• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.11
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• pp.1862-1870
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• 1997

A fast and precise technique to measure 3-dimensional coordinates of an object is proposed. It is essential to take the 3-dimensional measurements of the object in design and inspection. Using this developed system a surface model of a complex shape can be constructed. 3-dimensional world coordinates are projected onto a camera plane by the perspective transformation, which plays an important role in this measurement system. According to the shape of the object two measuring methods are proposed. One is rotation of an object and the other is translation of measuring unit. Measuring speed depending on image processing time is obtained as 200 points per second. Measurement resolution i sexperimented by two parameters among others; the angle between the laser beam plane and the camera, and the distance between the camera and the object. As a result of these experiments, it was found that measurement resolution ranges from 0.3mm to 1.0mm. This constructed surface model could be used in manufacturing tools such as rapid prototyping machine.

• Korean Journal of Materials Research
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• v.2 no.6
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• pp.436-442
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• 1992

When $N_2$was used as shielding gas during the formation of Ti surface-alloyed layer by irradiation of $CO_2$laser beam on steel, TiN and F$e_2$Ti were formed regardness of carbon-content in steel. When Ti content was increased in low carbon-content steel, formation of martensitic structure was suppressed due to increase of critical cooling rate for martensitic transformation. In case of high-carbon steel, even though Ti content was about 1.5% in alloyed layer, hardness was increased by formation of martensitic structure instead of ferrite. In addition to that structure, hardness was incrreased further by precipitation of TiC in Ti alloyed-layer of high carbon-steel.

• Korean Journal of Optics and Photonics
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• v.15 no.1
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• pp.46-50
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• 2004

Images were acquired by the modulation of terahertz electromagnetic signals and compared by modulation frequencies. For the real-time acquisition of images a fast scanning method has been adopted utilizing a galvanometer. The acquired time domain waveforms were transformed into frequency domain data by fast Fourier transformations (FFT). We chose some frequency components to compare the resolution of images. The beam profiles at the focal position were measured by a knife-edge technique. Beam diameter was shown to decrease as the frequency increased. By scanning one- and two-dimensional samples a significant image enhancement was observed with the frequency increment. A nondesouctive imaging system using ㎔ electromagnetic pulses was also demonstrated.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.1218-1221
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• 2004

Bi2212 superconducting thin films fabricated by using the ion Beam Sputtering Method. As a result, although the composition of Bi2212 was set up, the phase of Bi2201, Bi2212 and Bi2223 was formed. The formation area of these stable phases is indicated as inclined line in the direction of the right lower end from the Arrhenius plot of the substrate temperature-oxidation gas pressure, and are distributed in very small area. The activation energy for the phase transformation from the Bi2201 to the Bi2212 is estimated in terms of the Avrami equation.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2001.11a
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• pp.21-27
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• 2001

Springs are widely utilized in machine element. To find out stiffness of frustum-shaped coil spring, the space beam theory using the finite element method is adopted in this paper In three dimensional space, a space frame element is a straight bar of uniform cross section which is capable of resisting axial forces, bending moments about two principal axes in the plane of its cross section and twisting moment about its centroidal axis. The corresponding displacement degrees of freedom are twelve. To find out load vector of coil spring subjected to distributed compression, principle of virtual work is adapted The displacements of nodal points due to small increment of force are calculated by the finite element method and the calculated nodal displacements are added to coordinates of nodal points. The new stiffness matrix of the system using the new coordinates of nodal points is adopted to calculate the another increments of nodal displacements, that is, the step by step method is used in this paper. The results of the finite element method are fairly well agreed with those of various experiments. Using MATLAB program developed in this paper, spring constants and stresses can be predicted by input of few factors.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.7 s.178
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• pp.1863-1870
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• 2000

When an impact stress is applied on the external boundary of double cantilever beam of orthotropic material which crack length is greater than specimen hight and anistropic ratio is very high, dyna mic energy release rate is derived, and the relationship between dynamic energy release rate and crack propagating velocity is studied. Dynamic energy release rate to static energy release rate is decreased with increasment of crack propagating velocity. The relationships between dynamic energy release rate and vertical strain have a similar pattern with those between static energy release rate and vertical strain. When normalized time(Cstla) is greater than or equal to 2, dynamic energy release rate approaches to a constant value.

• 정보저장시스템학회:학술대회논문집
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• 2005.10a
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• pp.32-37
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• 2005

We developed a numerical simulator in order to study the Super-RENS/ROM (Super REsolution Near-Field Structure, Read Only Memory) using 3-dimensional FDTD (finite difference time domain) method. The simulation can be performed by three steps. In the first step, we utilized the vector-diffraction theory to calculate the characteristics of incident laser beam from the object-lens to the surface of the disk. At the second step, we fed the calculated result as an input for the main FDTD simulations on the optical layers in the disk structure. After performed the FDTD simulations, we took near-to-far field transformation for the reflected signal, from the surface of the disk to the detector. Finally, we can get reflected signal at the photo-diode. Using this developed simulator, we were able to study about the reading signal from various disk structures as a function of a laser beam position. We calculated reading signals for various pit sizes for Super-ROM structure, and it is found that the simple optical diffraction theory can not explain the reading mechanism of Super-ROM, and more complicated temperature dependent physics must be involved.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.56.1-56.1
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• 2012

The microstructures and mechanical properties of Co-29Cr-6Mo alloy with C and N additions, produced by additive manufacturing using electron beam melting (EBM) method, were studied using X-ray diffraction, electron back scatter diffraction, transmission electron microscope, Vickers hardness tests, and tensile tests, focusing on the influences on the build direction and the various heat treatments after build. It is found that the microstructures for the as built specimens were changed from columnar to equiaxed grain structure with average grain size of approximately $10-20{\mu}m$ due to the heat treatment employing the reverse transformation from a lamellar (hcp + $Cr_2N$) phase to an fcc. Our results will contribute to the development of biomedical Ni-free Co-Cr-Mo-N-C alloys, produced by EBM method, with refined grain size and good mechanical properties, without requiring any hot workings.

• Bulletin of the Society of Naval Architects of Korea
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• v.12 no.2
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• pp.3-12
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• 1975

As for two dimensional added mass coefficients for straight framed hull forms in a free surface of an ideal fluid, theoretical calculations by F.M. Lewis, vertical, K. Wendel, J.H. Hwang, and etc. are available; vertical modes of rectangular and triangle sections by Lewis, vertical, horizontal and torsional models of rectangular and triangle section by Wendel, and systematical calculations for vertical modes of single chine forms by Hwang. In this paper, employing the conformal transformation by which a unit circle and its exterior region can conformally mapped to a polygon and its exterior region, the author calculated two dimensional added inertia coefficients systematically for straight framed sections with single chine in horizontal and torsional modes of vibrations. As the results, it was found that sloping side angle is an important factor measuring the magnitude of two dimensional added inertia coefficient for a set of given values of the sectional area coefficient and the beam-draft ratio. To grasp it cleary in physical sense, pressure distributions are investigated for some typical section contours. The numerical results are presented graphically in the form of two dimensional added sectional area coefficients with beam-draft ratios and sloping side angles as parameters, so that the data may conveniently utilized for estimation of the added inertia coefficients based on a three parameter technique.

• Structural Engineering and Mechanics
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• v.11 no.4
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• pp.423-442
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• 2001

This paper presents a method of elastic-plastic analysis for planar steel frames that provides the accuracy of distributed plasticity methods with the computational efficiency that is greater than that of distributed plasticity methods but less than that of plastic-hinge based methods. This method accounts for the effect of spread of plasticity accurately without discretization through the cross-section of a beam-column element, which is achieved by the following procedures. First, nonlinear equations describing the relationships between generalized stresses and strains of the cross-section are derived analytically. Next, nonlinear force-deformation relationships for the beam-column element are obtained through lengthwise integration of the generalized strains. Elastic-plastic flexibility coefficients are then calculated by differentiating the above element force-deformation relationships. Finally, an elastic-plastic stiffness matrix is obtained by making use of the flexibility-stiffness transformation. Adding the conventional geometric stiffness matrix to the elastic-plastic stiffness matrix results in the tangent stiffness matrix, which can readily be used to evaluate the load carrying capacity of steel frames following standard nonlinear analysis procedures. The accuracy of the proposed method is verified by several examples that are sensitive to the effect of spread of plasticity.