(A)Study on regional feature a nd transition of the costume on the wall paintings of Koguryo tombs

학위논문(박사)--서울대학교 대학원 :의류학과,2003.Docto

Elastic-Plastic Finite Element Analysis of Sheet Metal Forming Processes(II) - Analysis of Metal Forming Processes with Contact Condition -

Based on the formulation which incorporates large deformation and anisotropy, an elastic-plastic finite element code is developed with membrane element to include the contact treatment. For the analysis of the general sheet metal forming process with contact condition, the treatment of contact is considered by employing the successive skew coordinate system. Three kinds of sheet metal forming processes with contact conditions are analyzed; stretching of a square diaphragm with a hemispherical punch, deep drawing of a circular cup and deep drawing of a square cup. Then the computational results are compared with the experiment. The computed loads and the distribution of the thickness strain are in good agreement with the experiment for all cases. However, the computational results of the thickness strain show the effect of bending can not be ignored in the deep drawing process whereas the effect of bending is negligible in stretching

Elastic-Plastic Finite Element Analysis of Sheet Metal Forming Processes(I)-Finite Element Formulation and Analysis of Hydrostatic Bulging-

An incremental formulation incorporating the effect of shape change is derived for non-steady large elastic-plastic deformation of rate-independent anisotropic sheet material. The kinematics of deformation during each step is considered by employing the natural convected coordinate system. From the derived formulation, a finite element code is developed with membrane elements. Hydrostatic bulging of a circular diagram and hydrostatic bulging of a square diaphragm are analyzed in order to check the validity of the present formulation. The computed results are compared with the existing experimental results as well as the results of rigid-plastic FE analysis. The comparison has shown that the computation is in good agreement with the experiment and the rigid-plastic FEM results

Rigid-Plastic Finite Element Analysis of Axi-symmetric Hydroforming with Controlled Pressure

The study is concerned with the analysis of axisymmetric hydroforming with controlled pressure by the rigid-plastic finite element method. The finite element method is employed to obtain the detailed information including the distribution of stresses and strains and geometry changes. Experiments are carried out for hydroforming of cold-rolled steel sheets with the developed CNC hydroforming press which is pressure-controlled according to the fluid pressure vs.-stroke relationship given by the upper bound. Four types of punches are used for the experiments. The computed results are in good agreements with the experimental observation in geometric change and thickness variation. The present analysis permits the prediction of stresses, strains, geometric changes. The effects of Lankford value and workhardening exponent on thickness strains in hydroforming are also discussed. It is thus shown that the present method can be applied to the effective design of axisymmetric hydrooforming processes

A slip line analysis of the ring rolling process using a matrix method

학위논문(석사) - 한국과학기술원 : 생산공학과, 1985.2, [ v, 63 p. ]한국과학기술원 : 생산공학과

A Study on the Shear Deformation Behavior of Inner Structure-Bonded Sheet Metal

In order to improve the quality of the sheared surface in cutting of inner structure bonded sheet metal the cut-off operation is mainly investigated, which is the typical shearing process in sheet metal forming technology. The sandwich sheet metals considered have inner structure which is constructed in the form of crimped expanded metal and woven metal. The inner structure is bonded between solid sheet by resistance welding or adhesive bonding. The shearing process is visualized by the computer vision system installed in front of the cut-off die and the sheared surface is measured and quantitatively compared with the help of the optical microscope after cut-off operation. From test results we found that the influence of sheared position can be observed and explained clearly and this result can be utilized to get the better sheared surface

접촉과 마찰을 고려한 박판성형의 강소성 유한요소해석

학위논문(박사) - 한국과학기술원 : 생산공학과, 1989.8, [ ix, 148 p. ]Process modelling of sheet metal forming with contact is carried out by using the rigid-plastic finite element method based on the membrane theory. The sheet materials are assumed to possess normal anisotropy and to obey Hill``s new yield criterion and its associated flow rule. A variational formulation is derived for the incremental analysis of the nonsteady large deformation of normal anisotropic rigid-plastic sheet metal obeying Hill``s new yield criterion. Geometric nonlinearity is incorporated by using the convected coordinate system and by introducing the asumption about the deformation path. Using the natural convected coordinate system, the numerical efficiency is improved. The corresponding finite element equations are found from the variational equation in order to analyze the sheet metal forming processes. In order to show the validity of the present formulation, hydrostatic bulging of circular and elliptic diaphragms are analyzed. The computational results are shown to be in good agreement with the existing theoretical and experimental results. A systematic method of initial guess generation is devised by using the nonlinear elastic finite element method combined with the proposed contact treatment. An improved method of contact treatment is developed in which skew boundary condition is successively used during iteration. A simple but effective contact algorithm to decide the proper contact region is also suggested. In order to verify the validity of the developed method, axisymmetric stretching is analyzed and compared with the available axisymmetric FEM results. As three-dimensional applications, stretching of a square sheet and deep drawing of a square cup from a circular blank are analyzed. The supporting experiments are also che computational results are compared with the experiments. The comparison shows that the computed results by the proposed method are generally in good agreement with the experiments. It is shown that the present method ca...한국과학기술원 : 생산공학과