• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.3
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• pp.37-44
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• 2004

This paper deals with the performance analysis of LIPCA(Light-weight Piezo-Composite actuator) including the material nun-linearity of the embedded 3203HD PZT wafer. For this analysis, we used a piezo-shell element code based on a nine-node assumed strain shell element formulation. The material non-linearity was implemented in the formulation due to a large observed discrepancy between the measured displacement and the computed actuation displacement based on the linear analysis. An experimentally extracted piezo-strain function of the PZT wafer and incremental formulation were incorporated into the linear finite element code to improve the accuracy of the estimated actuation displacement of the LIPCA. The non-linear piezo-shell program was used to predict the non-linear performance of the LIPCA. The simulated actuation displacement from the non-linear code showed much better agreement with the measured data.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1993.10a
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• pp.212-217
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• 1993

A 2-dimensional FEM/GEM program was developed for analyzing forming processes of an arbitrarily shaped draw-die, in which plane strain condition is assumed and linear line elements are employed. FEM formulation adopted a new algorithm for solving force equilibrium as well as non-penetration condition simultaneously. For the case of numerical divergence at nearly final forming stages and the initial guess in Newton-Raphson iterations, geometric force equilibrium method(GEM) is also introduced. The developed program was tested with the simulation of stamping processes of automotive bonnet inner pannel in order to verify the usefulness and validity of FEM/GEM formulation.

• Journal of the Earthquake Engineering Society of Korea
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• v.5 no.3
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• pp.57-64
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• 2001

For the dynamic nonlinear analysis of stiffened plate and shell structures, total Lagrangian formulation is presented based upon the degenerated shell element considering finite rotation effects. Assumed strain concept is adopted in order to overcome shear locking phenomena and to eliminate spurious zero energy mode. In the elasto-plastic analysis, the return mapping algorithm based on the consistent elasto-plastic tangent modulus is applied to collapse analysis of shell structures. Newmark integration method is used for dynamic nonlinear analysis of shell structures under dynamic forces.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.3
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• pp.80-93
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• 1996

A 2-dimensional FEM/GEM program was developed under the plane strain assumption using linear line elements for analyzing stretch/draw forming operations of an arbitrarily shaped draw-die. FEM formulation adopted a new algorithm for solving force equilibrium as well as non-penetration condition simultaneously. Also, a rigid-viscoplastic material model with Hill's normal anisotropic yield condition and rate-sensitive hardening law is assumed, along with the Coulomb friction law in the contact regions. For the case of numerical divergence at nearly final forming stages, geometric force equilibrium method(GEM) is also introduced. The developed program was tested by simulating the forming processes of cylindrical punch/open die, and the drawing processes of automotive oilpan and hood inner panel in order to verify the usefulness and validity of FEM/GEM formulation. The numerical simulation verified the validity and robustness of developed program.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.3
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• pp.108-117
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• 2010

The frame element is commonly used for construction stage analysis PSC bridges. However, the frame element does not show sufficient information in the curved PSC box bridges. For the case of curved PSC bridges, the deformations in the inner and outer web are different. In this case, the different jacking forces are required in the inner and outer webs. And it is impossible to calculate different jacking forces in the inner and outer webs if we use the frame element for construction stage analysis. In order to overcome this problem, the use of shell element is essential for a three-dimensional construction stage analysis of PSC bridges. In the following, the formulation of an assumed strain shell element and its application of PSC box girder bridge analysis are presented.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.17 no.3
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• pp.279-293
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• 2004

The analysis of linear static and free vibration problems of isotropic and laminated composite plates and shells is performed by the improved 9-node shell element with the new strain displacement relationship. In that relationship, the effect of new additional terms between the bending strain and displacement has been investigated in the warping problem. Natural co ordinate based strains, stresses and constitutive equations are used. The assumed natural strain method is used to alleviate both membrane and shear locking behavior from the element. The Lanczos method is employed in the calculation of the eigenvalues of laminated composite structures and the Gauss integration rule is adopted to evaluate the mass matrix. The numerical examples are compared with the analytical solutions to validate the current formulation and the results presented could be useful for the understanding of the behaviour of laminates under free vibration conditions.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.1
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• pp.169-178
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• 1991

A plane-strain finite element analysis of sheet metal forming is carried out by using the rigid-plastic FEM based on the membrane theory. The sheet material is assumed to possess normal anisotropy and to obey Hill's new yield criterion and its associated flow rule. A formulation of initial guess generation for the displacement field is derived by using the nonlinear elastic FEM. A method of contact treatment is proposed in which the skew boundary condition for arbitrarily shaped tools is successively used during iteration. In order to verify the validity of the developed method, plane-strain drawing with tools in analytic expression and with arbitrarily shaped tools is analyzed and compared with the published results. The comparison shows that the present method can be effectively used in the analysis of plane-strain sheet metal forming and thus provides the basis of approximate sectional analysis of panel-like sheet forming.

• Journal of the Korean Society for Precision Engineering
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• v.11 no.1
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• pp.129-137
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• 1994

A rigid-viscoplastic finite element method has been used for modeling superplastic stretch/blow process design to improve thickness distribution. Punch velocity-time relationship of the stretch forming and pressure-time cycle of the blow forming for a given strain rate are calculated. A superplastic material is assumed to be isotropic and a plane-strain line element based on membrane approximation is employed for the formulation. The effects of the width, corner radius and height of the punch during stretch forming are examined for the final thickness distribution, and the process design to improve thickness distribution can be established.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1995.10a
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• pp.60-63
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• 1995

The behavior of the work materials in the chip-tool interface in extremely high strain rates and temperatures is more that of viscous liquids than that of normal solid metals. In these circumstances the principles of fluid mechanics can be invoked to describe the metal flow in the neighborhood of the cutting edge. In the present paper an Eulerian finite element model is presented that simulates metal flow in the vicinity of the cutting edge when machining a low carbon steel with carbide cutting tool. The work material is assumed to obey visco-plastic (Bingham solid) constitutive law and Von Mises criterion. Heat generation is included in the model, assuming adiabatic conditions within each element. the mechanical and thermal properties of the work material are accepted to vary with the temperature. The model is based on the virtual work-stream function formulation, emphasis is given on analyzing the formation of the stagnant metal zone ahead of the cutting edge. The model predicts flow field characteristics such as material velocity effective stress and strain-rate distributions as well as built-up layer configuration

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.760-763
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• 2011

본 논문의 목적은 효율적인 3절점 판 유한요소를 개발하는 것이다. Hellinger-Reissner 범함수에 근거한 혼합정식화(mixed formulation)를 사용한다. 잠김현상을 일으키는 전단변형률장을 독립적으로 분리한 후, MITC(Mixed Interpolation of Tensorial Components)방법을 이용하여 대체전단변형률장(assumed transverse shear strain field)을 구성한다. 추가적으로 회전된 반변기저벡터(contravariant base vector)로 정의된 근사전단변형률장(approximated transverse shear strain field)에 미지수(unknowns)를 도입하여 혼합정식화를 완성시키고 정적응축(static condensation)을 통해 최종 강성행렬을 구성한다. 거짓영에너지모드시험(spurious zero energy mode test), 조각시험(patch test), 등방성시험(isotropic test) 등을 실시하였으며, 4변 완전구속 정사각형 판 구조물과 60도 기울어진 단순지지 판 구조물 등 예제들을 해석하여 MITC3판 유한요소와 수렴성능을 비교하였다.