The level-set method is becoming one of the most effective tools for predicting the shape and position of moving interfaces. However, this method has not yet been fully developed in the area of mechanics of materials, where interfaces, are generally treated as discrete entities. In this work, numerical simulations of an interface motion associated with a diffusion-driven phase transformation are performed using the level-set method. The constitutive relation of the mobile interface, linking its thermodynamical driving force with its velocity, is derived from the dissipation function. The governing partial differential equation for the coupled diffusion field-level-set function was motivated by the original work of Adalsteinsson and Sethian (2003), and is here developed further to enforce the requirement that Fick's second law be satisfied locally in a direction normal to the interface. The coupled diffusion-level-set model is implemented into the finite element method and is then used to solve a phase transformation problem in a Ni-base superalloy.

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In this paper, we describe the structure analysis by the finite element method of the gas-inflatable membrane structure with initial shape before pressure loading, on the assumption of the structure analysis of the gas-inflatable membrane reflector. The initial shape is assumed to be a paraboloid of revolution or similar shape. In the finite element formulation, to consider the influence of the initial shape, the strain based on the extensional strain is introduced. The experiment is also conducted to compare with the numerical calculation result. The agreement of the experiment result and the numerical result shows that our finite element formulation is appropriate.

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Copper electroplating is widely used for fabrications of Large-Scale Integration (LSI) besides other methods such as sputtering because of its excellent via/trench filling ability, good adhesion and lower process temperature and low cost. In the electroplating process, real-time estimating a growth rate of electroplating is essential. It is possible to estimate the growth rate of electroplating from the current density on the LSI wafer surface because the rate is mainly proportional to the current density. In this paper, a new monitoring method to estimate the LSI plating current density distribution from electric potentials in the plating bath is developed. The proposed method measures electric potentials at several points in the bath using capillaries, and estimates the current density on the LSI wafer surface by applying an inverse analysis method. In the inverse analysis, an observation equation is modeled by considering that the electric potentials in the bath obey the Laplace equation, which is solved by Bayesian estimation. In order to demonstrate the effectiveness of the proposed method, numerical simulations which involve measurement errors are performed for a sample polarization curve of Cu in CuSO₄. The results show that this method could be applied to practical problems. In addition, using a priori information for the possible shape of the polarization curve, the estimate accuracy of the proposed method is shown to be improved.

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A reamer bolt is widely used when clamping a joint subjected to large shear forces. It has been postulated in some conventional joint design procedure that the applied shear force is transmitted only through the normal force exerted on the cylindrical body of reamer bolt. However, it is also supported, to some extent, by the friction force on contact surfaces involved. Accordingly, in order to establish a design procedure that takes account of the joint safety and efficiency, it is primarily important to evaluate the ratios of the shear forces supported by the reamer surface and the friction force. They are quantitatively evaluated by defining shear force transfer ratio (SFTR). It is predicted that SFTR is largely affected by the fit and the surface condition of the interface between reamer bolt and bolt hole. In this study, the amounts of SFTR are evaluated using three-dimensional FEM as contact problems. Numerical results show that SFTR by the friction force is significant, which implies that the conventional design procedure for bolted joints tightened by reamer bolts needs to be modified. The validity of the numerical analysis proposed here is demonstrated by experimentation, in which measured are the bending stresses in reamer bolts under shear loads. It was found that the numerical results favorably agreed with the experimental ones.

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The finite element models of the Bernoulli-Euler beam theory and Timoshenko beam theory are now standard. The Timoshenko beam theory allow for the effect of transverse shear deformation which has been neglected in the Bernoulli-Euler beam theory. The first author developed a beam element based on a displacement formulation of Timoshenko beam theory. The objective of this paper is to present a formulation for beam element based on the new beam theory proposed by Endo and Kimura. In this theory, the transverse displacement w is taken as a sum of two partial displacements, one part, w_b, due to bending, and the second, w_s, due shear displacement. The efficacy of the present beam element is demonstrated through the numerical example of static flexure.

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Micromechanical analysis of a composite material containing many ellipsoidal reinforcements is performed by using the equivalent inclusion method combined with the Mori-Tanaka theorem. Eshelby tensor for the reinforcement is rearranged as a function of Poisson's ratio of the matrix multiplied by the geometrical factor and is used in the analysis. The geometrical factor is only a function of the aspect ratios of reinforcement and is named by the authors. Since all reinforcements are assumed to align along the same direction in the modeling, the composite material has three perpendicular two-fold rotational symmetries. Therefore, nine components of the macroscopic elastic constant of the composite are derived as a function of the geometrical factor of reinforcement. Moreover, macroscopic coefficients of thermal expansion for the composite are also expressed successfully.

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Three point bend specimen is used for ductile fracture tests with different mixed mode ratio, K_II/K_I. The crack growth direction in mid-plane of the specimen changes largely with the change of K_II/K_I value. Detailed observation of fracture surface is conducted, and it is shown that the average void diameter becomes smaller as K_II/K_I becomes lager. Numerical simulation is also carried out using Gurson's yield function. By introducing stress-controlled void nucleation model, as well as plastic-strain-controlled nucleation model, it is shown that crack growth directions at mid-plane and tree surface are estimated well and results agree with experimental observations qualitatively. Distributions of stress triaxiality and plastic strain are also evaluated and their effects on dimple fracture process are discussed.

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Fatigue crack growth under mixed mode loading conditions is simulated using S-FEM. By using S-FEM technique, only local mesh should be re-meshed and it becomes easy to simulate crack growth. By combining with re-meshing technique, local mesh is re-meshed automatically, and curved crack path is modeled easily. In the previous paper, basic problems were solved, and availability of this method was verified. In this paper, interaction of two parallel cracks with different level is studied. By changing relative locations of two cracks, totally 161 cases are solved, and results are summarized by normalized form. It is shown that there is a clear area in which interaction between two cracks is not neglected. A new criterion to evaluate interaction effect between two parallel cracks is proposed.

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The crack path of 12Cr martensitic stainless steel tempered at low temperature is intergranular in the case of delayed failure and transgranular in the case of corrosion fatigue. The effect of varying load on the transition of crack path in delayed failure was examined. Delayed failure test was done in pure water under triangularly varying load. The crack path was dependent on load frequency. Higher frequency resulted in transgranular crack and lower frequency resulted in intergranular crack. There was a threshold frequency below which intergranular crack could appear. An insertion of a few cycles of rapid loading into the low frequency loading which usually resulted in intergranular crack caused the transition into a transgranular crack.

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In the failure analysis of fatigue fracture, the estimation of applied stress by examining the fatigue fracture surface is important in order to investigate the cause of failure. A fractographic method using striations has been established. Striations, however, can be observed only when a crack propagated at relatively high rate. In the case of failure after a long period of operation under low stress condition, striations are rarely observed. The estimation of applied stress is almost impossible in such a case. Therefore, an estimation method which can be applied in the low stress intensity region where striations are not observed is desirable. In this study, the applicability of micro hardness measured directly on the fatigue fracture surface as a parameter for the stress estimation was examined. The hardness of fatigue fracture surface was correlated with the stress intensity factor range. In addition, as an approach to service load, the relationship between the hardness of fatigue fracture surface and K value was investigated using repeated two-step stress.

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In this study, evaluation method for fatigue crack growth rate under large scale yielding condition was investigated based on J integral range, ΔJ, Low cycle fatigue crack growth tests were conducted using compact tension (CT) specimens of SM 400B steel with some sizes of plate thickness. As the results, thickness effect appears in the relationships between fatigue crack growth rate and ΔJ calculated by Merkle and Corten's conventional equation. Moreover, ΔJ and P-V (load versus load line displacement) curves were analytically calculated using cyclic stress-strain curves based on 2σ_y concept as the FEM constitutive equation. 2σ_y concept is that yield stress is approximately set to about double magnitude of yield stress obtained from tensile test. It was found that P-V curves using in calculating ΔJ were approximately coincident by taking account of stress triaxiality factor at the crack tip obtained from above FEM analysis in addition to thickness. Therefore, conventional equation of ΔJ was modified by the stress triaxiality factor. Fatigue crack growth rates could be predicted by the modified ΔJ without depending on the size of thickness.

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Based on a two dimensional physical model of a mode I crack with a slip band, the analysis of mechanical interaction between hydrogen and dynamic dislocations with non-steady emission from a stressed source around a crack tip was conducted. To analyze the mechanical interaction between a crack and dynamic dislocations on a neighboring slip band, a crack is replaced by static discrete dislocations mechanically equivalent with the crack and a physical model of analyzing the mechanical interaction between static, dynamic dislocations and hydrogen was constructed. The occurrence conditions of the mechanisms of corrosive anodic chemical reaction, inter-granular cracking due to hydrogen concentration and facet like fracture due to the interaction between hydrogen and dynamic dislocations were clarified. These results were found to be in good agreement with previous results based on a convenient one dimensional model. Furthermore, the competitive interaction between hydrogen and dynamic dislocations which causes the facet like fracture was found to occur under the limited velocity range of hydrogen and dynamic dislocations which is closely related to the corresponding range of yield stress.

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Strain distribution in deformed polycrystalline iron plates was investigated using digital image correlation analysis of scanning electron microscope (SEM) images observed before and after tensile tests. Orientation of grains was determined by electron backscattering diagrams (EBSD). Magnitude of strain below 1% could be detected with spatial resolution of 8×8μm² by the digital image correlation analysis. Inhomogeneous strain distribution was observed in and among grains. It was pointed out that the information of activated slip systems could be obtained by the ratio of strain along the three directions. It was found that the deformation was not always caused by the activation of the slip system of the largest Schmid factor.

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The simple overstress model is first shown, which is extended so as to describe the smooth elastoplastic transition by formulating the viscoplastic strain rate induced by the scalar-valued overstress describing the expansion from the subloading surface to the dynamic-loading surface. Then, the tangential viscoplastic strain rate is described by introducing the overstress tensor denoting the difference of the current stress tensor on the dynamic loading surface from the elastoplastic stress tensor on the subloading surface. Here, the elastoplastic stress is formulated by substituting the viscoplastic strain rate in stead of the plastic strain rate into the evolution rules of not only internal variables but also subloading ratio, i.e. the ratio of the size of the subloading surface to that of the normal-yield surface in the elastoplastic constitutive equation. Further, the generalized overstress model is formulated in which the existence of purely elastic domain observed in metals is assumed and the existence of the limit in the expansion of the dynamic-loading surface is introduced so that it is capable of describing the deformation at general rate from the quasi-static deformation to the impact load.

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The ultrasonic welding technique can be carried out in many different ways, such as in direct welding metals both quickly and easily when compared to other welding methods. This paper gives a description of an experimental study of the ultrasonic welding of aluminum and cupper under water bath. For example, the ultrasonic welding of Al (t : 0.2) /Cu (0.2) can be accomplished when the conditions of welding pressure : 20MPa, at a required duration of 1.0s under water welding. Moreover, the material can be processed easily, and it gives out little heat, and hardly gets weakness.

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