This paper deals with the current topics of environmental strength of metallic materials and its methodology from the theoretical and practical viewpoints, including cyclic stress corrosion cracking (cyclic SCC), dynamics SCC, corrosion-product-induced wedge effects, and the mechanical factors controlling crack initiation. Low-frequency variation (stress ratio being near zero)causes cyclic SCC even in materials insensitive to static SCC under a sustained load. Also, the dependence of the waveform on cyclic SCC is opposite that on corrosion fatigue (CF). Small, high-frequency vibratory stresses cause dynamic SCC, with a lower threshold than that of static SCC, K_ISCC; the effects of the vibratory stress range, stress cycle frequency, solution temperature, and crack length on dynamic SCC are discussed. The corrosion-product-induced wedge effects (crack closure) have great potential in influencing CF crack growth, and the mechanisms are discussed. In the case of crack initiation at the bottom of a corrosion pit, the stress intensity factor, calculated on the assumption of a pit being a sharp crack, dominates its crack initiation. The image processing technique, including three-dimensional analyses and the region segmentation according to fracture surface morphology, provide us with powerful tools to investigate the environmental strength of materials.

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In this paper, based on the body force method, a sophisticated way to analyze the semi-infinte body with a revolutional pit under uniaxial tension is presented, and the special fundamental solutions necessary for the analysis are given. The accurate numerical results are shown for the case of the semi-infinite bodies with a semi-spheroidal or drill-hole-shaped pit, and the stress distributions around the pit are discussed.

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The three-dimensional elastic axisymmetric boundary value problem of the torus of a closed hollow circular cross section with varied thickness under uniform internal pressure is analyzed by the indirect fictitious-boundary integral method. The configuration parameters are the mean radius of the torus, the mean meridional radius of the hollow circular cross section, the thickness, and the eccentricity between the outer and the inner circles of the cross section. For uniform thickness, the applicability of Novozhilov's thin shell theory is investigated, and for varied thickness, the leveling of the stresses in the hollow torus with the eccentricity is examined.

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Inverse analysis using the boundary element method is considered theoretically very useful for the qantitative estimation of complicated stresses in a solid material induced by machining, heating and so on. However, a more refined fundamental consideration is still needed for a reliable evaluation of the stresses. In order to fined a more practical estimation method, the authors have carried out several numerical simulations by using rectangular plate models with residual stresses induced by spot heating in the plate. They have also made an improved identification program of the boundary element method. Through typical calculations using this program, they found that unknown residual stress distribution in the plate was identified with enough accuracy from input data of the boundary displacements and tractions.

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An elastic/plastic finite element analysis was performed to provide insight into the minimum specimen size limitations for J characterization in large-scale yielding under a mixed-mode condition. The power-law hardening constitutive equation was employed and a plane strain condition was assumed. The criterion used to judge the degree of dominance was the extent of agreement of the stress field near the deformed crack tip with the results for the small-scale yielding. it was found that the ratio of the minimum ligament L to J/σ₀ for the specimen under a mixed -mode condition necessary to ensure a J-based characterization is required to satisfy the next condition. L≧80J/σ₀ for Mode I tensile specimen, L≧(8050)J/σ₀ for Mode I tensile + Mode II Specimen and L≧50J/σ₀ for Mode II specimen.

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The present paper deals with the heat flow and solid-state phase transformations during the laser transformation hardening of hypoeutectoid steel. A finite-difference computer model was developed to analyze the changes with the time of heat flow, the carbon redistribution in austenite and the subsequent quenching to martensite during laser transformation hardening. The analyzed results were shown in the pseudocolor images on the display. Furthermore, experimental surface transformation hardening was carried out using a square beam of uniform energy distribution, and the results were in good agreement with the theoretical results obtained by the computer model. The transformation hardening process can be also simulated for any given hypoeutectoid steel under any laser irradiating condition. The computer model proposed in the present paper can be applied to determine theoretically the best combination of the process variables for the laser transformation hardening in advance.

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An optimum design technique of a stiffener layout to achieve minimum compliance is developed. A design model of a thin plate with stiffeners is treated as an anisotropic pseudocontinuum and discretized into finite elements. The minimum compliance design problem subjected to constant volume in which the angles of the stiffener arrangement and its density distributions in the orthogonal directions are varied, is solved by a recursive quadratic programming technique. Optimal stiffener layouts of a rectangular plate under some typical loading and supporting conditions are obtained numerically.

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One of the important subjects of bolted connections is the study of the compliance of the clamped parts and the load factor. In this report, the equation of the axial load of the bolts is derived on the premise of separation and nonseparation, and some experiments are carried out for comparison. The results of this study are concluded as follows: (1) The difference in thickness of the clamped parts scarcely influences the axial load. As the eccentricity of load is increased or the initial clamping force is decreased an extreme increase in axial load is more likely to occuer. (2) It has been recognized that the safety limit of bolted connections is partly the separating limit, but it is recognized that it also extends to the center of the bolt hole. (3) The simplified theoretical equation for compliance of the clamped parts and the load factor is derived, and the axial load can be obtained from it because the calculated values agree with the experimental ones.

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The effective Poisson's ratio of laminated fibrous composites shows a peculiar behavior as it becomes larger than unity or less than zero. This behavior can be utilized in the design of composite structure with special functions. The laminate theory, a nonlinear programming technique and a heuristic approach are used to determine the laminate configurations with the maximum, zero and the minimum values of Poisson's ratio of general symmetric laminates. It is found that balanced angle-ply symmetric laminates yield the maximum value and unbalanced bidirectional symmetric laminated yield the minimum value of the ratio. Experimental results show good agreement with the analytical results.

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In this paper, we propose the distribution function of the yield stress to characterize the inelastic behavior of metals. This inelastic model consists of infinitely small cells which have perfectly elastoplastic properties. The distribution function of the yield stress means the content of infinitely small cells. The integral constituitve equation for this model is derived under the combined stress state. To give the effect of the work hardening and softening to the model, we propose the scalar parameter which is the integrated value of inner products of incremental plastic strain vectors along the plastic strain path. This parameter is elaborated by the experimental data of the tensile stress-strain curve and the uniaxial cyclic curves for SUS 304 stainless steel. Biaxial stress-strain relations are calculated with the constitutive equation, including this parameter. It is shown that the work hardening and softening phenomena can be simulated with this constitutive equation and this parameter.

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To formulate the constitutive equations for cyclic plasticity, the subsequent yield surfaces should be examined carefully. In this paper, using a 50μm/m offset strain criterion for yielding, the subsequent yield surface has been measured from the experiment for the initially isotropic material of SUS 304. The experiment shows a translation, distortion, expansion and rotation of the subsequent yield surfaces due to the deformation-induced anisotropy resulting from proportional or nonproportional cyclic loading tension-torsion space. These yield surfaces could be represented by the quadratic form of stresses with fourth rank anisotropic coefficient tensor components. These anisotropic coefficient tensor components are found to be related to the strain amplitude of cyclic loading. As a result, the loading function obtained facilitates the derivation of constitutive equations of cyclic plasticity.

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The finite element formulation of the coupled analysis of plastic deformation and heat conduction is studied for the numerical analysis during the metal forming process at elevated temperatures. As an extension of previous studies, a method of estimating equivalent plastic strain during the steady-state forming process is proposed in the present study, which is applicable to both strain- and strain-rate-dependent materials. As an example of numerical calculation, the coupled heat and deformation analysis for an axisymmetric steady state dieless drawing is performed. The distribution of temperature, plastic strain-rate, equivalent plastic strain and the change of billet shape during dieless drawing are calculated. The obtained results are in good agreement with experimental data. The influence of the work-hardening exponent on deformation and the distribution of temperature is also discussed.

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A solution is given for the frictionless identation of a transversely isotropic layer by an annular rigid punch, where the elastic layer is resting on a rigid foundation. The problem is reduced to an infinite system of simultaneous equations using the method of expressing the normal stress under the punch as appropriate series. The effects of transverse isotropy and identational load on the stress field are studied. The results are compared with numerical solutions for the corresponding isotropic problem.

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The quasi-static loading of a stress-free, initially curved strip, compressed by a flat, rigid plate is considered. The deformation characteristics have been analyzed using an incremental finite element technique. The process involves large displacements, and the strip finally buckles as the central region begins to move away from the plate; snap-through can occur very suddenly. The influence of the end support condition of the strip on the buckling behavior has been analyzed. The assumed end conditions were: rigidly clamped, pinned, and simply supported; as might be anticipated, buckling is not predicted for simply supported ends. It was found that at snap-through, the normalized force for the clamped end condition was larger than that for the pinned end, and the amount of plate displacement was smaller than that of the pinned end support.

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The rigid-plastic finite element method is frequently used to predict the deformation behavior of the materials during the forming processes. The constitutive equation employed is usually restricted to a flow-type one so that the normality of the strain rate to the yield surface is entailed. Thus, the deformation cannot follow the abrupt change in stress history. This often yields the overstabilization of the deformation. In this paper, in order to overcome this situation, a rate-type constitutive equation with a one-to-one relation between the stress rate and the strain rate is employed, and the formulation of the rigid-plastic finite element method is presented. The method is applied to the prediction of the flow localization of the strip under tension. The features of the present results are clarified by comparing the results with those due to J2-flow and the corner theory.

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An elastic-plastic finite element formulation on the basis of the shell theory is given for the analysis of axisymmetric sheet forming, such as hydraulic bulging, stretching with a rigid punch and so forth. Gotoh's plastic constitutive equation with an approximation which is a kind of vertex-hardening theory and his fourth-order yield function for a precise expression of anisotropy are used, as well as the conventional J₂-flow theory. Several numerical examples are presented with the aid of a newly developed computer program in which isoparametric finite elements are used in order to conserve the continuity of the displacement and slope across the element boundaries. Several effects of the X-value and the vertex, as well as the conventional γ^^--and n-value, on the deformation of the shell are demonstrated.

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Moire interferometry is a useful method of measuring small displacement distribution in the whole field of a specimen. However, it is difficult to make diffraction gratings and to measure small strains of less than 10^-3. In order to facilitate the use of moire interferometry, we attempted to mass-produce sheets of diffraction grating by hot-press printing. By transferring the grating of one such sheet, we were able to create a diffraction grating on a specimen. To improve the sensitivity of moire interferometry, we applied a multiplication method to it. As a result, strain of the order of 10^-4 was measured.

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The formability of two sheet steels, SSPDX (0.8mm thickness) and SPMY (0.9 mm thickness), are examined by means of a plane-strain tensile test and an in-plane stretching test. The parameter m of Hill's nonpolynomial yield function is calculated by applying Wagoner's method. The assumption m=2 is recognized for both steels because the difference between effective stress-strain curves of the uniaxial and plane-strain test can almost be neglected. The experimental data of the in-plane stretching test are in good agreement with those predicted by modified M-K theory. Because of less roughness, i.e., a slower growth rate, the limit strain for SSPDX is greater than that for SPMY. The fracture mechanism of the in-plane stretching specimen observed is almost identical to those for isotropic fcc metals reported. However, that of the plane-strain tensile specimen is quite different. The crack is initiated at the center of the specimen by shear deformation and then propagated in the manner of a mode I-type crack. This difference is well explained in terms of anisotropy and strain distribution.

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Supersaturated Al-10 at%Si solid solutions were prepared by high-pressure and temperature techniques. The elastic constants, lattice constants, electrical resistivity, density and hardness of these obtained specimens were measured in each process of isochronal and isothermal aging. At isochronal temperatures of about 100°C°C to 300°C, rapid variations of several characteristics appeared, and the lattice parameters overshot that of pure aluminum. The relation between the Al-matrix and the precipitated phase of silicon and the activation energies for precipitation are also discussed.

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Rotating bending fatigue tests were carried out for three metals: low carbon steel (S15C) with four grain sizes, pure copper and austenitic stainless steel (SUS304). The distributions of crack initiation life N_i, growth life N_p and failure life N_f defined in this study were expressed as a two-parameter Weibull distribution. The statistical scatter of N_i, N_p and N_f distributions increased roughly with the increase of grain size, except the smallest one and with the decrease of stacking fault energy, and decreased with progress of fatigue. The SUS304 showed the highest value of the correlation coefficient between the coefficient of variation η of the N_f distribution and the slope of S-N curves a was expressed as η=c(a)^-b, where b and c are constants.

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