• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.6
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• pp.1365-1373
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• 1994

Elasto-dynamic deformation of flexible linkage mechanism was analyzed using the finite element method. A computer program was constructed and applied to analyze a specific crank-level 4-bar mechanism, in which the elasto-dynamic deformation of the mechanism system was obtained using mode superposition method in the case of constant input speed and the effect of geometric stiffness on the mechanism is included. Experimental verification of numerical results was conducted by measuring the elasto-dynamic deformation of mid-points of coupler and lever for the 4-bar lingkage mechanism using high speed camera and image data processing systeem. For the elasto-dynamic deformation at the lever mid-point, the numerical results including geometric stiffness almost agree with the experimental ones. However, the numerical results excluding geometric stiffness good agree with the experimental ones at the couper mid-point.

• Transactions of Materials Processing
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• v.16 no.6
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• pp.473-478
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• 2007

In this study, a deformation mechanism map of metallic nanocrystalline materials(NCMs) using the phase mixture model is proposed. It is based on recent modeling that appears to provide a conclusive description of the phenomenology and the mechanisms underlying the mechanical properties of NCMs. The proposed models adopted the concept of a 'phase mixture' in which the grain interior and the grain boundaries are treated as separate phases. The volume fraction of this grain boundary 'phase' may be quite appreciable in a NCM. Based on the theoretical model that provides an adequate description of the grain size dependence of plasticity covering all grain size range from coarse down to the nanoscale, the tensile deformation response of NCMs, especially focusing on the deformation mechanisms was investigated. The deformation mechanism map is newly proposed with axes of strain rate, grain size and temperature.

• Journal of the Korean Ceramic Society
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• v.33 no.6
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• pp.718-724
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• 1996

Deformation mechanism map of Langdon-Mohammed type for YBa2Cu3O7-x superconducting ceramic was constructed by considering mechanisms of Nabarro-Herring Coble and powder-law creep and grain boundary sliding (GBS) with an accommodation by grain boundary diffusion. The map was found consistent with experi-mental results not only of the creep the also of the superplastic deformation. It showed the transition from interface reaction-controlled to the grain boundary diffusion-controlled GBS mechanism at about 1 ${\mu}{\textrm}{m}$ grain size and 100 MPa flow stress in agreement with the experimental results.

• International Journal of Korean Welding Society
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• v.3 no.2
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• pp.7-14
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• 2003

During the manufacture of a ship, longitudinal deformation is produced by fillet welding on the Built­Up beam used to improve the longitudinal strength of a ship. This deformation needs a correcting process separate from a manufacture process and decreases productivity and quality. This deformation is caused by welding moment, which is the value multiplied the shrinking force due to welding by the distance from the neutral axis on a cross section of Built­Up beam. This deformation can be offset by generating a moment which is the same magnitude with and is located in an opposite direction to the welding moment on web plate by induction heating. Accordingly, this study clarifies the creation mechanism of the longitudinal deformation on Built­Up beam with FEM analysis and presents the preventative method of this deformation by induction heating basing the mechanism and verifies its validity through analysis and experiments. The induction heating used here is performed by deciding its location and quantity with experiments and simple equations and by applying them to a real structure.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.413-417
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• 2004

Recent experiments have shown the 'size effects' in micro/nano scale. But the classical plasticity theories can not predict these size dependent deformation behaviors because their constitutive models have no characteristic material length scale. The Mechanism - based Strain Gradient(MSG) plasticity is proposed to analyze the non-uniform deformation behavior in micro/nano scale. The MSG plasticity is a multi-scale analysis connecting macro-scale deformation of the Statistically Stored Dislocation(SSD) and Geometrically Necessary Dislocation(GND) to the meso-scale deformation using the strain gradient. In this research we present a study of nano-indentation by the MSG plasticity. Using W. D. Nix and H. Gao s model, the analytic solution(including depth dependence of hardness) is obtained for the nano indentation , and furthermore it validated by the experiments.

• Structural Engineering and Mechanics
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• v.42 no.6
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• pp.883-897
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• 2012

Cold-formed channel sections are used in a variety of applications in which they are required to absorb deformation energy. This paper investigates the collapse behaviour and energy absorption capability of cold-formed steel channels with flange edge stiffeners under large deformation major-axis bending. The Yield Line Mechanism technique is applied using the energy method, and based upon measured spatial plastic collapse mechanisms from experiments. Analytical solutions for the collapse curve and in-plane rotation capacity are developed, and used to model the large deformation behaviour and energy absorption. The analytical results are shown to compare well with experimental values. Due to the complexities of the yield line model of the collapse mechanism, a simplified procedure to calculate the energy absorbed by channel sections under large bending deformation is developed and also shown to compare well with the experiments.

• Structural Engineering and Mechanics
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• v.52 no.6
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• pp.1085-1098
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• 2014

Plastic mechanism analysis of structures subjected to large deformation has long been used in order to determine collapse mechanisms of steel structures, and the energy absorbed in plastic deformation during such collapses. In this paper the technique is applied to vehicle roof structures that undergo large plastic deformation as a result of rollover crashes. The components of such roof structures are typically steel spot-welded hat-type sections. Ten different deformation mechanisms are defined from investigations of real-world rollover crashes, and an analytical technique to determine the plastic collapse load and energy absorption of such mechanisms is determined. The procedure is presented in a generic manner, such that it may be applied to any vehicle structure undergoing a rollover induced collapse. The procedure is applied to an exemplar vehicle, in order to demonstrate its application in determining the energy absorbed in the deformation of the identified collapse mechanisms. The procedure will be useful to forensic crash reconstructionists, in order to accurately determine the initial travel velocity of a vehicle that has undergone a rollover and for which the post-crash vehicle deformation is known. It may also be used to perform analytical studies of the collapse resistance of vehicle roof structures for optimisation purposes, which is also demonstrated with an analysis of the effect of varying the geometric and material properties of the roof structure components of the exemplar vehicle.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.4
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• pp.737-752
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• 1992

Analysis of elasto-dynamic deformation of flexible linkage mechanism is conducted using the finite element method. The equations of motion of the system are derived from the static structural problem in which dynamic inertia, gravitational and driving forces are treated as external loads. Linear spring model is included in the formulation of equation of motions to represent the effects of deformation of elastic bearings of revolute joints on the system behavior. A computer program is constructed and applied to analyze a specific crank-lever 4-bar mechanism. The algorithm of the program is as follows. First, the natural frequencies and the mode shapes of the system are calculated by solving the eigenproblem of the mechanism system which can be considered as a static structure by assuming the input shaft (crank shaft) to be fixed at any given configuration of mechanism. And finally, the elasto-dynamic deformation of the whole system is obtained using mode superposition method for the case of constant input speed. The effect of geometric stiffness on the mechamism is included in the program with the axial forces of links obtained through the quasi-static displacement analysis. It is found that the geometric stiffness exerts an important effect upon the elasto-dynamic behavior of the flexible linkage mechanism. Elastic deformation of bearing lowers the natural frequencies of the system, resulting smaller elastic displacement at the mid-point of the links and bigger elestic displacement at the ends of the links than rigid bearing. The above investigation of flexible linkage mechanism shows that the effects of the elastic deformation of bearing on the mechanism should be considered to design the mechanism which satisfies more preciously the purpose and the condition of design.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.410-415
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• 2004

Molecular dynamics simulations of nanoimprint lithography in which a stamp with patterns is pressed onto amorphous poly-(methylmethacrylate) (PMMA) surface are performed to study the deformation of polymer. Force fields including bond, angle, torsion, inversion, van der Waals and electrostatic potential are used to describe the intermolecular and intramolecular force of PMMA molecules and stamp. Periodic boundary condition is used in horizontal direction and $Nos\acute{e}$-Hoover thermostat is used to control the system temperature. As the simulation results, the adhesion forces between stamp and polymer are calculated and the mechanism of deformation are investigated. The effects of the adhesion force and friction force on the polymer deformation are also studied to analyze the pattern transfer in nanoimprint lithography. The mechanism of polymer deformation is investigated by means of inspecting the indentation process, molecular configurational properties, and molecular configurational energies.

• Journal of Welding and Joining
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• v.23 no.3
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• pp.47-53
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• 2005

Longitudinal deformation is produced by fillet welding during the fabrication of built-up beams and decreases productivity and quality because it needs an extra correcting process. The deformation is caused by welding moment, which is the value multiplied the welding shrinking farce by the distance from the neutral axis. This welding moment can be offset by generating a moment in the same magnitude and in an opposite direction by induction heating. The location and quantity of the induction heating are decided via experiments and simple equations. This study, first, clarifies the creation mechanism of the longitudinal deformation with FEM analysis. Then, we presents the preventive method of this deformation by induction heating basing on the mechanism and verifies its validity through analysis and experiments.