Progresses in Fracture and Strength of Materials and Structures

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Authors: Seok Young Han, M.S. Kim, S.H. Choi, J.Y. Park, Byung Ju Yi
Abstract: A material mixing method to obtain an optimal topology for a structure in a thermal environment was suggested. This method is based on Evolutionary Structural Optimization (ESO). The proposed material mixing method extends the ESO method to a mixing several materials for a structure in the multicriteria optimization of thermal flux and thermal stress. To do this, the multiobjective optimization technique was implemented. The overall efficiency of material usage was measured in terms of the combination of thermal stress levels and heat flux densities by using a combination strategy with weighting factors. Optimal topologies having multiple thermal criteria for a printed circuit board (PCB) substrate were presented to illustrate validity of the suggested material mixing method. It was found that the suggested method works very well for the multicriteria topology optimization.
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Authors: Seok Young Han, J.Y. Park, Y.D. Kim, S.J. An, J.S. Maeng
Abstract: An active micro-mixer equipped with an oscillating stirrer is considered by analyzing the mixing behaviors, i.e. the effect of the Karman vortex, the flow structure after the stirrer, etc. The mixing was calculated by the D2Q9 model of Lattice Boltzmann methods. In this study, the time– averaged mixing index formula, I D , is newly proposed for time dependent flow. Three models are tested and the mixing indices are compared. From the results, it was found that the mixing of Model III is enhanced and stabilized much more than the other models. Therefore, an optimum design for a dynamic micro-mixer with an oscillating stirrer was performed. The design variables were established as the length, the angle and frequency of the stirrer. It is found that the optimal design variables are determined by 0.66, 107.9 o and 0.49 Hz.
2836
Authors: Seok Young Han, S.J. Yoon, S.R. Kim, J.Y. Park, Byung Ju Yi, S.J. Kim
Abstract: Sufficient workspace and high natural frequency of a micromanipulator are the fundamental requirements in its design. In this study, a previous design was analyzed from the viewpoint of the axiomatic design. Then, a new design parameter as displacement amplifier which transforms a coupled design into a decoupled design, was suggested. And a design procedure based on axiomatic design was developed. A planar 3-DOF parallel-type micromanipulator was chosen as an exemplary device. According to the suggested design procedure, the micromanipulator having the required natural frequency was designed in the first step, and then the displacement amplifier satisfying the required work space was designed sequentially. To check the effectiveness of the manipulator and displacement amplifier, simulations and experiments were performed. Those are verified that the displacement amplifiers implemened work very well for satisfying the required task workspace.
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Authors: Seok Young Han, S.J. Yoon, S.R. Kim, J.Y. Park, Byung Ju Yi, S.J. Kim
Abstract: The micromanipulator is basically required sufficient workspace and high natural frequency. However, previous designs are hard to satisfy the required workspace and natural frequency simultaneously. In this study, a previous design was analyzed from the viewpoint of the axiomatic design. Then, a new design parameter as displacement amplifier which transforms a coupled design into a decoupled design, was suggested. And a design procedure based on axiomatic design was developed. A spatial 3-DOF parallel-type micromanipulator was chosen as an exemplary device. According to the suggested design procedure, the micromanipulator having the required natural frequency was designed in the first step, and then the displacement amplifier satisfying the required work space was designed sequentially. To check the effectiveness of the manipulator and displacement amplifier, simulations and experiments were performed. Those are verified that the displacement amplifiers implemened work very well for satisfying the required task workspace.
2843
Authors: S.H. Choi, M.S. Kim, J.S. Hwang, J.Y. Park, Seok Young Han
Abstract: Topology optimization of the inner reinforcement for a vehicle’s hood has been performed by evolutionary structural optimization (ESO) using a smoothing scheme. The purpose of this study is to obtain optimal topology of the inner reinforcement for a vehicle’s hood considering the static stiffness of bending and torsion, and natural frequency simultaneously. To do this, the multiobjective optimization technique was implemented. Optimal topologies were obtained by the ESO method. From several combinations of weighting factors, a Pareto-optimal solution was obtained. Also, a smoothing scheme was implemented to suppress the checkerboard pattern in the procedure of topology optimization. As the weighting factor of the elastic strain efficiency goes from 1 to zero, it is found that the optimal topologies transmits from the optimal topology of static stiffness problem to that of natural frequency problem. Therefore, it is concluded that ESO method with a smoothing scheme is effectively applied to topology optimization of the inner reinforcement of a vehicle’s hood considering the static stiffness and natural frequency.
2847
Authors: Ming Tu Ma, Xiao Feng Xiang, Zhi Gang Li, Hong Liang Yi, Hong Wu Bai, Hao Zhang
Abstract: The FEM was used to analyze the stress distribution of a motorcycle frame on the condition of normal running, starting up, turning and braking, respectively. Having been carrying on the 2000km of running test, the initial design motorcycle frame was found several cracks or fractures in the bending points of the square tube and in the welding seam, whose reasons were analyzed then. The metallographical structures of materials and crack parts of the frame were observed and analyzed and Q235. Based on the results mentioned above, the Q345 steel(Chinese steel mark) was used to replace the Q195 steel in the bending square tube and the prop of the steering column. And the welding and manufacture processes were optimized and improved. Finally, the motorcycle frame whose materials had been optimized could keep running in good condition and satisfy the demands after 16000km of running test.
2851
Authors: W.C. Lee, Chae Sil Kim, J.B. Na, D.H. Lee, S.Y. Cho, H.O. Choi, Jung I. Song
Abstract: Since most marine engines are generally very huge and heavy, it is required to keep safety from accidents in dealing them. Several types of lifting lugs have been used to assemble hundred ton–large steel structures and carry the assembled engines. Recently a few crashes have been occurred in carrying engines due to breaking down the lugs. Although the stability evaluation of the lifting lug has therefore been very important for safety, systematic design procedure of the lugs, which includes the structural analysis considering stability, has few reported. This paper describes the three dimensional finite element structural modeling for a lifting lug, the studies for determining the reasonable loading and boundary conditions, and the stability evaluation with the results of structural analyses. It should be very helpful for designing the other types of lifting lugs with safety.
2855
Authors: Dal Woo Jung, Nak Sam Choi
Abstract: Fatigue fracture behavior of a hybrid joint part for the tilting car body was evaluated in comparison to the case of static fracture. The specimens of hybrid joint part applied in the real tilting car body were fabricated for the bending test. Characteristic fracture behaviors of hybrid joint part specimens under cyclic loads were obviously different from the case under static loads. Static bending load caused the shear deformation and fracture in the honeycomb core region, while cyclic bending load did the delamination along the interface between composite skin and honeycomb core layers as well as the fracture of welded joint part. Experimental results obtained by static and fatigue tests were reflected in modifications of design parameters of the hybrid joint structure in the real tilting car body.
2860
Authors: Seung Bum Kwak, Nak Sam Choi
Abstract: Coolant rubber hoses for automobile radiators under thermal and mechanical loadings can be degraded and thus failed due to the influences of contacting stresses of air, coolant liquid and to the locally formed electricity. In this study, degradation behavior of the radiator hose made of EPDM rubber was evaluated. The thermo-oxidative aging test showed that the surface hardness IRHD of the rubber increased together with a reduction of failure strain. By the electro-chemical test it was shown that the penetration of coolant liquid into the skin of the rubber hose arose inducing an increase in weight of specimens as well as a decrease in failure strain and IRHD hardness. The penetration of coolant liquid altered considerably the micro-structure and the micro-hardness distribution along the depth in the rubber hose. On the basis of the above results failure mechanisms of degraded EPDM rubbers were suggested according to the kinds of contacting stresses.
2864
Authors: Zhao Zhang, Xi De Li, Wen Shen
Abstract: In this paper, a speckle microinterferometric system was employed to study the thermal deformation of the Cu microbridges with different dimensions. The deflections of the microbridges caused by the thermal loading were measured with real-time by the speckle microinterferometric system and the surface temperatures of the bridges were recorded using a digital thermometer. The deformation evaluation after microbridges buckling was also recorded with our testing system. Then, the experimental results were compared with the finite element analysis (FEA).
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