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Application of Computational Welding Mechanics and Inherent Strain |
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Computational welding mechanics is a vital tool to understand the complex transient phenomena in welding. On the other hand, the welding residual stress and the distortion are produced by inherent strain or inelastic permanent strain. Once the relation between the welding parameters and the inherent strain distribution is established, the residual stress and the deformation can be predicted by elastic analysis using inherent strain as initial strain. |
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Optimization and Control of Spot Welding Process |
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One of the promising fields for the application of computational welding mechanics is the optimization and control of the welding process. The resistance spot welding is the ideal process to apply the computational mechanics because the fluid flow in the nugget can be neglected. The authors developed a FEM code to solve the electric, the thermal and the mechanical fields sequentially with small time step. Using this method, the welding process of the joint with initial gap is closely studied and the possibility of process control based on the electrode displacement is demonstrated. |
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Simple model for Crack Propagation Problems |
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Crack propagation can be considered to be a process to create new surface. Therefore, computational models for crack propagation must include not only the mechanism of deformation but also that of surface formation. The authors developed a simple surface formation model using the interface element. The interface elements are applied to static and dynamic crack propagation problems in elastic, elasto-plastic and composite materials. |
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Mechanical Study of Hot-Cracking in Welding |
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Though numerous numbers of reports are published on hot cracking in welding, most of them are research works from metallurgical aspects. The number of papers reporting the mechanical aspect of the phenomena is quite few. The authors developed a temperature dependent interface element and apply it to simulate the Houldcroft test using fishbone type specimen. |
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High-Temperature Properties of Newly Developed SiC Fibers |
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To estimate the suitability of newly developed SiC fiber (Hi-Nicalon type S) for reinforcement of ceramic matrix composites, fiber tensile tests at high temperature, fiber oxidation tests and fiber bend stress relaxation tests were carried out. The results of tensile tests at high temperature indicated that the strength of Hi-Nicalon type S did not decrease with increasing test temperature. The oxidation behavior of Hi-Nicalon type S was found to fit the Deal/Grove linear-parabolic model. Finally, Hi-Nicalon type S fibers were more resistant to bend stress relaxation than Hi-Nicalon fibers. |
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Development of A Simple Model for Creep Analysis of Thick Welded Joint |
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A simple model was developed for creep theoretical analysis of thick welded joint. The model is easy to treat, and needs only a little labor and computation time to predict the creep behaviors of the thick welded joints. It was verified by comparing the estimated results with experimental ones that the model can accurately simulate the creep behaviors of the thick welded joints (the creep curve of the joint, the local strains of the weld metals and base metal, and the creep life of the joint). |
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Thermal Stress Analysis of Brake Disk of Super Express Train |
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Thermal stress produced in a brake disk when a super express train is braked rapidly is being analyzed. In the case the material of the brake disk is a new composite one, cracking may occur due to the large thermal stress. The material properties are being investigated, and the thermal stress is being calculated by the finite element method. |
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Development of Dynamic Model of Tubular Idealized Structural Unit for Nonlinear Analysis of Offshore Tubular Frames |
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The idealized structural unit method is a kind of very efficient finite element method. First, the tubular unit was developed for static analysis. The unit is being expanded for dynamic analysis, the dynamic influential factors (inertial force, dependency of material property on strain rate, dynamic buckling, etc) being considered. |
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Effectiveness of Various Stiffeners on Stiffness and Strength of Joint of Offshore Tubular Frame |
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The strength of the joint is very important to ensure the strength of the whole structure. The reinforcement method of the joint is important, too. In this study, efficient type, shape and size of stiffener and its optimum position are being investigated. |
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