Fatigue properties were examined for four types of JIS aluminum alloys for use in welded structures, namely, A5038P-O, A7N01P-T6, A7N01S-T5 and A6N01S-T5. The fatigue strength was found to be independent of the heat and thickness of the materials. It was highest for 7N01 alloy under both T6 and T5 conditions and was lowest for 6N01-T5 alloy. A unique relationship existed between the fatigue limit and the tensile strength for aluminum alloys and different steels. The fatigue crack growth rates of aluminum alloys were equivalent to those of steels as well as that of copper, when they were evaluated on the basis of a converted strain intensity factor range, ΔK_eff/E, or the ratio of effective stress intensity factor range to Young's modulus of the materials.

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Fatigue properties of butt-welded joints were investigated for four types of aluminum alloys, 5083-O, 7N01-T6, 7N01-T5 and 6N01-T5. The fatigue strength of the butt-welded joints were nearly the same for the four alloys and generally lower by a factor of about three than those of base metals. The fatigue strength after 10⁸ cycles was independent of the tensile strength in the case of butt-welded joints, while it was proportional to the tensile strength in the case of base metals. By comparison with the typical structural steels. HT80, SM50B and SUS304HP, a unique relationship was found between converted elastic strain range, Δσ/E, and fatigue life, N_f, for the welded joints of the steels and the aluminum alloys investigated, where Δσ and E are stress range and Young's modulus, respectively.

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A series of creep-fatigue tests were conducted using 316FR steel at 650°C in a very high vacuum environment of 0.1μPa. The test results indicate a creep-fatigue behavior which is completely free from the environmental effect of the air. In general, creep-fatigue life reduction occurs when the tension time is longer than the compression time. After the creep-fatigue tests, the fracture surfaces were investigated using a SEM. A good correlation exists between the creep-fatigue life and the fracture mode. When the fracture mode was predominantly transgranular, no life reduction occurred. On the contrary, when it was predominantly intergranular, a significant life reduction was observed. The overstress was experimentally investigated and the relation between the overstress and the inelastic strain rate was obtained. The creep-fatigue life evalution model based on the overstress was applied and it was shown that it predicts the life accurately.

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Bridging and interlocking elements, which are responsible for the stress shielding effect, are frequently observed in the wake of fatigue cracks. The crack growth curves arranged by the crack tip stress intensity factor K_tip (da/dN-K_tip curves), where the stress shielding effect is taken into consideration, almost coincide regardless of loading history, while those arranged by the apparent stress intensity factor K_app (da/dN-K_app curves) significantly depend on the loading history. The fatigue crack growth resistance increases with increasing grain size. The main reason for this grain size dependence is that the stress shielding effect becomes significant with increasing grain size. The crack growth curves arranged by K_tip almost coincide regardless of grain size.

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Chromium nitride (CrN) has good corrosion resistance in addition to its good electrical and mechanical properties. A decrease in the number of defects such as pinholes or voids formed during deposition is required for improvement of corrosion resistance and corrosion fatigue strength of coating materials. A multistage physical vapor deposition (PVD) method was proposed in order to fabricate dense thin films. In an anodic polarization test in aerated 2%H₂SO₄ solution, CrN thin film deposited on 0.37 wt.%C steell using the multistage PVD method showed better corrosion resistance than that of the specimen coated using a conventional method. This is due to a decrease in the number of small defects in coating film by the multistage deposition. Evaluation of corrosion fatigue strength in the multistage coating steel was performed by means of a cantilever-type rotating-bending fatigue test in 3%NaCl solution. Corrosion fatigue strength of the multistage coating steel was improved as compared with that of the uncoated steel, but the increase in fatigue strength was less in the multistage coating method than the conventional method, contrary to the experimental results obtained from the anodic polarization test. It was pointed out that corrosion fatigue resistance is dependent on not only the number of defects but also the shape of large defects in the coating film.

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We describe an investigation on the fatigue fracture behavior of an SiC whisker reinforced A6061 aluminum alloy fabricated by a squeeze casting process under combined tension/torsion loading at room temperature. Attention was focused on in-phase and out-of-phase tension/torsion loading. The tests were conducted under a load-controlled condition keeping a constant value of the combined stress ratio, α=τ<max>/σ<max>. Irrespective of loading condition, the mechanical properties of the composite including fatigue strength were superior to those of an unreinforced A6061 alloy, not only under uniaxial loading, but also under combined in-phase and out-of-phase tension/torsion loading. In the case of the unreinforced matrix material, the fatigue strength under out-of-phase combined loading was smaller than that under in-phase loading. However, for the composite, the fatigue strength under out-of-phase combined loading was higher than that under in-phase combined loading. The crack initiation and propagation behavior was closely examined using a surface replication technique, and the fracture mechanisms under in-phase and out-of-phase combined loading were discussed.

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Fatigue crack bending and growth behaviors were studied under mixed-mode conditions, using annealed and fatigue slant precracks with a center-hole notch. The crack growth direction was estimated from the stress intensity factors K_I (mode I) and K_II (mode II) evaluated from the discontinuous displacements along the precrack, using the maximum tangential stress criterion, and it was in good agreement with the measured ones. The fatigue crack propagation rate during bending was controlled by the effective stress intensity factor range ΔK_eff using K_I and K_II, in which a total critical displacement ahead of the crack tip under the mixed-mode condition is adopted as the fracture criterion based on the BCS crack theory. After the crack was bent, the subsequent fatigue crack propagated under the mode I behavior at the crack tip; therefore K_I determined from the discontinuous displacements could be regarded as ΔK_eff for the bent crack.

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Functionally gradient materials (FGMs) are advanced high-temperature materials capable of withstanding extreme temperature enviroments, and are produced by continuous change of two material components. In this work a FGM plate of PSZ and Ti-6Al-4V is suddenly heated and suddenly cooled on the ceramic surface side and is kept cool on the metal surface side. The transient thermal stress and the stress intensity factors are calculated by a finite-element method (FEM). Crack propagation from an edged crack on the surface of ceramics side and the optimum distribution of materials are shown and discussed from the calculated thermal stress and stress intensity factors.

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Strength evaluation of ceramic-metal joints, which had thin copper layers between ceramic materials and joint metals, and had interface cracks between ceramic materials and copper layers, was conducted based on interfacial fracture mechanics, considering plasticity of metals. A four point bending test of the ceramic-metal joints was also conducted. Estimated fracture load was compared with the experimental value. As a result, it was shown that linear interfacial fracture mechanics was applicable in strength evaluation of ceramic-metal joints with interface cracks, if thermal elastic plastic residual stress analysis was conducted to evaluate stress intensity factors corresponding to residual thermal stress. Fracture load estimated by thermal elastic-plastic analysis agreed fairly well with experimental value. Effectiveness of the σ_θmax criterion in strength evaluation of ceramic-metal joints considering plasticity of metals was confirmed. A good linearity of stress intensity factors extrapolation was obtained. Even in thermal elastic-plastic analysis, a good linearity was obtained in the range of r≥0.1a.

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Spall tests for three kinds of materials (A12024, SS41, Cu) are conducted using a newly developed testing device. This experimental assembly generates triangular stress waves with various gradients-in plate specimens (50×50×20mm) by direct explosive loadings. The relationship between measured spall layer thicknesses (5-15mm)and the explosive (PETN) thicknesses indicate that a time dependence exists in spall phenomena of the metals. A computer program with a cumulative damage model was constructed, which has reproduced the basic characteristics of the observed failure in the metals. It is known that the stress wave reflected at the free surface can be prevented from reaching the specimen plate by spallation of the momentum trap or spall plate, which is mounted in contact with the specimen. The following spall test results for A12024 have verified this effect and the numerical analysis also has simulated the phenomena successfully.

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The fracture mechanisms of FRPC (fiber-reinforced polycarbonate) molded using various screw shapes and numbers of screw rotations are investigated by the acoustic emission technique. The fracture mechanisms of the molded FRPC are considered from the viewpoint of the apparent shearing stress at the metering zone of the screw. It is found that the apparent shearing stress affects the fiber length and the fiber orientation of the molded specimen, and the loads representing the change in the damage mechanisms which are determined by the AE gradient method. The AE frequency analysis also reveals what damage mode occurs easily at the apparent shearing stress zone.

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The fracture mechanisms of fatigue-loaded fiber-reinforced polyethylene terephthalate (FRPET) composite with a notch are investigated by the acoustic emission (AE) technique and the residual strengths are estimated. It is found by AE frequency analysis that fiber breaking occurs at low stress amplitude but debonding between the fiber and the resin occurs as the stress amplitude increases. The residual strength can be estimated from the relationship between the ratio P/P_(N) of loads producing the change in the damage mechanism of the fatigue-loaded specimen and the non-fatigue-loaded specimen and the ratio N/N_f of the number of cycles N to the number of cycles to failure N_f.

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To verify and maintain the integrity of duplex stainless steels currently in service, we conducted a study aiming to develop a method to nondestructively estimate their Charpy-impact energy at room temperature. Hardness of the ferrite phase was found to be a reliable indicator of the process of embrittlement during long-term heating of duplex stainless steels, but further information on the ferrite phase and the austenite phase is required for the estimation of Charpy-impact energy. An equation involving the hardness values of the ferrite and austenite phases, the ferrite content and the average spacing of ferrite-phase islands was found to be applicable in the nondestructive estimation of Charpy-impact energy at room temperature.

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Nonlocal elastic constants associated with the higher-order strain gradients in the cosserat theory are linked to atomic-level properties, in particular, to coefficients that arise in lattice dynamics equations when atomic displacements are expressed in terms of a continuous displacement field. The key objective of this work is to describe elastic behavior on the mesoscopic scale. First the equation of motion (EOM) in the cosserat theory is derived in the most general form with the arguments of the deformation gradient tensor and its material derivative as well. Second the EOM in the lattice dynamics with the harmonic approximation is formulated by introducing the continuous atomic displacement field. Then the nonlocal elastic constants, including the ordinary fourth-order tensor, are expressed in terms of both the atomic positions in a relaxed (stable) configuration and the force constants which are the second derivative of the interatomic potential employed, with respect to position.

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The method for evaluation of Young's modulus through transient response was proposed in the previous paper. Although it approximated well for the case of a small temperature change, it did not for a highly nonlinear system with a large temperature change. The direct description method of temperature dependence of Young's modulus at prescribed points instead of a polynomial approximation method was applied to the evaluation method in order to improve the sensitivity of optimization variables to the objective function. It was found that the temperature dependence of a plastic material was well aproximated even for a highly nonlinear system. Increasing in the number of divisions improves the accuracy of the approximation, but at the same time degrades the convergency of the optimization. The optimum number of divisions was found to be in the renge of 5 to 7.

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A boundary integral equation method ( B. I. E. M.) for beam-columns on a Winkler elastic foundation is presented. The fundamental solutions required for the B. I. E. M. formulation are derived by solving the singular differential equations and are classified according to the magnitude of the tensile or compressive axial force. The formulation is verified by analyzing several sample problems and the results are compared with existing solutions.

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Homogenization formulae were developed for predicting the elastoplastic mechanical behavior of composite materials in a previous work. The nonlinear solution method for the finite element method makes it possible to compute the microscopic and the macroscopic deformations simultaneously, both of which reveal large deformations, and then accumulate the incremental solutions successively. The macroscopic deformation can be obtained by averaging the microscopic stress/strain state in each constituent, without a priori knowing an averaged stress-strain relation from experiments. Several numerical examples are presented to verify the formulation and to illustrate the three-dimensional nature in global-local simultaneous computation (G. -L. S. C.). The method is also applied to the analysis of interfacial damage of nonmetallic composite materials. The computational aspects of the nonlinear homogenization method are briefly discussed.

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Effects of the end-tab constraint on the off-axis tensile behavior of the carbon/epoxy unidirectional fiber composites were studied. We compared two end-tab shaps: the conventional rectangular end-tab and a new oblique end-tab proposed by Sun and Chung. For the specimens with the conventional rectangular end-tabs, the difference between the longitudinal and transverse strains at the center and near the end-tabs of the specimen becomes significant. For the oblique end-tab, such an inhomogeneity of the longitudinal and transverse strain distribution disappears in the linear elastic range. Also in the range of the subsequent nonlinear response, the oblique end-tab can significantly reduce the inhomogeneity of the strain distribution in the longitudinal and transverse directions of the specimens. Because of this reduced end-constraint due to the oblique end-tabs, the nonuniform Poisson's effect has been markedly improved. An undesirable effect of shear coupling on the measurement of the shear modulus was also reduced. Regarding the elastic modulus and the major Poisson's ratio measured at the center of specimens, however, no appreciable effect due to the different tab-shapes was found. The fracture stress has not been subjected to the effect of the tab shape difference.

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Inelastic and fracture behaviors of a new fiber-metal composite GLARE 2, a unidirectional hybrid laminate of glass/epoxy laminae and aluminum alloy sheets, have been examined under various off axis static tensile loading conditions. The classical laminated plate theory (CLT) has been applied to describe the off-axis inelastic behavior of GLARE 2, in which the failure-induced elastic degradation of GFRP plies was taken into account. For all off-axis angles, a clear transition from the linear to nonlinear deformation regime appears. The stress level of this sharp transition almost coincides with the yield stress of the constituent aluminum layers. The anisotropy in the fracture stress can be predicted using the Tsai-Hill theory. Taking into account the observation that for a 90°C off-axis specimen the tangent modulus in the nonlinear regime is almost in agreement with that of the monolithic aluminum alloy, we have considered transverse cracking in the GFRP plies and modified the CLT so as to include the instantaneous degradation of the transverse and shear elastic moduli due to the transverse fracture. The results obtained using the CLT with ply failure accurately described the characteristic behavior of GLARE 2.

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In this study, we examine a piezothermoelasticity in a two layered composite plate constructed of a piezoelectric plate and an isotropic plate when a stationary thermal load acts on a free surface of the isotropic plate. The coupling problem is analyzed by use of the potential function method. Numerical calculations for the stationary piezothermoelasticity are carried out for a bonded steel plate and a cadmium selenide plate, and the results are presented graphically in comparison with those derived from a single cadmium selenide plate.

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When an isotropic perfectly conducting solid cylinder is subjected suddenly to a uniform temperature rise in an axial magnetic field, a magnetothermoelastic stress wave occurs on the surface the instant the thermal impact is applied. The stress wave on the surface proceeds radially toward the center of the cylinder. The wave may accumulate at the center and give rise to very large stress magnitudes, even though the initial thermal stress is relatively small. This phenomenon is called the stress-focusing effect. This paper analyzes the effects of these waves precisely using the ray series. The results give clear indications of the mechanism of magnetothermoelastic stress-focusing effect in a perfectly conducting solid cylinder in an axial magnetic field.

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The mechanism of diffuse axonal injury (DAI) has been analyzed by means of computer simulations. A standard human model that reproduced the human head structure, and modified human models with some head substructures such as falx cerebri eliminated are constructed as finite element models. Rotational impacts are applied to the finite element models through the cranium. The bottom of the third ventricle is considered to be deemed the center of rotation. The rotational impact data of the standard human model evaluated from shear stresses such as von Mises stress show that those stresses are concentrated on the corpus callosum, thalamus and rostral brain stem located at the central region of the brain, which agrees very well with regions of DAI indicated by small hemorrhages found by clinical findings. The cause of the concentration of shear stress is investigated using the modified human models, and it is found that the high shear stress on periventricle such as the corpus callosum and thalamus is affected by the falx cerebri, while the high stress on the rostral brain stem is affected by the tentorium cerebelli. It is deduced that the mechanism of DAI is independent of the type of impact, and the shear stress is concentrated in the central region of the brain due to the effect of the head structure.

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In the previous report, a method is proposed to obtain the definitions for internal forces of continua, and then the balance equations for mass, force and moment are formulated using microscopic quantities. In the present paper, heat flux and internal energy are formulated and the energy equation is derived on the basis of lattice dynamics. In order to derive a definition of heat flux, a kinematical quantity of an atom is divided into macroscopic and thermal motion, and heat flux is defined using the thermal motion. Internal energy is defined as kinematical energy and potential energy of atoms in the mesodomain. These definitions of heat flux and internal energy are useful in obtaining macroscopic quantities from numerical solutions calculated by the molecular dynamics. The energy equation which includes heat flux and internal energy is expressed in terms of microscopic quantities.

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In this paper, effects of viscosity and aging on plastic deformation behavior of SUS316L stainless steel in tensile reloading and in relaxation after cyclic preloading, are investigated experimentally, and are analyzed theoretically based on the Two-Factors constitutive concept. Strain rate dependency of plastic flow stress decreases with an increase of number of cycle in precycling, this phenomenon is found not to be caused by viscosity change, but by an increase in aging effect. It is found that due to cyclic loading almost no change in viscosity property occurs for SUS316L stainless steel. The Two-Factors constitutive model is confirmed to give systematic predictions both on plastic flow behavior and on relaxation behavior of SUS316L stainless steel even after cyclic prestraining.

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Cavitation erosion of cast and sintered Ti-Al-based intermetallic compounds (Ti-48 Al and Ti 50 Al) was studied using a vibratory apparatus. The erosion resistance of intermetallic compounds is 20 to 70 times higher than that of pure titanium. Cavitation produces wavy undulations on the surface of intermetallic compounds. Microcracks are formed at the tip of the wavy undulations, where material removal occurs. The erosion resistance of sintered intermetallic compounds is slightly higher than that of cast compounds because of their smaller grain size. Ti-Al-based intermetallic compounds contain γ single phase and lamellar phase (γ phase and α₂ phase). The γ single phase is more work-hardened than the lamellar phase due to the accumulation of twinning deformations produced by the repeated action of cavitation bubble collapse pressures. Therefore, the erosion resistance increases with an increase in volume of the γ single phase, that is, the resistance of Ti-50 Al is higher than that of Ti-48 Al. It was concluded that the erosion resistance of intermetallic compounds can be evaluated in terms of HV²/E, where E is Young's modulus and HV is Vickers hardness after work-hardening due to cavitation.

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In order to ensure reliability of the thermoelectric module, we had applied a FGM layer with composition of Cu and Si₃N₄ to the bonding parts in the module and decided the functionally graded compositional profile based on numerical analysis. In this study, Cu/Si₃N₄ functionally gradient material and Cu/Si₃N₄ composite materials were fabricated by hot press (HP) and static strength at room temperature was evaluated. As a result, it was found by observation with an optical microscope that neither FGM nor the composite materials produced by HP had internal defects. Static strength of composite materials obtained by the 4-point bending test exhibited a lower value as compared with those based on the rule of linear mixture. Finite element analysis for the FGM was performed. It was shown that fractured stress and initiation site of cracks could be predicted by using the fracture criterion for the bending strength of the composite materials.

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Two kinds of GFRP under steady flexural load have been exposed outdoors since 1980. One of them is made of unsaturated polyester resin and chopped glass mat strands and the other is made of the same constituent materials but is covered with weatherable resin. In order to clarify the dependence of the weatherability strength on the exposure period, the four-point flexural test is used. The variations of flexural strengths, flexural moduli, fiber volume fractions and hydrolytic decomposition of polyester chains well fitted with Weibull distribution function. The relationships of these strengths to the exposure period and the effect of weatherable resin are reported in this paper. Furthermore, some cracks at the surface of specimens have been observed using an electron microscope.

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A multiple strata model for plasticity of polycrystalline metal based on the random barriers theory has been presented by compounding the activating state of slip systems with the moving dislocations. Applying the hardening characteristic of the slip system the moving dislocations can be allotted to each slip system depending on the magnitude of the resolved shear stress. The slips on the activating systems can be estimated according to the optional stress path with a model specimen consisting of many grains. The basic plastic constitutive equation of the random barriers theory has been reconstructed applying a new conversion tensor enabling connection of the actual macroscopic plastic strain with the ideal one by the slips. The validity of this model has been discussed in the light of the experimental results obtained from the proportional and nonproportional loading tests of pure copper.

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Necking phenomena, that is, diffuse necking and localized necking are associated with plastic instability. Diffuse necking was analyzed by Swift, who proposed the criterion that the loads in sheet plane become stationary simultaneously under plane stress. However, the loads obtained based on the criterion, in general, do not show the stationarity. In localized necking, the velocity gradient can become disontinuous on the necking plane. In the analyses by Hill and by Storen and Rice, the assumed mode of their necking plane does not satisfy normally the conformity for the discontinuous velocity gradient, and the volumetric strain is discontinuous across the necking plane. We proposed comprehensive criteria including modified diffuse and localized necking, deduced from the necessary condition for multiple solutions. However, it has not been examined whether or not the solution obtained is really multiple. The objective of this work is to perform this examination. Consequently, the sufficient condition for multiple solutions requires the nominal stress to be stationary, and the localized necking to have the defined two modes. They are satisfied in the intrinsic criterion of plastic instability.

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The adaptively shifted integration (ASI) technique is applied to the finite element analysis of dynamic collapse behaviors of impulsively loaded fully clamped beams and framed strcutures subjected to support excitation. The ASI technique is based on the equivalence conditions of standard beam elements and computational discontinuum mechanics models. Numerical integration points for evaluation of an element stiffness matrix are adaptively shifted to optimum positions, depending on the elastic or plastic state of the element. The highest computational efficiency and accuracy can be expected using the ASI technique for the finite element analysis of large-scale frames. The solutions given by the finite element methods with and without the ASI technique are compared to show the validity of the proposed technique.

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An autonomous distributed criterion to determine optimum postures of adaptive truss-type manipulators is suggested. A minimum compliance posture of variable geometry trusses for a given working load vector is realized by adjusting variable elements, where the adjusting values are determined independently according to the strain energy sensitivity of each truss part. The validity of the autonomous criterion is confirmed numerically by applying it to the configuration control of variable geometry truss containing ten adjustable elements.

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The authors proposed a new practical optimum design method that consists of two steps: the design of experiments and mathematical programming. The design of experiments is used to generate approximate evaluation functions for the controlling behavior depending on the changes in design variables of an object structure, by a series of finite element analyses (FEA). Based upon an orthogonal array of a combination of design variables, effects of the design variables can be calculated by a relatively small number of FEA, and then the approximate evaluation functions are generated by those effects based upon analysis of variance. The evaluation functions can also be used as direct tools for estimating the behavior of design structure. Finally, a successive quadratic programming (SQP) method is employed to solve the optimization problem of the approximate evaluation functions. It is confirmed that the proposed method can be used for almost all kinds of the nonlinear problems including the impact behavior of structures, and that it can be carried out in much smaller number of FEA than the other existing methods. As an example, the present method was used to solve an optimum design problem of an automobile seat frame subjected to impact loading. It was found that the present method is a very effective and powerful tool for the optimum design of various practical design problems.

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