Papers by Author: Chang Boo Kim

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Authors: Chong Du Cho, Heung Shik Lee, Chang Boo Kim, Hyeon Gyu Beom
Abstract: In this paper, a finite element code especially for micro-magnetostrictive actuators was developed. Two significant characteristics of the presented finite element code are: (1) the magnetostrictive hysteresis phenomenon is effectively taken into account; (2) intrinsic geometric feature of typical thin film structures of large length to thickness ratio, which makes it very difficult to construct finite element mesh in the region of the thin film, is considered reasonably in modeling micro-magneostrictive actuators. For verification purpose, magnetostrictive thin films were fabricated and tested in the form of a cantilevered actuator. The Tb-Fe film and Sm-Fe film are sputtered on the Si and Polyimide substrates individually. The magnetic and magnetostrictive properties of the sputtered magnetostrictive films are measured. The measured magnetostrictive coefficients are compared with the numerically calculated ones.
Authors: Hyeon Gyu Beom, Y.H. Kim, C. Cho, Chang Boo Kim
Abstract: A thin electrode layer at the interface between two dissimilar linear piezoelectric materials under electromechanical loading is investigated. The complex function theory is employed to obtain the exact solution to a finite thin conductive layer. Special consideration is devoted to the structure of singular stress and electric fields near the tip of the thin electrode between two dissimilar piezoelectric materials. The stress and electric field are found to have an inverse square root singularity. The electric field intensity factor characterizes uniquely the singular fields close to the edge of the conductive line sheet.
Authors: Zheng Yang, Hyeon Gyu Beom, Chang Boo Kim, Chong Du Cho
Abstract: Single or multiple of delaminations have been found frequently on the fracture surface of X70 pipeline steel. In this study, the delamination cracks and their influence on the fracture of pipeline are investigated by both experiment and three-dimensional fracture analyses. It is shown that the three-dimensional stress state is prerequisite for delamination crack and the strength distribution of material influences the form and direction of delamination crack. The delamination cracks are produced on the weak interfaces among the material by the tensile stress perpendicular to them before the fracture passes. The direction of delamination crack depends on the three-dimensional stress fields and strength distribution of material near the crack tip or notch root. The delamination cracks of the fracture through thickness of pipe wall make the effective thickness decrease and the delamination cracks of surface crack are perpendicular to the direction of fracture propagation direction. The delamination cracks reduce the stress triaxiality near crack tip and in turn, improve the fracture toughness of X70 pipeline steel.
Authors: Chang Boo Kim, Chong Du Cho, Hyeon Gyu Beom
Abstract: This paper presents electro-mechanical characteristics of a micro-machined vibrating silicon ring gyroscope which can measure angular velocity components about three orthogonal axes. The ring gyroscope has a ring connected to the gyroscope main body by support ligaments that are arranged with cyclic symmetry. The natural modes of its vibration can be distinguished into the in-plane motion and the out-of-motion that are coupled by the gyro-effect due to the rotation of the gyroscope main body. The motions of the ring are electro-statically driven, sensed and balanced by electrodes. The equations of motion are formulated with considering the electrostatic effects of electrodes. The measuring method of angular velocities of the gyroscope main body by force-torebalance is proposed. The dynamic characteristics of the ring gyroscope are discussed.
Authors: Hong Wei Ma, Chong Du Cho, Chang Boo Kim, Hyeon Gyu Beom
Abstract: The bolted end-plate composite beam-CCSHRC column connection was validated to be ductile and offered an alternative to pre-Northridge connection. This study aims at the beam lower flange fracture in the connection test, and applies the J-integral criteria to examine the connection’s nonlinear fracture behavior. Advanced 3-D connection models containing initial crack in the high stress zone at lower flange are created, and the J values at the crack tip are calculated with considering the influences of certain parameters. The results demonstrate that the J values are strongly affected by the initial crack length and interstory drift. For 0.94, 1.35, 1.86 and 2.50 mm long crack, the J values sharply increase during loading history. The crack with a length of 2.50 mm propagates at a 66 mm drift, while the 1.35 mm long crack grows at a 120 mm drift. For 0.94 or 0.61 mm long crack, it keeps stable without growing upon loading. Besides, the J values exhibit a weak sensitivity to the beam concrete strength and tensile reinforcement ratio for beam. Under the same drift, the J-integral increases by about 3.5% when concrete strength changes from 15 to 24 MPa, and the J values at 0.6% tensile reinforcement ratio for beam are 1.5% larger than those at 0.3% or 1% reinforcement ratio.
Authors: Chang Hao Piao, Chong Du Cho, Chang Boo Kim, Qiang Pang
Abstract: This study tries to obtain the spring constant of welded metal bellows through experimental and numerical method respectively. The prediction of spring constant plays a great role in the design and application of the welded metal bellows. To derive the spring constant of the bellows, we employ commercial package to build up 2 axi-symmetric FEM models by using plane 42 and shell 51 elements. In the experiment, we use UTM to measure the spring constant of the bellows. And, the predicted spring constant resulting from the analysis is compared with the experimental one to discuss the rationality of spring constant analysis. The analytical results correspond well with experimental data and hence explaining the validity of FEM model.
Authors: Chang Boo Kim, Young Chul Ahn, Bo Yeon Kim, Chong Du Cho, Hyeon Gyu Beom
Abstract: In this paper, we present an efficient method for conducting a finite element analysis of a structure with cyclic symmetry and apply the method to analyze the natural vibration and linear and non-linear static characteristics of a blower impeller. A blower impeller is composed of circumferentially repeated substructures. The whole structure is partitioned into substructures, and the finite element analysis can thus be performed with one representative substructure by using the transformed equations for each number of nodal diameters, which are derived from a discrete Fourier transform. We calculated the natural vibration and linear and non-linear static characteristics of a blower impeller without a stiffening ring, and with small as well as large stiffening rings, respectively. The accuracy and efficiency of the presented method are verified by comparison of the results obtained from the analysis using a substructure to those obtained using the whole structure.
Authors: Myoung Gu Kim, Chong Du Cho, Chang Boo Kim, Ho Joon Cho
Abstract: Experimental and theoretical study of the non-planar response motions of a circular cantilever beam subject to base harmonic excitation has been presented in this paper work. Theoretical research is conducted using two non-linear coupled integral-differential equations of motion. These equations contain cubic linearities due do curvature term and inertial term. A combination of the Galerkin procedure and the method of multiple scales are used to construct a first-order uniform expansion for the case of one-to-one resonance. The results show that the nonlinear geometric terms are very important for the low-frequency modes of the first and second mode. The non-linear inertia terms are also important for the high-frequency modes. We present the quantitative and qualitative results for non-planar motions of the dynamic behavior.
Authors: Usik Lee, Jae Sang Lee, Chang Boo Kim
Authors: Chang Hao Park, Chong Du Cho, Chang Boo Kim, Hyeon Gyu Beom
Abstract: This study tries to analyze the torque generated in a micro-electromagnetic clutch by using FEM. For the purpose of design change and optimization of the micro-electromagnetic clutch, the torque prediction is very important. We employ a mathematical approach of the process based on electromagnetic principle. Then real material properties are substituted in the FEM model to obtain the analytical torque. For a test, the predicted torque is compared with the experimental one to discuss the rationality of torque analysis process. The analytical result agrees well with experimental data and hence explaining the validity of the mathematical process and the FEM model.
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