An optimization calculation is demonstrated that uses a new parameter U* which indicates load paths in structures. The optimized structure that realizes the most efficient load paths is compared with the conventional optimized structure that has the highest strength and stiffness. The two optimized structures for a simple rectangular plate have almost the same thickness distributions. While the present method optimizes only the load paths and does not intentionally produce structures having high strength or stiffness, it is notable that the structure obtained using the present load path optimization exhibits high strength and stiffness.

抄録全体を表示

This paper describes a newly developed optimization system for mechanical structures with coupled problems concerning heat conduction and stress analysis, which is based on the new Finite Element Sensitivity Analysis (FESA). In this system, the variation of material properties, for example heat conductivity, is considered as structural changes because it is difficult to change the material properties locally or partially. As well as the FESA, this system requires just one calculation and then brings the efficient designing products. The effectiveness of the system was verified by results showing that optimizations for structural design were given efficiently when the system was applied to the design of actual industry products, a turbine blade and a cooling jacket of computer modules.

抄録全体を表示

In general, internal cells are required to solve elastic problems with gravity load in non-homogeneous materials using a conventional boundary element method (BEM). However, in this case, the merit of BEM, which is ease of data preparation, is lost. In this study, it is shown that axial symmetric elastic problems with gravity load in non-homogeneous materials can be solved without the use of internal cells, using the triple-reciprocity BEM. A body force distribution is interpolated using boundary integral equations. A new computer program was developed and applied to solving several problems.

抄録全体を表示

The effect of hydrogen on the metals is known as hydrogen embrittlement, which affects the structural integrity of a hydrogen energy system. Hydrogen atoms near a crack tip play an important role in the hydrogen embrittlement. In the present paper, we developed a computer program for an transient hydrogen diffusion-elastoplastic coupling analysis by combining an in-house finite element program for hydrogen diffusion analysis with a general purpose finite element computer program for stress analysis. In the hydrogen diffusion equation, we consider both the hydrogen concentration at the normal interstitial lattice sites and that at the trap sites, and also take account of hydrogen diffusion flux due to hydrostatic stress. We use a hypothesis that the hydrogen absorbed in the metal affects the yield stress of the metal. Therefore, the hydrogen diffusion problem is coupled with the elastoplastic stress problem. Using the computer program developed in the present study, we performed the transient hydrogen diffusion-elastoplastic coupling analysis of a cracked plate made of a bcc-metal, and obtained the hydrogen concentration, hydrostatic stress and plastic strain near the crack tip. In the present paper, we discuss the effects of the initial hydrogen concentration, the boundary condition of hydrogen on the free surface and the loading frequency. An important finding obtained from the present study is the fact that the hydrogen concentration near the crack tip depends greatly on the loading frequency. The fact indicates that the fatigue lives of the components in a hydrogen system depend not only on the number of loading cycles but also on the loading time.

抄録全体を表示

A numerical method using the path independent H-integral based on the Betti reciprocal principle was developed to analyze the stress intensity factors of an interfacial corner between anisotropic bimaterials under thermal stress. According to the theory of linear elasticity, asymptotic stress near the tip of a sharp interfacial corner is generally singular as a result of a mismatch of elastic constants. The singular order and the eigenfunctions are obtained using the Williams eigenfunction method, which depends on material properties and the geometry of an interfacial corner. The singular order is real, complex or power-logarithmic. The amplitudes of the singular stress terms can be calculated using the H-integral. The stress and displacement around an interfacial corner for the H-integral are obtained by the finite element analysis. A new definition of the stress intensity factors of an interfacial corner that is proposed involves a smooth expansion of the stress intensity factors of an interfacial crack between dissimilar materials. Asymptotic solutions of stress and displacement around an interfacial corner are uniquely obtained using these stress intensity factors.

抄録全体を表示

In this paper, the collapse behavior of a thin-plate subjected to axial compression is studied by using the finite element method. It is revealed that the collapse of plate is induced by two dominant factors. First factor is the limitation of the stress of material, and second one is the limitation of in-plane deformation at the side edge of plate. Then, the judgment method, which becomes a dominant factor either the limitation of the stress or the in-plane deformation, is found by using the critical plastic strain. Further, an approximation prediction method of the collapse stress for the collapse mode of in-plane deformation is proposed, and its validity is verified comparing with the numerical results by FEM under various conditions, such as material property, geometric and boundary conditions.

抄録全体を表示

An optimization problem of both-ends-clamped beam which is subjected to a concentrated load is considered. It had been shown in the previous report that the actual most suitable form within the same volume exists only under a certain specific condition that a load was in a limited central region of the span. In this paper, an iterative method that uses numerical integration is adopted. Through the comparison with the analytical solution, the characteristic of the optimum solution is discussed. It is found that there exist solutions in which the deflection angle is discontinuous at the hinge points.

抄録全体を表示

SH transient problem for the elastic half-space including a micro plane crack is considered. If there is no crack we can exactly analyze this problem with application of the Cagniard method. Even if there is a crack we can correctly estimate the stress response at the crack position on the arrival time of wave-front incoming to the crack. The calculated stress value at the crack position is newly defined as the stress boundary condition. The transient reflection response spreading outward from the crack can be analyzed by using the Wiener-Hopf technique. The reflection region from the crack is shifted by the parallel translation and the rotation of the coordinate, and is superimposed on the no crack response region. Finally, for stress, strain energy and displacement, the transient responses are calculated for all wave field and shown in the form of the contour mapping representation.

抄録全体を表示

The influence of chemically-induced expansion on the fracture damage of a ceria based solid oxide fuel cell (SOFC) was investigated by using numerical stress analyses. The single cell examined in this study was composed of electrolyte [(CeO₂) _0.8 (SmO_1.5) _0.2], anode (Cermets of NiO-20 SDC), and cathode (La_0.6Sr_0.4Co_0.2Fe_0.8O₃), respectively. The finite element method was employed to calculate the residual stress, thermal stresses, and chemically-induced expansion stresses for the single cell. The residual and thermal stresses were calculated much smaller than the fracture strength of the individual components of the single cell. On the other hand, the chemically-induced expansion stresses were shown to remarkably increase for the temperature range greater than 973 K and accounted their magnitude for the primary part of the induced stress. It was shown from the stress analysis that the maximum stress induced in the single cell exceeded the fracture strength of the individual components at the onset of the fracture damage detect by acoustic emission method. The above-mentioned calculation results suggest that the chemically-induced expansion should be taken into account for the use of ceria based ceramics materials in SOFCs.

抄録全体を表示

Creep rupture behavior of a unidirectional carbon/epoxy T800H/Epoxy Laminate under constant off-axis loading conditions at different temperatures of 60, 100 and 130°C is examined. Tensile creep rupture tests are performed on plain coupon specimens with different fiber orientations θ=0, 10, 30, 45 and 90°. Creep rupture of specimens takes place predominantly along reinforcing fibers is a brittle manner, regardless of the fiber orientation. The log-log plots of the creep rupture data can approximately be described using straight lines with negative slopes over the range of rupture time up to 10h, regardless of the fiber orientation. Then, two kinds of simple phenomenological models are developed for predicting the time-to-failure of unidirectional composites. Validities of those models are evaluated by comparing with experimental results. It is demonstrated that the proposed models succeed in adequately predicting the creep rupture lives of the unidirectional composite at different temperatures.

抄録全体を表示

Hot pressing of bamboo (Phyllostachys pubescens) fibers that were obtained by using steam explosion was carried out under various molding conditions such as temperature and pressure. In this paper, the effects of the molding conditions on the bulk density, tensile strength, and bending strength are discussed. Further, the effect of the heating temperature on the strength of a single fiber bundle is also examined. The experimental results reveal that the bulk density increased with the molding temperature up to 130°C and was saturated at a constant value above 130°C due to a decrease in the void content. This is because of the parenchyma cells of the fibers melt as the molding temperature rises. The tensile and bending strengths of the composite depend on the molding temperature. These strengths increased with the molding temperature up to 130°C as well as with the bulk density. This increase in the strengths was achieved by improving the adhesive property. However, the strengths of the composite decreased above 130°C due to the decomposition of the single fiber by heating. Thus, it was clarified that the optimum molding temperature was approximately 130°C. In addition, it was also clarified that the molding pressure has no effect on the bulk density, the tensile strength, and the bending strength of the pressed products.

抄録全体を表示

Joints must be the most common source of failure in any structures. Especially, aircraft structures are strongly demanded to reduce their weight keeping structural reliability in higher level. In recent years, as composite materials became applied more and more in aircraft structures, there exist many composite/metal mechanical joints. So, it is important to make clear the damage behavior of composite/metal mechanical joint. Authors proposed the method to monitor the mechanical behaviors using the fastener bolt embedded an optical fiber sensor, i. e. Smart bolt. In this paper, we try to apply this method to detect the early stage of bearing damage around fastener holes of composites. The results are summarized as follows; (1) we can detect the damage by the change of inclination in the relationship between load and axial strain measured by Smart bolt, and (2) it was shown that the early stage of damage of composites around the fastener hole can be detected by using Smart bolt

抄録全体を表示

Polymers have desirable mechanical properties and have been widely used as structural materials instead of metals under severe mechanical conditions. The molecular chain network model based on J₂-flow theory and Argon's hardening law cannot directly express a deformation-induced orientation of molecular chains, a propagation of high strain rate shear band and a nonlinear viscoelastic response before the initial yielding that is an inelastic behavior peculiar to polymer. In this paper, a new concept of “molecular chain slip system” is analogically proposed on the basis of crystal plasticity theory for metals. A molecular chain plasticity model that can reproduce the large deformation behaviors of glassy polymer mentioned above is developed by allowing an independent rotation of a slip system differently than the usual crystal plasticity framework. Moreover, the inelastic response law based on a probabilistic theory considering change of local free volume is adopted as a hardening law so as to express the nonlinear viscoelastic response.

抄録全体を表示

Polymers have desirable mechanical properties and have been widely used as structural materials instead of metals under severe mechanical conditions. In the previous paper, a new concept of “molecular chain slip system” is analogically proposed on the basis of crystal plasticity theory for metals. Moreover, an inelastic response law based on a probabilistic theory considering change of local free volume is adopted as a hardening law. However, the validity of this model is not numerically proved in detail. In this paper, we explain a method of large deformation analysis for glassy polymer using the present model. A finite element simulation is carried out for PMMA under plane strain tension. Macroscopic neck propagation with high strain rate shear band and directions of molecular chains in the oriented region are computationally visualized. It is indicated that independent rotation of slip systems can express an orientation hardening without constitutive equation of backstress. Furthermore, a nonlinear viscoelastic behavior that cannot be expressed by the conventional hardening law is accurately predicted

抄録全体を表示

Rotating bending tests and tension-compression fatigue tests on non-combustible magnesium alloy were carried out to investigate effect of mean stress on fatigue strength at N=10⁷. The ignition point of non-combustible magnesium alloys is about 300 K higher than that of normal magnesium alloys because of calcium addition. It was clarified as follows. (1) In the range of σ_m=0100MPa, fatigue strength at N=10⁷ of small hole specimens was about 30150% higher than that of small crack specimens. (2) In the range of σ_m>100MPa, fatigue strength at N=10⁷ of small hole specimens decreased because of static cracks initiating around small hole at the first loading. (3) In the range of σmax<σ_0.2, fatigue strength at N=10⁷ of smooth specimens was estimated using modified Goodman diagram.

抄録全体を表示

This paper describes the effect of anodic oxide film on fatigue behaviour of wrought magnesium alloys. Rotating bending fatigue tests have been performed using smooth specimens with anodic oxide films in laboratory air and demineralized water. Two different anodic oxide films, Mg-Hard and Mg-Light, were evaluated, in which both films had the same thickness of 30 μm, but the former had considerably higher hardness than the latter. In laboratory air, the fatigue strength of the anodized specimens with Mg-Hard was nearly the same as, or slightly higher than, that of the bare or untreated specimens, while the anodized specimens with Mg-Light exhibited higher fatigue strength than the bare specimens. In demineralized water, the fatigue strengths of both anodized specimens were the same as these of the bare specimens, indicating no improvement of corrosion fatigue strength by the anodic oxide films. This was because pores and crackings preexisted within the anodic oxide films acted as penetration path of the solution, thus similar corrosion fatigue process to the bare specimens took place underneath the anodic oxide films.

抄録全体を表示

Stress corrosion cracking (SCC) in structural metal materials occurs by initiation and coalescence of micro cracks, subcritical crack propagation and multiple large crack formation or final failure under the combination of materials, stress and corrosive environment. In this paper, a Monte Carlo simulation for the process of SCC has been proposed based on the stochastic properties of micro crack initiation and fracture mechanics concept for crack coalescence and propagation. The emphasis in the model is put on the influence of semi-elliptical surface cracks. Numerical simulations are carried out based on CBB (creviced bent beam) test results of a sensitized stainless steel SUS 304 and the influence of micro crack initiation rate and coalescence condition on the simulation results is discussed. The numerical examples indicate the applicability of the present model to a prediction of the SCC behavior in real structures.

抄録全体を表示

Tensile tests of notched thin film of pure titanium were carried out on the stage of a digital microscope. Tensile load was generated by the thermal expansion of a pair of polycarbonate loading plates by which the specimen was sandwiched. Since the thermal expansion coefficient of polycarbonate is much larger than that of pure titanium, the specimen was elongated with an increase in the temperature and successfully fractured at the end of the tensile test. The plastic deformation of the notched part of specimen was observed during the test and the stress and strain were evaluated. The obtained stress-strain curve situated between two curves by a commercial tensile testing machine at the room temperature and at 363 K, which approximately corresponds to the maximum temperature of the thermal stress-actuated tensile test. As the mechanism of the proposed tensile test is simple, it is expected to be applicable to much smaller specimens in the future.

抄録全体を表示

The in-plane static and impact compression phenomena of aluminum honeycombs were experimentally investigated. Particularly, the effect of strain rate on the deformation of honeycomb was studied. Also, by defining a “cell-scale strain” and a “macro-scale strain” in the present paper, the relationship between them in the deformation process of individual cells and that of the entire honeycomb was investigated. As a result, it was found that the strain rate affected the position of a localized condensation and the plastic collapse mode of cells and the cell-scale strain and macroscale strain showed different behaviors in the honeycombs. Moreover, the critical impact velocity for the transition of collapse modes was estimated.

抄録全体を表示

This paper describes the result of basic study for development of energy absorption structure with pressure bulkhead for railway vehicle made of aluminium alloy. Under U. K. standard, quasi-static compression test using full size specimen and finite element analysis was carried out. In the experiment, the structure was fully compressed up to collapse length of 445 mm and the absorbed energy 1.11 MJ. Maximum reaction force is almost less than 3000 kN with some spiked loads that exceeds 3000 kN. In the simulation, four nodes shell element was used for modelling and explicit finite element analysis method was employed. And the simulation results have good agreement with the experiment results in collapse length and load relationship. As a result, we have confirmed that the structure for the specimen can meet U.K. standard and our simulation method can predict collapse characteristics with practically high accuracy.

抄録全体を表示

In this work a new theory for estimating the maximum flaw-size distribution and the fracture strength distribution of a macroscopic ceramic body is presented, without using any fracture data except the fracture toughness. First, Gamma function was selected as the most suitable distribution function for flaw-size. The unknown parameters were estimated using the local flaw-size data obtained by Yao et al. ⁽⁵⁾ , who used a small thin ceramic specimen. The maximum flaw-size distribution function for a macroscopic ceramic body, which has an arbitrary volume, was derived based on the extreme statistics by taking the local flaw-size data as an initial distribution. Finally, the strength distribution function was derived using fracture mechanics. The validity of this theory was examined by comparing the Weibull parameters estimated from the theory with the experimental ones by Yao et al.

抄録全体を表示

Effects of ultrasonic peening on fatigue life of pad welded joint were analyzed by fatigue life analysis method by RPG load. It's noted that the ultrasonic peening is one of the most effective method for improving fatigue life of welded joint. Ultrasonic Impact Treatment, UIT, was adopted in this study as the ultrasonic peening method. A significant increase in fatigue life was observed on the pad welded joint with UIT treated weld toe. The improvement was estimated mainly due to compressive residual stress introducing, stress concentration reducing and grain refining in weld toe area. Estimated fatigue life by FLARP was consistent with experimental result.

抄録全体を表示

This paper describes the experimental results of the ultrasonic welding of glass and aluminum. Ultrasonic welding has made possible the welding of various glasses, such as Borosilicate glass and Soda-lime lass, to aluminum sheet at the room temperature, both quickly and easily when compared to other welding methods. For example, the ultrasonic welding of A1050H and Borosilicate glass can be accomplished under the conditions of amplitude of ultrasonic horn top 20μm, welding pressure 5 MPa, at a required duration of 0.4s. When cleaned with forced ultrasonic vibration, the contact surfaces need no further surface treatment. Moreover, the material can be processed easily, the operation produces little heat, and there is virtually no resultant weakness of the product.

抄録全体を表示