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Authors: K.S. Park, B.J. Kim, Young Hoon Moon
Abstract: In the tube hydroforming process, a tube is placed into the die cavity and the ends of the tube are sealed by fixing the axial cylinder piston into the ends. Then the tube is pressurized with a hydraulic fluid and simultaneously the axial cylinders move to feed the material into the expansion zone. In this study, the empirical and the quantitative relationship between process parameters and hydroformabillity are analyzed by fuzzy rules. Fuzzy expert system is an advanced expert system which uses fuzzy rule and approximate reasoning. Many process parameters are converted to the quantitative relationship by use of approximate reasoning of fuzzy expert system.
Authors: Yuan Song Zeng
Abstract: In this paper, the internal rolling process is presented to connect the titanium tubes to the tube fitting with the mechanical method. The material flow, the distribution of stress and strain and the connecting mechanics are analyzed by using the finite element method(FEM) for two kinds of the tube fitting structures, the triangle grooves and the rectangle grooves. Rolling experiments and tests for pressure durability, gas-sealing ability, surface finish and contact percent are also introduced. Results show that the tube joints with the triangle grooves has very excellent connecting strength, and the FE analysis agrees well with the experiments.
Authors: Shi Fang Xiao, Yu Hu Wang
Abstract: The uniaxial compressive mechanical properties of nanocrystalline Fe are simulated with a molecular dynamics technique and the analytical embedded-atom method. An asymmetrical mechanical phenomenon between tensile and compressive process is found, and the yield stress and flow stress in compression are higher than those in tension simulations. The compressive deformation process can be described as three characteristic regions: quasi-elastic deformation, plastic flowing deformation, and strain strengthening. During the plastic flowing deformation region, the material shows very good compressive ductibility. The plastic deformation is mainly dominated by the grain boundary atom slide.
Authors: Y.S. Choi, T.A. Parthasarathy, D.M. Dimiduk, M.D. Uchic
Abstract: The [001] tensile and compressive flow behavior of a single crystal superalloy CMSX-4 was simulated using a “unit-cell” mesh to represent the γ/γ′ microstructure. The simulation results showed a tension-compression (T-C) asymmetry, where the magnitude of the flow stress is larger in the elastic-plastic transition regime in tension, and is larger in compression in the plastic (flow softening) regime. The T-C flow behavior was related to the flow response of the γ-phase matrix under the geometric and kinematic constraint of the γ/γ′ unit cell.
Authors: M. Zhang, W.L. Zhang, M.Y. Gu
Abstract: To improve the transverse properties of fiber-reinforced metal matrix composites, a three-phase material model was proposed. In the model the reinforcing fibers are surrounded by a weak metal matrix, which in turn is encircled by another strong metal matrix. The weak matrix acts as a role to protect the fibers from damage and the strong matrix acts as a role to improve the transverse properties of the composite. Based on the material model, FEM model was established and parameter analysis was carried out to determine the influence of matrix strengths and fibers spatial distribution on the transverse mechanical behavior of the three-phase composite. It was found that the yield strength of the three-phase composite was mainly dictated by the matrix directly surrounding fibers and the effect from another matrix on the yield strength can be neglected. The three-phase composite has a higher transverse strength with hexagonal fiber arrangement than with regular square fiber arrangement.
Authors: Qi Jin Huang, Guo Quan Liu, Yong Li, Jin Ji Gao, Zheng Qiu Gu, Yu Zhen Ma, Hai Bin Xue
Abstract: Nucleus prosthesis replacement is considered as an ideal solution to low back pain. The purpose of this paper is to predict the suitable material properties and shape for the nucleus prosthesis of Chinese people based on biomechanical analysis using three-dimensional (3D) finite element (FE) method combined with experiments. The results suggest that a pillow-shaped nucleus prosthesis made of the polymer biomaterial with a Young’s modulus of 0.1-100 MPa is qualified to replace the degenerated nucleus. Then under the guidance of the FE predictions, a novel nucleus replacement material of polyvinyl alcohol hydrogel was prepared; the mechanical experiment shows that it has a compressive modulus of 1.0-6.8 MPa over a strain range of 10-60 %. The finite element predictions and experimental results have implications for the nucleus prosthesis designs.
Authors: B.J. Kim, S.M. Son, K.S. Park, Young Hoon Moon
Abstract: Modern automobiles are built with a steadily increasing variety of materials and semifinished products. The traditional composition of steel sheet and cast iron is being replaced with other materials such as aluminum and magnesium. But low formability of these materials has prevented the application of the automotive components. The formability can be enhanced by conducting the warm hydroforming using induction heating device which can raise the temperature of the specimen very quickly. The specimen applied to the test is AA6061 extruded tubes which belong to the age-hardenable aluminum alloys. But in the case of AA6061 age hardening occurs at room temperature or at elevated temperatures before and after the forming process. In this study the effects of the heating condition such as heating time, preset temperature, holding time during die closing and forming time on the hydroformability are analyzed to evaluate the phenomena such as dynamic strain hardening and ageing hardening at high temperatures after the hydroforming process.
Authors: Yue Jiang, Zhong Da Yin, Peng Chao Kang, Yong Liu
Authors: Jian Qin Mao, Hai Shan Ding, Hui Bin Xu, Cheng Bao Jiang, Hu Zhang
Abstract: A mechanical properties prediction model for cobalt-free maraging steel was built upon the experimental data by fuzzy identification method. A method of fuzzy identification based on fuzzy clustering and Kalman filtering is proposed. The results showed that good correlations between the predicted result and the experimental data. The technique proposed could be served as a reliable tool for cobalt-free maraging steel mechanical properties control and design.
Authors: Yang Shao, X. Zhang, Fu Ling Tang
Abstract: We successfully developed the potential parameters for simulation of MgB2. With these potential parameters, we calculate the lattice parameters and volume variations with pressure up to 240GPa. All these results agree well with experimental data under 40GPa and provide reasonable tendencies from 40GPa to 240GPa. By employing the McMillan expression, it is found that the lattice stiffening dominants the behavior of Tc under pressure in the scope of BCS theory. Using our calculated Grüneisen parameter G g , the simulated pressure effect on Tc accords well with experimental results. Our result shows that the Tc of MgB2 can be destroyed by high pressure.

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