• 한국광학회:학술대회논문집
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• 한국광학회 1989년도 제4회 파동 및 레이저 학술발표회 4th Conference on Waves and lasers 논문집 - 한국광학회
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• pp.81-84
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• 1989

EHZP is a kind of holographic optical element, which is generated by the interference of two divergent spherical waves from point sources on the same axis. It has the spherical aberration that the focal power increases as the radial distance r increases. By using this property, optimal design of EHZP was performed for f-$\theta$ lens. As the result of optimization, the f-$\theta$ condition and the field flattening condition were well satisfied when EHZP has f0=0.803f, faR=4.076f, 1=0.406f. It was assumed for calculation of field flattening condition that the incident wave was a plane wave with the diameter of 1mm.

• 대한조선학회논문집
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• 제45권4호
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• pp.417-425
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• 2008

In the line heating process, only angular distortion whose direction is perpendicular to that of a heating path is expected. However, it is observed that a deformation is induced in the direction of the heating line. Because of this, during forming a saddle type plate we experience unfavorable deformations in the unintended direction. In this paper we discuss the unwanted distortion in the manufacturing process by analyzing intermediate plates of saddle type during fabrication. For this analysis we consider the longitudinal and transversal directions separately and use the bending strain for the analysis.

• Journal of Welding and Joining
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• 제29권1호
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• pp.85-89
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• 2011

Waste water is disposed to sewage disposal plant by underground PE double wall pipes. Various processes have been introduced to join PE pipes, but most of these methods have many disadvantages such as costs, lack of reliability and difficulties in joining, etc. Recently butt welding has been paid much attention to joint PE pipes as this process has many advantages such as cost, safety and reliability. In this study, newly developed heat plate, a patent-pending heat plate with a groove, was used to butt-weld PE double wall pipes with different misalignment gaps to simulate real underground conditions, and the butt welding temperature of PE pipe was determined by thermal analysis (Thermal Gravimetric Analysis, Differential Scanning Calorimetry and Dynamic Mechanical Analysis). The resulting joining characteristics of double wall pipes were compared with those from a conventional heat plate, in terms of stiffness, flattening and leakage tests. The results from the stiffness and flattening test showed that there were no big differences between the butt-welded joints made from these two plates. From the leakage test, although PE pipes welded with a conventional heat plate did leak below the required test conditions (10 min. at 0.75kgf/cm2), the pipes welded with a patent-pending grooved heat plate did not show any leakage even at a pressure 1.5 times higher than the required conditions. It was noted that by utilizing a grooved heat plate more complete fusion at the pipe joints could be obtained, which in turn induced a high quality joints.

• 한국기계가공학회지
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• 제14권3호
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• pp.149-154
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• 2015

This study has focused on the deburring technology of a vacuum plate for MLCC lamination using electrolytic in-process dressing (ELID) grinding, and the magnetic-assisted polishing (MAP) process. The surface of the vacuum plate has many micro-holes for vacuum suction. They are easily blocked by the burrs created in the surface-flattening process, such as the conventional grinding process. In this study, the MAP process, the ELID grinding process, and an ultrasonic vibration table are examined to remove the micro-burrs that lead to the blockage of the holes. In the results of the experiments, the MAP process and ELID grinding technology showed significant improvements of surface roughness and deburring performance.

• 한국CDE학회논문집
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• 제11권3호
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• pp.157-163
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• 2006

Surfaces of many engineering structures, especially, those of ships are commonly made out of either single- or double-curved surfaces to meet functional requirements. The first step in the fabrication process of a three-dimensional design surface is unfolding or flattening the surface, otherwise known as planar development, so that manufacturers can determine the initial flat plate which is required to form the design shape. In this paper, an algorithm for optimal approximated development of a general curved surface, including both single- and double-curved surfaces, is established by minimizing the strain energy of deformation from its planar development to the design surface. The unfolding process is formulated into a constrained nonlinear programming problem, based on the deformation theory and finite element. Constraints are subjected to the characteristics of the fabrication method. And the design surface, or the curved shell plate is subdivided by automatic mesh generation.

• 소성∙가공
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• 제14권1호
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• pp.43-48
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• 2005

The production of metal strip with uniform thickness and flatness are two important problems associated thin strip rolling. The thickness and flatness of strip are affected by the flattening of contact surface between strip and roll, the elastic recovery and the bending of roll. Especially, the flatness of the strip is greatly affected by bending deflection of roll. The roll must be designed considered the elastic deformation of roll. This study describes the measurement of thickness and flatness of strip and shows the crown roll for producing flat strip. But it is difficult to produce the crown roller. The cross rolling that is a simple method which can produce the flat strip is introduced and it is found the optimal cross angle for improvement of flatness of plate. These problems are solved by the MARC code on the basis of elastic-plastic material and the updated Lagrangian formulation.

• 한국CDE학회논문집
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• 제11권5호
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• pp.344-350
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• 2006

A method for extracting material information on sheet metal parts from an assembly model is proposed. In order to estimate the cost and order the required sheet metals, their outline profiles, thicknesses, quantities, and etc. are needed. The proposed method consists of two steps: First, sheet metal parts are selected through a feature recognition process from an assembly model. Then, some geometric information for the parts is calculated. In the later step a flattening process of bent parts is included. The method is implemented on a commercial CAD/CAM system Unigraphics with API routines and applied to steam turbine generators and large scale boilers.

• Steel and Composite Structures
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• 제38권2호
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• pp.151-164
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• 2021

During the pipe forming process, a steel plate undergoes inelastic behavior multiple times under a load condition repeating tension and compression in the circumferential direction. It derives local reduction or increase of yield strength within the thickness of steel pipes by the plastic hardening and Bauschinger effect. In this study, a combined hardening model is proposed to effectively predict variations of yield strength in the circumferential direction of API-X65 and X70 steel pipes with relatively low t/D ratio during the forming process, which is expected to experience accumulated plastic strain of 2~3%, the typical Lüder band range in a low-carbon steel. Cyclic tensile tests of API-X65 and X70 steels were performed, and the parameters of the proposed model for the steels were calibrated using the test results. Bending-flattening tests to simulate repeated tension and compression during pipe forming were followed for API-X65 and X70 steels, and the results were compared with those by the proposed model and Zou et al. (2016), in order to verify the process of material model calibration based on tension-compression cyclic test, and the accuracy of the proposed model. Finally, parametric analysis for the yield strength of the steel plate in the circumferential direction of UOE pipe was conducted to investigate the effects of t/D and expansion ratios after O-forming on the yield strength. The results confirmed that the model by Zou et al. (2016) underestimated the yield strength of steel pipe with relatively low t/D ratio, and the parametric analysis showed that the t/D and expansion ratio have a significant impact on the strength of steel pipe.

• 대한구순구개열학회지
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• 제10권2호
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• pp.67-74
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• 2007

After Tennison introduced a triangular flap method which, for the first time, preserved the Cupid's bow, Randall gave this method a sound mathematical basis. This method is also called as an inferior triangular cheiloplasty which is characterized by making a small triangular flap from the lateral border of cleft destined to be fitted into an incision on the medial side of cleft. He postulated that the height obtained was equal to the sum of the median of the two triangles used in the cheiloplasty. Using this technique, a 22 month-old male patient with incomplete unilateral cleft lip was corrected primarily. The deviation of the columella and flattening of the nostril on the cleft side were minimal. The operation was done under general anesthesia and patient was healed uneventfully. We tried to improve the symmetry and esthetic feature of philtrum, nostril sill, alar-facial groove, preventing the notch formation on the nostril floor, and to reconstruct the muscle sling in the upper part of lip. The shape of Cupid's bow was restored, and the symmetry of columella was regained as a result. In summary, the inferior triangular cheiloplasty is effective to correct the primary unilateral cleft lip, results in the restoration of favorable anatomy and function.

• Tribology and Lubricants
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• 제38권1호
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• pp.15-21
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• 2022

Diamond reinforced Cr-based coating has been proposed as wear-resistant materials. In this study, the friction and wear characteristics of diamond reinforced Cr-based coating are experimentally assessed. The experiments are performed using a pin-on-reciprocating plate tribo-tester under various normal forces with boundary lubrication. The stainless-steel ball is used as a counter material. Prior to the experiments, mechanical properties such as elastic modulus and hardness are determined using nanoscale instrumented indentation. The hardness of the specimen is further determined using a Vickers hardness tester. The specimens before and after the experiments are carefully observed using a confocal microscope to understand the wear characteristics. In addition, the wear volume and wear rate of the specimens are determined based on the confocal microscope data. The results show that the friction coefficients are 0.096-0.100 under 20-40 N normal forces. Furthermore, the wear rates of the diamond reinforced Cr-based coating and the stainless steel ball under 20-40 N normal forces are found to be 12.8 × 10^-8 mm³/(Nm)-15.5 × 10^-8 mm³/(Nm) and 1.9 × 10^-8 mm³/(Nm)-3.9 × 10^-8 mm³/(Nm), respectively. However, the effect of the normal force on wear rates is not clearly observed, which may be associated with the flattening of the ball. The results of the study may be useful for the tribological applicability of diamond reinforced Cr-based coating as wear-resistant materials.