Carbon nanotubes (CNTs) have been attracting attention because of their prominent mechanical and electronic properties. In this study, we investigate the deformation of single-walled carbon nanotubes (SWCNTs) with a bend junction using molecular dynamics in order to analyze strain concentration due to the tube shape (macroscopic effect) and the membered ring shape (microscopic effect). At first, we propose a method for evaluating the local strain at each memberded ring. Then, we analyze the strain concentration at the bend junction due to the both of macroscopic and microscopic effects. The strain concentration caused by the microscopic effect is separated by a rough analysis ; and it is about 1.5 times higher than that caused by the macroscopic effect.
Efficient interatomic potentials for Pb (Zr, Ti) O3 (PZT) crystals, which are intensively applied to ferroelectric devices, are required for the atomic-scale study of the mechanical and electronic behavior of the materials with the increasing demand of further improvement of the devices. In this study, we develop parameters of empirical shell-model potential functions, with which large-scale atomic simulations will be feasible, for the equilibrium lattice parameters and atomic displacements of ferroelectric state and the elastic constants of tetragonal PbTiO3, PbZrO3 and PbZr0.5 Ti0.5O3 based on first principles calculations. The potentials individually optimized for PbTiO3, PbZrO3 and PbZr0.5 Ti0.5O3, respectively, reproduce both the structures and the elastic constants of each crystal in good accuracy. The potential simulataneously fitted for all the crystals yields the structural parameters successfully, whereas some components of the elastic constants are poorly reproduced.
The structural changes with volume expansion in low-temperature (a) phases of quartz and cristobalite, the typical polymorphs of silicon dioxide (SiO2), have been studied through first-principles calculations using the projector-augmented-wave (PAW) method, with particular emphasis on their negative Poisson's ratio behavior. The dominant mechanism of expansion is the increase of the Si-O-Si angles within their crystalline structures, whereas the SiO4 tetrahedron undergoes only a slight distortion. We provide theoretical ab initio results for a complete set of independent elastic constants of quartz and cristobalite with volume expansion. For comparison, the adiabatic elastic constants of both polymorphs are evaluated at finite temperatures, using the molecular-dynamics simulations with a nonempirical pairwise potential. Our calculated elastic properties are found to be in good agreement with the experimental data.
An efficient boundary element method is proposed for three-dimensional corrosion analysis of structures having net geometory, such as rebars in a reinforced concrete structure and a guard fence for a sea-side structure. The proposed method is based on the Fourier series expansion of boundary quantities, i.e., potential and current density, in the circumferential and axial directions of a net structure. It is possible for the new method to reduce largely an enormous number of elements which would be necessary in the conventional method to discretize the structures having net geometory. In order to demonstrate the usefulness of the proposed method, a couple of example problems of rebars in a concrete structure with a cathodic protection system are presented.
The finite element method has been used in impact fracture analysis. But, enormous labor is necessary for the mesh generation. When we analyze the large deformation and dynamic fracture, there are cases in which the remesh process is very difficult. Recently, it began to use the meshless analysis methods such as the Distinct Element Method and Smoothed Particle Hydrodynamics for the analysis of the impact phenomenon. In this research, we extended the two-dimensional Extended Distinct Element Method (EDEM) to the three-dimensional EDEM. To verify validity of the three-dimensional EDEM, we analyzed impact fracture when a small sphere collided with the ceramic tile at very high speed and when a plaster cylinder fell freely in the floor. From numerical results, we confirmed that the behavior of impact fracture can be analyzed in detail by the three-dimensional EDEM.
In order to reduce the development for the electric device productions, the numerical analysis has been applied well. However, a seamless numerical technique is also required for design, because the modem productions are consist of many components with different size. The multi-scale analysis has been applied to the seamless numerical technique fo these productions. But, the traditional two-scale technique can't adopt, because the differences of size between comportments are very lange. Therefore, M3 method with three-scale technique has been proposed to satisfy the requirements on 1st paper. In this paper, the formulation and a typical example of thermal analysis have been described. Especially, a heat transfer problem under an unsteady state has been analyzed by M3 method and the traditional FEM with fine mesh. A composite material with a particle in the matrix has been treated as a typical example. The numerical results obtained by M3 method have good agreement with the numerical ones obtained by the traditional FEM with fine mesh. It is demonstrated that the distinctions of the rise in temperature and the thermal flow front are generated by the local heterogeneity. In addition, it is revealed that the operation time of mesh generation can reduce dramatically because three scale meshes can generate with the individual operations. From these results, it is recognized that we can reduce the period of the development because M3 method can apply the structure with different size comportments.
Microstructure formation and the stress evolution in the microstructure is simulated based on the coupling equations among the phase, temperature and stress/strain. Grain growth processes from some nuclei of the precipitated phase are simulated under three different conditions. Assuming volumetric dilatation in transformation to the precipitated phase, tensile and compressive stresses are generated at the interfacial region, and the distribution changes as the grain grows. The elasto-plastic model gives the residual stress distribution in the material, which is not able to be obtained by the elastic calculation. A grain-growth model with regularly disposed four nuclei demonstrates creation of residual stress zone along the grain boundaries. Another model with randomly distributed nuclei also gives the residual stress distribution along the grain boundaries, in which dependence of the stress on the size and shape are observed.
In this paper, discussions on B-spline wavelet Galerkin method are presented for its mathematical formulations and numerical implementations. Scaling function and wavelet are used as the trial and the test functions in Galerkin formulation. These basis functions have the so called multiresolution property. B-spline scaling function and wavelet have simple forms and are easy to integrate and differentiate. However, there are some difficulties in dealing with external boundaries. They are due to the loss of linear independence of the basis functions. To circumvent these problems, we introduce the boundary scaling functions/wavelets or eliminate particular basis functions that can be expressed by the linear superposition of the other basis functions. Numerical results are presented for the problems of tensile plate with a circular hole.
In this paper, elastoplastic crushing behavior of circular tubes under axial compressive loading is studied by using nonlinear finite element analysis software MSC.Marc. In particular, effects of strain hardening on the average crushing load P ave in axial collapse are investigated. It is found that the average load P ave depends on the scale of strain-hardening, and the theoretical result of P ave for rigid perfectly plastic material cannot be used to evaluate the load P ave with strain-hardening material. So in order to take into consideration the strain hardening effect on the average load P ave, we propose an energy equivalent flow stress σ flow defined by the value of average effective plastic strain ε p, eq which arises in one folded wrinkle, and evaluate the average load P ave by using σ flow instead of yield stress σ y. This approximate evaluation agrees well with the experimental result.
In the prediction of deformation behaviour of soil, it is important to specify the inherent properties of the soil itself, although it is needless to say that appropriate constitutive equations must be applied in its analytical treatment. As the inherent properties there are the shape of yield curve and hardening characteristics. The yield curve represents the relation between the hydrostatic pressure and the equivalent deviatoric stress in the process of plastic deformation. On the other hand, the hardening characteristics correspond to the yield curve expansion accompanying with plastic deformation. These inherent properties are independent of the loading manner to be assigned to the soil. In this paper, the yield curve and the hardening characteristics are specified referring to the deformation behaviours on one of loading paths. Then, they are applied to the prediction of deformation behaviour on the other loading paths. In the results obtained, the difference of behaviours could be shown reasonably between loading paths, but they were numerically imperfect in comparison with the experimental observation. However, the method makes it possible to predict the plastic behaviour on the basis of the material characteristics referred.
Recently, development of medical devices such as catheter and stent are advanced in the low invasion medical field. Considering the functions of human body are affected severely by the medical devices, the high strength reliability of devices must be secured. In these circumstances, the thin metal film, which has high reliability of strength, is useful structural material for further development of low invasion medical device. As the strength characteristics of a thin film depend on thickness and formation process of itself, there is little strength database concerning a thin metal film. In this study, a tensile fatigue testing apparatus with cyclic loading frequency up to 30 Hz and maximum loading 8 N for the thin metal film has been developed, and thin rolled films Ti and SUS304 were evaluated on tensile and load-controlled fatigue strength. The static tensile tests give that both are also over the twice of the bulk material on the tensile strength, and the proof stress is high-strength with over 90% of tensile strength respectively. The fatigue test shows that Ti thin film has long life in comparison with the bulk material, however, the fatigue characteristic itself is similar like that of bulk material.
Fatigue behavior of metallic materials in very high cycle regime has become an impotant subject to guarantee the safety of mechanical structures during the long term service. In order to perform fatigue tests in very high cycle regime of N=109, a long period such as 230 days is required at the testing fiequency of 50 Hz. The multi-type fatigue testing machine which can give cyclic loadings to a number of specimens simultaneously is valuable to obtain fatigue test data within the specified period. From this point of view, a multi-type fatigue testing machine for axial loading was developed by using a special hydraulic system with a rotary valve to distribute high pressure oil into the respective actuators. By means of this testing machine, fatigue tests for four different specimens can be perfermed simultaneously at the frequency of 80 Hz. The loading capacity for each specimen is ±10kN and the applied load can be given independently to the individual specimen. Thus. one can perform the fatigue tests in the long life regime for many specimens within the specified period even in the usual frequency where the temperature rise does not take place on the specimens. The fundamental structure and its performance are presented here together with the fundamental experimental results on the bearing steel of SUJ 2.
Young's modulus (E) and tensile strength (S) of sintered steels depend mainly on porosity (P).The relations of P to E and S are described as E= (E0-Esub) exp (-bE·P) +Esub and S= (S0-Ssub) exp (-bs·P) +Ssub, respectively, where E0 and S0 mean the mechanical properties at P=0, Esub, bE, Ssub, and bs are experimental constants. The Esub and bE are affected by pore characteristic, such as pore shape, size, and interconnection, and S0, Ssub, and bs depend on not only the pore characteristic but also metal matrix structure. The fitting curves of shear modulus and 0.2% proof stress used by the above relation of P also correspond to the measured values of them, respectively. And then, Poisson's ratio calculated by the above relatons of Young's and shear moduli correspond to the measured value in comparison with Poisson's ratio calculated by the fitting equation, the type of E=E0 exp (-bE·P), of each modulus. Furthermore, the relationship between ln (S-Ssub) and ln (E-Esub) of sintered steels shows the positive linear correlation.
In certain materials, the yield point appears clearly ; in other materials, it is indistinct. Using an intelligent universal test machine, the yield point is measurable even in materials with an indistinguishable yield point. The test machine used in this study can measure stress, strain and time simultaneously. Heretofore, the boundary of plasticity and elasticity has been denoted as the elasticity-plasticity transition point (E-P point σep) to distinguish it from the yield point. In this study, the behavior of the E-P point σep of an indistinguishable-yield-point material S45C material is analyzed on the basis of the change in of the elevated tensile speed V1 increase. Experimental results were analyzed on the basis of the relationship between stress and strain due to elastic recovery (reducibility strain), and between stress and stress due to elastic recovery (reducibility stress). In this paper, we explain that the E-P point σep of S45C material in accordance with tension is based on the elastic recovery of S45C material.
Aluminum alloy has been used in several kinds of industries against a background of environmental problem and energy saving because aluminum alloy has a lot of advantages ; lightness, recyclability and good corrosion resistance. However, aluminum alloy has poor wear-resistance, so in order to solve this problem, DLC (Diamond Like Carbon) coating which indicates high tribological properties was performed. However, there are some reports which are concerned that coated materials like DLC indicate low fatigue strength compared with substrate only due to high heating history during the coating process. So, in this study, in order to improve wear resistance and to prevent the base material from decrease of fatigue strength, original DLC coating was suggested ; (i) coating process was performed by using UBMS (Unbalanced Magnetron Sputtering) method, and (ii) inter-layer which was doped Tungsten was formed on the substrate, and on the inter-layer (iii) two kind of DLC coatings were laminated for nano order. Wear tests and fatigue tests were carried out. Aluminum alloy coated DLC indicated very low wear rates, excellent tribological properties. Furthermore, it indicated high fatigue strength compared with substrate only.
Fatigue crack propagation tests of PZT specimens were performed under cyclic four-point bending with and without superposition of electric fields. The specimens were poled in the longitudinal direction (PL specimens) perpendicular to the crack plane. The crack propagation rate for the case of open circuit was faster than that for the case of short circuit. The application of a negative or positive electric field parallel to the poling direction accelerated the crack propagation rate, and the amount of acceleration was larger for the case of the negative field. The change of the crack propagation rate with crack extension can be divided into three regions. In the region I, the crack propagation rate decreases with increasing crack length, and then turn to increase in the region III. In the region II, the propagation rate is nearly constant. The mechanisms of fatigue crack propagation were correlated to domain switching near the crack tip. The grain boundary fracture was predominant in the low-rate region, while transgranular fracture became abundant on the unstable fracture surface.
Recently, there are a lot of thing to make the recyclable resource as a raw material in various fields. The reason for the earth resource is that there is a limit. The recyclable resource is used as for two-cycle engine for a small output. The cylinder is undertaken to the high temperature and the high pressure while the engine is working. As a result, the thermal deformation occurs in the cylinder. The bubble might come to be mixed when the crack occurs in the cylinder for the aged deterioration and while the engine is casting. The stress concentration is caused at the edge of this crack, and it becomes of one of the reason for destruction when the crack progresses. There is a method that evaluates from the viewpoint of the destructive power study to the stress intensity factor to see the stress change by the position of the crack and the bubble from thinning the thickness of the cylinder wall to lighten it. The deformation of the cylinder was measured and the behavior of the cylinder was simulated by the FEM method. This research is the evaluation of the stress change seen by the crack because of the deformation of the cylinder and the position of the bubble by the photoelasicity method and the caustics method.
The general solutions for a penny-shaped crack in an infinite solid, subjected to arbitrary tractions on the crack surfaces were derived. The applicability was demonstrated deriving the closed-form solutions for a penny-shaped crack subjected to the lower-order loading such as constant tension, shear, bending, and torsion. Furthermore, we consider a circular crack subjected to cubic-order normal stresses. It is shown that the stress intensity factor distribution derived from the general solution exactly agree with the analytical solutions derived by Shah-Kobayashi.
Slip deformation in compatible-type tri-crystal models subjected to tensile load is investigated by using a continuum-mechanics-based crystal plasticity analysis technique. Accumulation of geometrically necessary dislocations (GDNs) and statistically stored dislocations (SSDs) are studied in detail. Mutual constraint of grains through the grain boundary plane does not occur in the compatible type tri-crystals, but results of the analysis show non-uniform deformaion and high density of GNDs accumulated in the form of band in each grain. Mechanism of non-uniform deformation and accumulation of GNDs in the form of band in the compatible-type tri-crystals is discussed from the viewpoint of multi-body interaction between constituent crystal grains. The multi-body interaction is shown to be caused by shape change of grains after slip deformation and contribute for the formation of disclination type displacement field at the grain boundary triple junction.
We propose a generation laser scanning method for imaging of propagation of ultrasounds. Scanning a pulsed laser beam on an object for the generation of ultrasounds, the propagated ultrasounds were detected by a fixed PZT transducer. Although detected waves were ultrasounds generated from the different irradiation points, we could, by means of simple data processing using the measured waveform data, produce the animation images of the ultrasound generating from the reception transducer position. Because this method requires no adjustment of beam incident angle and beam focus, we can easily visualize the ultrasound on a solid media having any complicated shape. The distinguishing features of this method are applicable even in a field inspection work.
In this paper, a method to measure the guided wave using piezoelectric film is described. Since the guided wave is expected as the most promising technique for rapid long-range inspection of pipe, several articles have been devoted. It is thought that the piezoelectric film is suited to the measurement of the guided wave for its excellent sensitivity and other good properties. First, in this paper the relationship between the strain and output current of the film is deduced. It is shown that the output current depends on the angle between the elongation direction of a film and the radial direction of a pipe. It is also shown that the output current depends on the normal strain or the shearing strain by the use of laminated piezoelectric films. Then, experiments of measuring the guided wave are performed and the validity of deduction is confirmed.
This study was performed as a part of the research on the ultrasonic measurement in vivo of bone porosity, density, Young modulus and hardness. It was clarified that the bone porosity estimated by Biot's theory agrees well with the actual porosity within an accuracy of 5%. In the estimation the structure factor involved in the Biot's theory was determined as a value of 2. In this evaluation, an use of the propagation velocity of the fast wave is more advantageous to estimate the bone porosity than using the one of the slow wave. The estimated bone density by Biot's theory yields only ±5% differences from the measured value by the Archimedes method. Therefore, bone density can be estimated precisely by using the proposed ultrasonic wave method.