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임세영(Seyoung Im),최강혁(Kanghyouk Choi) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
In this paper, a finite element analysis of arc-welding processes is presented for large structures. We use an implicit numerical implementation for Leblond’s transformation plasticity constitutive equations, which are widely used in steel-structure welding. Several numerical examples, particularly including a large structure undergoing significant elastic-plastic deformations before welding, are presented to demonstrate the effectiveness of the three-dimensional analysis of welding processes.
B-bar aided edge-based smoothed finite elements of hexahedron type for elasto-plasticity
Son, Youngtak,Im, Seyoung 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.2
<P>The purpose of this study is to perform elastoplastic analysis using an edge-based smoothed finite element of hexahedron type. The edge-based smoothed finite element method has the best performance among the smoothed finite element methods, but has the problem of the volumetric locking phenomenon. Since plastic deformation is an isochoric process, it is accompanied by volumetric locking. In this study, the B-bar approach was introduced in the ESFEM to solve the volumetric locking phenomenon, and to enable elastoplastic analysis. The proposed method was verified to be efficient and accurate by comparison with results from the conventional finite element method.</P>
Kim, Moonhong,Im, Seyoung Elsevier 2017 Computer methods in applied mechanics and engineer Vol.325 No.-
<P><B>Abstract</B></P> <P>An equivalent continuum model for multilayer graphene sheets (MLGSs) and its plate model are developed to analyze the deformation behavior of MLGSs. Hyperelastic material models are introduced for the MLGS continuum model by examining the atomistic structures of MLGSs and obtaining their mechanical properties by means of molecular statics simulations. The MLGS plate model, a structural model for MLGSs, is developed by applying kinematics assumptions to the MLGS continuum model subjected to infinitesimal deformation. Finite element methods (FEM) with the corotational formulation are adopted to analyze the mechanical behavior of MLGSs under small-strain deformation and large rotation conditions. The MLGS plate element passes several basic numerical tests, including patch tests, eigenvalue analyses, and geometrically nonlinear benchmark problems. Finally, the deflections of a plane-strain cantilever and spherical indentations are analyzed by the proposed MLGS plate element and molecular dynamics (MD) simulations. These results show that the MLGS plate element properly represents the deformation behaviors of MLGSs from the atomic scale to the macroscopic continuum scale.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We present a plate finite element able to analyze deformation of MLGSs. </LI> <LI> Interlayer slip and layer deformation are described by kinematics assumptions. </LI> <LI> Corotational formulation is employed for small-strain deformations & large rotations. </LI> <LI> The element is verified as a structural element and a continuum description of MLGSs. </LI> </UL> </P>
(4+n)-noded Moving Least Square(MLS)-based finite elements for mesh gradation
Lim, Jae Hyuk,Im, Seyoung Techno-Press 2007 Structural Engineering and Mechanics, An Int'l Jou Vol.25 No.1
A new class of finite elements is described for dealing with mesh gradation. The approach employs the moving least square (MLS) scheme to devise a class of elements with an arbitrary number of nodal points on the parental domain. This approach generally leads to elements with rational shape functions, which significantly extends the function space of the conventional finite element method. With a special choice of the nodal points and the base functions, the method results in useful elements with polynomial shape functions for which the $C^1$ continuity breaks down across the boundaries between the subdomains comprising one element. Among those, (4 + n)-noded MLS based finite elements possess the generality to be connected with an arbitrary number of linear elements at a side of a given element. It enables us to connect one finite element with a few finite elements without complex remeshing. The effectiveness of the new elements is demonstrated via appropriate numerical examples.
An Investigation on Collapse Behavior of Shear Localization in Elasto-Thermo-Viscoplastic Materials
Hyun-Gyu Kim,Seyoung Im 대한기계학회 2006 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.20 No.12
The stress collapse in the formation of shear bands in elasto-thermo-viscoplatic materials is systematically studied within the framework of one-dimensional formulation via analytical and numerical methods. The elastic energy released in a domain is found to play an important role in the collapse behavior of shear localization. A non-dimensional parameter named the stability indicator is introduced to characterize the collapse behavior, with approximate forms of the incremental governing equations. The stability indicator offers useful information regarding the degree of severity of an abrupt change of deformations during the stress collapse. Numerical experiments are carried out to verify the stability indicator by varying material properties.
Polyhedral elements by means of node/edge‐based smoothed finite element method
Lee, Chan,Kim, Hobeom,Im, Seyoung John Wiley Sons, Ltd 2017 International Journal for Numerical Methods in Eng Vol.110 No.11
<P><B>Summary</B></P><P>The node‐based or edge‐based smoothed finite element method is extended to develop polyhedral elements that are allowed to have an arbitrary number of nodes or faces, and so retain a good geometric adaptability. The strain smoothing technique and implicit shape functions based on the linear point interpolation make the element formulation simple and straightforward. The resulting polyhedral elements are free from the excessive zero‐energy modes and yield a robust solution very much insensitive to mesh distortion. Several numerical examples within the framework of linear elasticity demonstrate the accuracy and convergence behavior. The smoothed finite element method‐based polyhedral elements in general yield solutions of better accuracy and faster convergence rate than those of the conventional finite element methods. Copyright © 2016 John Wiley & Sons, Ltd.</P>