) TGO growth process had no effect of difference in a kind of substrate material. (2) TGO layer was not formed at aged temperature below 973 K. In aging temperature range between 1 073 K and 1 173 K, Al₂O₃ as TGO layer was formed at interface between top coating and bond coating layer.(3) TGO grew under post-aged temperature, which is higher than pre-aged temperature. And then, TGO growth law at a constant temperature is also effective to complicated condition as a variation of temperature focused in this study.

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A micro-indentation test is useful for evaluating mechanical properties of a micro-structure. But because the measurement values are very small, there are some significant error factors. In this paper, the influences of a work-hardened surface which has been made by a mechanical polishing were investigated using experiments and finite element analyses. The indentation results on a ductile material, like an annealed copper, are very sensitive to a work-hardened surface. The indentation's shape varies, according to a penetration depth, from piling up to sinking in. It is important to improve the elastic modulus by changing the calculated contact area to a measured value by the proposed method. However the hardness of a material is not able to be improved by the measured contact area, so it would be misleading to assume that these results are applicable to a material which is entirely as hard as the work-hardened surface. In order to evaluate properties of a material accurately, an electrochemical polishing is needed after mechanical polishing to remove the work-hardened surface.

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