Recent work by the author and collaborators on the plastic behaviour of polycrystalline metals at large strains is reviewed. The crystal plasticity constitutive relations used in the analytical and numerical simulations are first briefly presented. The particular formulation adopted assumes rate-dependent crystallographic slip. We then report some special results where, for FCC crystals with certain "ideal textures", exact closed-form analytical solutions have been obtained for a variety of deformation modes. The implementation of the crystal plasticity constitutive relations in the finite-element analysis of large strain metal deformation processes is then considered. Finally, we discuss current experimental work in our laboratory regarding the determination of yield surfaces for thin sheet metals, and the characterization of the stress-strain response of these materials under complex histories of biaxial deformation.

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This paper deals with application of the stress and displacement field of a wedge disclination dipole in an infinite isotropic elastic medium to analysis of a two-dimensional elastic problem by means of the indirect boundary element method. The disclination dipole has a singularity at its center, and hence we introduce the fictitious boundary method in order to avoid the reduction in the accuracy of the analysis which is caused by the singularity. Consequently, it is found that we can obtain sufficient accuracy if we choose a value 3 or greater as the coefficient of the distance of the fictitious boundary, and it is ascertained that the fields of the wedge disclination dipole can be applied to the analysis of the two-dimensional elastic problem.

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This paper deals with the two-dimensional rolling-sliding contact problem with frictional heat generation on an elastic half-space containing multiple surface cracks. Rolling-sliding contact is simulated as an arbitrarily distributed contact load with normal and shear components, moving with constant velocity over the surface of the half-space. The frictional heat generation at the region of contact is estimated by use of sliding velocity, frictional coefficient and contact pressure. Numerical results of stress intensity factors are obtained for the case of a set of parallel cracks due to Hertzian- and parabolic-distributed loads. The interferential effects on the stress intensity factors with the distance between two cracks, as well as the effects of the slide/roll ratio, frictional coefficient and crack angle, are considered.

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The fracture parameter of an interface crack has yet to be established even for an elastic crack. The CED (crack energy density) was proposed as a crack parameter which enables us to be free from the restrictions on the constitutive equation, and it has been shown that it is applicable, in a unified way, to various kinds of crack behavior in a homogeneous material. Therefore, the CED may also be applicable to an interface crack. In this paper, the fundamentals of the CED for an interface crack are studied. The concrete definition of the CED for an interface crack is given first, and it is shown that the CED can be divided into mode I and mode II contributions that can be expressed by domain integrals without any restrictions on the constitutive equation. Subsequently, the relationships to the conventional crack parameters of the CED are derived. Moreover, the substantial mode I and mode II contributions of the energy release rate are introduced, and their correspondence to the mode I and mode II contributions of the CED is discussed.

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Three-point bending and fracture toughness tests of alumina specimens with various grain sizes were carried out to investigate the effects of grain size on bending strength and fracture toughness. The bending strength increased with decreasing grain size. The intrinsic fracture toughness, which can be obtained by the CSF method, is independent of grain size. On the other hand, the apparent fracture toughness with slow crack growth increased with increasing grain size due to the R-curve behavior, which was found for materials with coarse grains in the BI, FP and CN specimens.

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Thermal stress distribution and thermal strength were examined when butt adhesive joints with rigid fillers in the adhesive were in steady-state temperature distribution. In the analyses, thermal stress distribution in the adhesive was obtained using the two-dimensional theory of elasticity in the case where adherends of the same size and rigid material were kept at a constant temperature and the side surfaces of the joint were surrounded with fluid of a different constant temperature. Numerical calculations showed that thermal stress was tensile near the edges of the interface between the adherend and the adhesive layer, that around the interface area underneath which the filler was located, the thermal stress was concentrated at the periphery of the filler, and that a large amount of thermal stress was generated when the filler size was large. Photoelastic experiments were carried out, and the analytical results were shown to be consistent with the experimental ones.

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The stresses of band adhesive butt joints, in which the interfaces were partially bonded, were analyzed using a two-dimensional theory of elasticity in order to establish the fracture criteria when the joints of dissimilar adherends were subjected to external bending moments. In the analysis, the dissimilar adherends and the adhesive were replaced with finite strips when the interfaces were bonded by the adhesive at two regions. In the numerical calculations, the effect of the ratios of Young's moduli between adherends and the adhesive, the thickness of the adhesive, the bonding area and the position on the stress distributions at the interfaces were demonstrated. As a result, it was seen that band adhesive joints were available when the bonding area and positions were determined taking into account the external load distributions. Experiments were performed on the strains of adherends and the joint strength. Analytical results were consistent with the experimental ones.

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A new algorithm for branch-switching at bifurcation points in the nonlinear finite element method is developed. The procedure is simple and neither eigenvalue analysis nor an alternative cpu-extensive task is necessary for the calculation of buckling modes at bifurcation points. The basic concept is that a displacement corrector vector in the Newton-Raphson iteration can be used in place of an eigenvalue mode which is usually used for branch-switching, due to the high similarity of the governing equations at bifurcation points. Two numerical examples, buckling of a square plate under compressive loading and 'diamond buckling' of a cylinder, are conducted to demonstrate the validity of the algorithm.

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A new formulation is proposed to determine the minimal objective function under inequality constraint conditions. Taylor series expansion of the objective function with respect to design variables is employed for the approximation up to the quadratic terms by use of the Hessian matrix, while linear approximation is employed for the inequality constraint conditions. The objective function is standardized on the basis of the eigenvalue analysis of the Hessian matrix so as to form the hypersphere. The center of the hypersphere is used directly for the minimization of the objective function in the case that the center lies inside the feasible domain of the design variables. In the case that the center is outside the feasible domain, the minimal value of the objective function is searched for as the hypersphere tangent to the hyperplanes which represent the boundary of the feasible domain. The numerical examples in problem of beam vibration show that the proposed method is straightforward and efficient in searching for minimal objective function.

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A general higher-order approximation theory to analyze static and/or dynamic behaviors of laminated composite structures is established. Theoretical characteristics and validity of the theory are made clear by numerical examples. The theory is formulated by using a modified Hamilton's principle for relaxed displacement continuity requirement, after expanding displacements of each lamina using power series in the thickness direction. The independent unknown variables of this theory are displacement coefficients of each lamina and interlaminar stresses. It is shown that the present theory takes account of the previous theories, and improves the inconsistencies of those theories.

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The strength of shaft joints between carbon fiber reinforced plastics (CFRP)and stainless steel bonded with epoxy resin was analytically and experimentally investigated at room temperature and low temperature (-70°C). The distributions of stress for tensile load and thermal stress for cooling in the joint were analyzed by applying the elastic finite-element method. The strength of the joints was predicted by applying the strength laws of CFRP, stainless steel, adhesive layer and their interfaces to the calculated stress distributions. The predicted strength was compared with the experimental strength of the joints. The effects of the overlapped length and diameter ratio between the adherends on the joint strength were examined at both conditions of room and low temperatures. The joint strength for the initial failure is saturated by a certain overlapped length, but the strength decreases with increasing diameter ratio. The final joint strength at low temperature is larger than that at room temperature.

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This paper describes an analytical method for evaluating the elastic properties of three-dimensional fiber reinforced composite materials on the basis of a micro-mechanical analysis of a unit cell structure. The unit cell is a small repeating geometrical unit of fiber architecture. A special feature of this study is that we treat the unit cell as a rigid frame structure constructed of fiber-beam and matrix-beam elements. This analytical structure model can faithfully represent actual fiber composition. For two types of carbon/epoxy three-dimensional composite test specimens cut from an I-beam structure, the tensile elastic moduli are computed by the finite-element method. Comparisons between analytical and experimental results are also made. The results of this analytical method show good agreement with the experimental data.

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We have developed an experimental and computational hybrid measuring system for the purpose of nondestructive detection of cracks embedded in the structural members. The system consists of an infrared thermal video system (TVS-5000), by which the temperature distribution of a body surface can be measured, and an engineering work station (EWS), by which image processing of the thermal image can be carried out. Various methods for heating or cooling the specimen have been examined. Further more an image-processing expert system has been developed to obtain definite images of the defects.

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The photoviscoelastic technique as an experimental viscoelastic analysis is very complicated. The FEM and other methods as numerical viscoelastic analyses are not always reliable. An experimental and numerical hybrid stress analysis for a viscoelastic body is proposed in this paper. In this hybrid method, the experimental photoviscoelastic birefringence and the numerical birefringence are compared for the purpose of confirming the reliability of numerical results of stress and strain in a viscoelastic body. As an example, the thermal stress generated in an epoxy resin beam cooled rapidly is analyzed by this hybrid method.

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