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Nonlinear Finite Element Analysis of Composite Shell Under Impact
Cho, Chong-Du,Zhao, Gui-Ping,Kim, Chang-Boo The Korean Society of Mechanical Engineers 2000 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.14 No.6
Large deflection dynamic responses of laminated composite cylindrical shells under impact are analyzed by the geometrically nonlinear finite element method based on a generalized Sander's shell theory with the first order transverse shear deformation and the von-Karman large deflection assumption. A modified indentation law with inelastic indentation is employed for the contact force. The nonlinear finite element equations of motion of shell and an impactor along with the contact laws are solved numerically using Newmark's time marching integration scheme in conjunction with Akay type successive iteration in each step. The ply failure region of the laminated shell is estimated using the Tsai- Wu quadratic interaction criteria. Numerical results, including the contact force histories, deflections and strains are presented and compared with the ones by linear analysis. The effect of the radius of curvature on the composite shell behaviors is investigated and discussed.
Cho, Chong Du,Lee, Heung Shik,Kim, Chang Boo,Beom, Hyeon Gyu Trans Tech Publications, Ltd. 2006 Key Engineering Materials Vol.306 No.-
<P>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.</P>
Analysis of Electro-Statically Driven Micro-Electro-Mechanical Systems
Cho, Chong Du,Lee, Byung Ha Trans Tech Publications, Ltd. 2006 Key Engineering Materials Vol.306 No.-
<P>In this paper, a methodology of modeling and simulating the electro-statically driven micro-electromechanical systems (MEMS) is presented, utilizing topography data with an arbitrary structure. In the methodology, the mask layout and process recipe of a device are first generated and the model then discretized by an auto-mesh generation for the finite element analysis. Finally the analysis is performed to solve the Laplace and the dynamic equation at a time. The methodology is applied to an electro-statically driven comb-drive as a test vehicle for verification.</P>
디스코 브레이크에서 열섬 현상이 발생되는 원인과 저더진동에 미치는 영향
조종두(Cho, Chong-Du),김명구(Kim, Myoung-Gu),조호준(Cho, Ho-Joon) 한국소음진동공학회 2006 한국소음진동공학회 논문집 Vol.16 No.8
Hot spot phenomenon is caused by non-uniform contact area between brake pad and disk frequent braking. Brake disk deformed by locally concentrated heat increases magnitude of frictional vibration. And this deformation can highly influence the judder vibration. In this experimental study, vibration and hot spot was measured in accordance with rotation of disk and pressure of master cylinder for finding the factors that causes hot spot phenomena. For comparing hot spot aspects with mode shapes of disk, mode shapes were measured by conducting modal test, and analyzed by using finite element analysis. Relation between hot spot phenomenon, and mode shape, pressure of master cylinder and rotation speed of disk respectively, was achieved by hot spot measurement and frequency analysis.