The method of computational material testing based on damage mechanics, which was previously proposed by Toi and Hirose, has been extended to take into account the difference in damage effect on tensile and compressive material behaviors and in plastic damage evolution under monotonic and repeated loading. The proposed method has been identified for aluminum 6061-T 6 and steel for rails. The identified simulator has been applied to the low-cycle fatigue life prediction of aluminum under repeated tension/compression as well as a steel beam under repeated three-point bending by the locally coupled approach using the three-dimensional finite element structural analysis and the proposed computational material testing. The validity of the present method for computational fatigue life prediction has been demonstrated by the comparison of calculated results and corresponding experimental results.

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Electronic states of single wall carbon nanotubes (SWNTs) under uniaxial deformation are analyzed using the tight-binding and first principle calculations. It is known as a curious and applicable phenomenon that the band gap drastically changes according to chiral vector which characterizes the geometric property of the SWNT. There are a few studies that have treated coupled behavior between mechanical and electronic properties. Most of the previous works have been determined the deformed atomistic structure by an empirical potential and then performed band analyses. This step-by-step process may have a possibility of making an error due to lack of transferability of the empirical potential at highly deformed state. In this study, in order to estimate electronic structure change more accurately, we used a tight-binding representation parameterized by Wang and et al. to relax the atomistic structure and estimate band gap simultaneously. We also performed more reliable first principle density functional calculations for the same models and estimated reliability of the tight-binding method.

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In this paper, in order to create the functional continuum for the nonlinear problems, the design method of arranging slits to a simple continuum is proposed. The dynamical effects of slit arrangement are estimated by the FEM analysis of the fundamental models of the plate and cantilever. From the analytical results, it becomes clear to obtain the displacement reduction effect and the nonlinear displacement response according to the condition of slit arrangement. This method is applied to two practical problems. On the first problem, it is shown by the optimum design of the slit arrangement to a square plate that the functional continuum as a precision positioning X-Y stage can be designed.On the second problem, it is shown by the experiment that the cylinder which arranges two slits has the availability as a cam outputing a nonlinear displacement response.

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Different behaviors between the edge and screw dislocations in the γ/γ'microstructure of Ni-based superalloy are investigated by using molecular dynamics simulations. The simulations are implemented with a slab cell of Ni matrix involving an apex of a cuboidal Ni3A1 precipitate, that mimics a part of the idealized γ/γ' microstructure with about 3 million atoms. Mode II and III type displacements are applied on the cell to nucleate the edge and screw dislocations, respectively, and proceed them toward the precipitate. The edge dislocation decreases its velocity at the γ' precipitate, showing dislocation pinning there, then penetrates it under the force from the follow-on dislocation.The screw dislocation runs through the precipitate without slowdown by shrinking the with between its Shockley partials. Detail investigation of the stress distribution suggests that the constriction is due to interactions between the stress field around the precipitate and the partials : the stress causes repulsive Peach-Koehler force on the leading partial and attractive on the trailing since their edge components have opposite Burgers vectors. In addition to the fact that the strain energy of a screw dislocation is smaller than that of an edge, the constricted screw dislocation makes smaller atomic step on the γ' precipitate than the extended edge dislocation. Thus the screw dislocation easily penetrates the precipitate while the edge is pinned.

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Two molecular dynamics simulations are conducted on the deformation behavior of the crystal/amorphous interface of polyehylene under tension. One, Model 0°, has the crystal of which chain direction is parallel to the tensile axis. The other, Mode1 45°, has the chain direction rotated 45° against the tensile direction. Detail observation of the chain structure at the interface in the equilibrium state unloaded, reveals that the interface in Model 45° is serrated by the recrystallization of amorphous chains while Model 0° has no remarkable change in the morphology of the interface.It is also observed in both Model 0° and Model 45° that the comformational defects propagate in the chain direction and make disorders in the crystalline phase. Then the tensile strain is applied on the models, leading the following results : (a) Model 0° shows the yielding and strain hardening, as observed in the nanoscopic specimen without crystalline phase reported in our previous work. The same mechanism of chain orientation and elongation take place in the amorphous phase at the interface. (b) Model 45° exhibits linear stress increase from the begining of the straining without remarkable yielding. It is because the molecular chains in the crystalline phase is also subjected to the force normal to the chain direction, so that the crystal deforms in the non-bonded direction and shows stress increase.

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The new material fender that was made with TPE (Thermo Plastic Elastomer) is excellent in restoration, and it has good compression characteristic for energy absorber. We are doing the research that checks the characteristic of the new material fender for ship collision by the model test and numerical analysis. This report studied the characteristic of the new material fender for ship's head-on collision by using the PEL-fender and urethane foam as the model. When rearranging the results, (1) When the entrance angle of the bow becomes large, the slope of a reaction force-bow penetration curve becomes steep. At this time, the change rate of the slope becomes steep with the increase of the entrance angle. Although reaction force differs as for PEL-fender and urethane foam, these trends resemble. (2) The reaction force of the dynamic test is bigger than the reaction force of the static test. (3) Absorbing effciency and energy absorbing factor do not change by the bow measure.

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A cultured endothelial cell on a substrate was modeled as a homogeneous, incompressible, isotropic, hyperelastic structure consisting of the cell cytoplasm and nucleus and the substrate. Finite element analyses were used to evaluate the stress/strain distributions in the cell when stretch was applied to the substrate. The results reproduced experimental results reported in the literature. The strain component in the stretch direction decreased as the position in the cell became higher. The rate of decrease in the strain with height depended on the shape of the cell. This means that the cellular dimensions are required to evaluate the measured cellular deformation adequately. The analysis also showed that our model had a region with the same decrease in strain as that reported in the literature. We could also predict the orientation of stress fibers by using the deformation data obtained from the finite element analysis of the cell.

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The present paper discusses an approximate optimization method using the neural network in order to design a multi-layered composite plate constructed of an isotropic structural layer and multiple piezoceramic layers of class 6mm. The puropse of this design is to determine the ticknesses of the piezoceramic layers, such that the maximum value of the electric potential distribution which controls the thermal displacement on the surface of the structural layer is minimized subject to stress constraints. Instead of the back propagation method, the quasi-Newton method is employed for an updating formula of the connection weights. By restricting the normalization range of the training data, total execution time necessary to the training process are remarkably reduced. Thus, performance of the learning algorithm is greatly improved. Applying the improved learning algorithm to the design of the multi-layered composite plate, fairly good results for the approximate optimization are obtained.

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A new hybrid method is proposed to estimate the spalling stress normal to the interface in thermal barrier coating. As the X-ray energy becomes higher, the penetration depth gets deeper. The in-plane stress, σ₁, is measured by the conventional X-ray with the low energy, and the out-of-plane stress, σ₁-σ₃, is measured by the synchrotron X-ray with high energy. The spalling stress, σ₃, can be estimated from two measurements obtained by the conventional and the synchrotron X-ray methods. The bond coating of NiCoCrAlY with a thickness of 0.2 mm was made by plasma spraying on a Ni super-alloy substrate, and the Zr0₂ top coating with a thickness of 0.2 mm was plasma sprayed on the bond coating. The distribution of the in-plane residual stresses, al, in the top coating was measured with characteristic X-rays Cr-K_α by repeating the measurements after successive removal of the surface layer. The residual stresses, σ₁-σ₃, were measured by the synchrotron X-rays with 73 keV. The spalling stress was estimated from the stresses measured by the two methods. The spalling stress, σ₃, was small tensile beneath the surface of the top coat but increased to 75 MPa near the interface between the top and bond coatings. A high tensile stress near the interface may induce the delamination of coatings.

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The differential equation for the macroscopic total strain of a material with respect to the crack density of the crack is derived by adopting the concept of the differential scheme when a infinitesimally small amount of slit-like crack is introduced to the matrix of the material containing many aligned slit-like cracks. By solving this differential equation, the macroscopic total strain, the average interaction stress and hence the macroscopic elastic moduli are formulated as a function of the crack density of the crack. On the contrary to the results obtained by the ordinary Mori-Tanaka thorem, the resulting macroscopic elastic moduli asymptotically tend to zero as the crack density of the crack increases. The present results have the same degree of accuracy with the self-consistent method and are good agreement with the numerical results given by Huang et al (8). especially at relatively low crack density. The volume fraction of the aligned slit-like cracks in physical meaning is obtained by comparing the resulting interaction stress with that derived from the Mori-Tanaka theorem.

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In this paper, we investigate the steady state thermal stresses in an elastic thick plate containing an oblate spheroidal inhomogeneity, when the circle regions of radius d of the upper surface is heated and the one of lower surface is cooled. The solution is deduced with using thermoelastic displacement potential and Papkovich-Neuber displacement potentials. Numerical results are presented for different heat areas, inclusion shapes and sizes, and the stress distributions in the vicinity of the inhomogeneity are illustrated graphically.

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One-sided fastening systems using plastic buckling of the thin-walled pipes with flange are studied in this paper. Plastic buckling occurs in the thin-walled pipe area of the blind nut with flange, when an axial compressive load is applied to the blind nut. As one-sided fastening is applied for the case such as the inner hollow part, estimations of buckling load and the proper displacement are important. The buckling deformation is studied by the nonlinear finite element analysis, and the numerical results are in good agreement with experimental observations for the buckling load and displacement. Effects of geometrical parameters of the thin pipe area are investigated for the buckling load and displacement by FEM. In order to evaluate the tensile strength of the fastening systems, unloading and reloading is carried out consistently by analyses. Effects of the tensile strength with the length and thickness of the thin-walled pipe area of the blind nut are also investigated

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For maintenance of the back-up roll used in iron and steel rolling, it is important to establish evaluation technique for the rolling contact fatigue damage. Thus far, progress of fatigued zone below the surface of rolls has been evaluated using profile analysis of half value breadth of X-ray diffraction line. However, the development of quantitative evaluation of the rolling contact fatigue damage is moreover expected. Therefore, in this study, we estimated the density of movable dislocation under the rolling contact fatigue process by measuring ultrasonic surface wave velocities with three-different propagating frequencies via Granato-Lücke's dislocation string theory. The comparison of changes of the loop density of movable dislocation with changes of half value breadth of X-ray diffraction line profile analysis under the rolling contact fatigue process suggests promising availability of the proposed method. As a result, the ultrasonic surface wave velocities with three-different propagating frequencies (5, 10 and 14 MHz) decrease due to increase of the rolling number of rolling contact fatigue. And, the loop density of movable dislocation estimated by Granato-Lücke model increases as the fatigue damage progresses.

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It is considered that the rate dependence of the flow stress of metal materials is caused by both viscoplasticity and dynamic aging. In this study, influence of temperature on viscosity and dynamic aging which dominate plastic deformation behavior of SUS316L/316 stainless steels after cyclic preloading is investigated experimentally, and is analyzed theoretically based on the proposed elasto-viscoplastic constitutive model with effect of dynamic strain aging. It is found that, at about -35°C to 150°C, viscosity shows very small change even after cyclic loading. On the other hand, aging shows great increase due to cyclic loading and both viscosity and aging decrease with an increase in temperature for SUS316. Aging is very small and increases slightly with increasing of temperature for SUS316L. The proposed elasto-viscoplastic constitutive model used in this paper is confirmed to give systematic predictions of rate dependent stress-strain relations of both SUS316L and SUS316S.S. at the temperature of about -35 to 150°C.

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In order to measure cyclic biaxial stresses by an electrodeposited copper foil with microcircular holes, both occurrence rate of slip bands at the periphery of microcircular holes and the grown grain occurrence rate in copper foil itself have been used. However, this method needs a great many microcircular holes to obtain high accuracy. So, in this report the different method from that ever used is examined. Namely, as the biaxial stress ratio affects the stress distribution of the periphery of circular hole in a plate, it is also expected that the distributed shape of grown grains at the periphery of circular hole in a copper foil is different with biaxial stress ratio. From this viewpoint, the length of the circumferential direction and radial direction of grown grains appeared are measured under various biaxial stresses, and the basic equations are proposed to obtain principal stress.

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