• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.1
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• pp.105-112
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• 2002

In recent years, the integrity of reactor Pressure Vessel(RPV) under pressurized thermal shock (PTS) accident has been treated as one of the most critical issues. Under PTS condition, the combination of thermal and mechanical stress by steep temperature gradient and internal pressure causes considerably high tensile stress at the inside of RPV wall. As a result, cracks on inner surface of RPV may experience elastic-plastic behavior which can be characterized by J-integral. In such a case, however, J-integral may possibly lose its vapidity due to the constraint effect. The degree of constraint effect is influenced by the loading mode, crack geometry and material properties. In this paper, in order to investigate the effect of clad thickness and crack geometry on constraint effect, three dimensional finite element analyses were performed for various surface cracks. Total of 27 crack geometries were analyzed and results were presented by a two-parameter characterization based on the J-integral and the f-stress.

• International Journal of Fuzzy Logic and Intelligent Systems
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• v.5 no.2
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• pp.119-123
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• 2005

This paper describes a fuzzy-based system for analyzing the stress intensity factors (SIFs) of three-dimensional (3D) cracks. 3D finite element method(FEM) was used to obtain the SIF for subsurface cracks and surface cracks existing in inhomogeneous materials. A geometry model, i.e. a solid containing one or several 3D cracks is defined. Several distributions of local node density are chosen, and then automatically superposed on one another over the geometry model by using the fuzzy theory. Nodes are generated by the bucketing method, and ten-noded quadratic tetrahedral solid elements are generated by the Delaunay triangulation techniques. The singular elements such that the mid-point nodes near crack front are shifted at the quarter-points, and these are automatically placed along the 3D crack front. The complete FE model is generated, and a stress analysis is performed. The SIFs are calculated using the displacement extrapolation method. The results were compared with those surface cracks in homogeneous materials. Also, this system is applied to analyze cladding effect of surface cracks in inhomogeneous materials.

• Transactions of Materials Processing
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• v.9 no.4
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• pp.404-412
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• 2000

It is desirable to use the square grid analysis with the aid of the stereo vision and image processing techniques in order to automatically measure the surface-strain distribution over a stamped part. But this method has some inherent problems such as the difficulty in enhancement of bad images, the measurement error due to the digital image resolution and the limit of the area that can be measured at a time. Therefore, it is still hard to measure the strain distribution over the entire surface of a medium-or large-sized stamped part even by using an automated strain measurement system. In this study, several methods which enable to solve these problems considerably without losing accuracy and precision In measurement are suggested. The superposition of images that have different high-lightened or damaged part from each other gives much enhanced image. A new algorithm for constructing of the element connectivity from the line-thinned image helps recognize up to 1,000 elements. And the geometry assembling algorithm including the global error minimization makes it possible to measure a large specimen with reliability and efficiency.

• Proceedings of the KIEE Conference
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• 2005.07c
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• pp.2109-2111
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• 2005

The effect of arc like streamer discharge is investigated on the hydrogen generation in the plasma reactor with multineedle - plate electrode geometry and SDR (Plasma reactor using the surface discharge). An additive of the two type (the saw type and the pellet type) was placed under the water surface to investigate the effect of the water surface conditions. The experimental results are compared in case of the reactor with and without an additive on the water surface. The generation of arc streamer discharge is more powerful with increasing applied voltage in the saw type. The maximum hydrogen Production concentration is about 4300 ppm at 74W in the SDR with additive of the saw type. Also, the Energy yield of the SDR (28990 g/kWh, 4300ppm, 74W) is higher than of the multineedle - plate electrode geometry (20892g/kWh, 3300ppm, 77W).

• Composites Research
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• v.33 no.3
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• pp.147-152
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• 2020

In this study, void behavior of composite laminate by local internal pressure gradient due to structural geometry and surface film application condition was experimentally evaluated through fabrication of spar/skin integrated structure specimens. Viscosity comparison and thermal analysis for both carbon fiber prepreg and surface film were conducted and cure characteristic and rate difference were analyzed. 2 types of spar/skin integrated structural specimens were prepared based on different application condition of surface film. Subsequently, those specimens were evaluated through visual surface inspection, non-destructive and destructive inspection. In a specimen #1 with full application of surface film, low pressurized area of composite laminate created by pressure gradient of structural geometry had voids. It exhibited that voids could not be evacuated and were locked in cured laminate by the influence of pre-cured surface film with relatively faster cure rate. In a specimen #2 without surface film, it revealed that all internal voids disappeared in the cured laminate. Therefore, it is verified that surface film acts as barrier film preventing void movement and evacuation during autoclave cure.

• Transactions of Materials Processing
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• v.16 no.7
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• pp.521-529
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• 2007

This paper is concerned with the analysis on the surface expansion of AA 2024 and AA 1100 aluminum alloys in backward extrusion process. Due to heavy surface expansion appeared usually in the backward can extrusion process, the tribological conditions along the interface between the material and the punch land are very severe. In the present study, the surface expansion is analyzed especially under various process conditions. The main goal of this study is to investigate the influence of degree of reduction in height, geometries of punch nose, friction and hardening characteristics of different aluminum alloys on the material flow and thus on the surface expansion on the working material. Two different materials are selected for investigation as model materials and they are AA 2024 and AA 1100 aluminum alloys. The geometrical parameters employed in analysis include punch corner radius and punch nose angle. The geometry of punch follows basically the recommendation of ICFG and some variations of punch geometry are adopted to obtain quantitative information on the effect of geometrical parameters on material flow. Extensive simulation has been conducted by applying the rigid-plastic finite element method to the backward can extrusion process under different geometrical, material, and interface conditions. The simulation results are summarized in terms of surface expansion at different reduction in height, deformation patterns including pressure distributions along the interface between workpiece and punch, comparison of surface expansion between two model materials, geometrical and interfacial parametric effects on surface expansion, and load-stroke relationships.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.251-252
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• 2002

An algorithm has been developed to determine changes in surface topography on asperity level. The software stitches small but detailed images together to create one large image. If such an image is made before and after an experiment, their difference shows a direct 3D view of the changes in micro-geometry, rather than a change in surface parameters. The algorithm is described in detail and illustrated using artificial as well as real surfaces.

• Journal of Institute of Control, Robotics and Systems
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• v.5 no.4
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• pp.481-488
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• 1999

A thermal model based on the chamber geometry of the industry-standard AST SHS200MA rapid thermal processing system has been developed for the study of thermal uniformity and process repeatability thermal model combines radiation energy transfer directly from the tungsten-halogen lamps and the steady-state thermal conducting equations. Because of the difficulties of solving partial differential equation, calculation of wafer temperature was performed by using finite-difference approximation. The proposed thermal model was verified via titanium silicidation experiments. As a result, we can conclude that the thermal model show good estimation of wafer surface temperature distribution.

• Journal of Welding and Joining
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• v.35 no.1
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• pp.16-25
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• 2017

Gas Metal Arc Welding is a widely used process in Industry due to its high productivity and potential to automation. The present study investigates the effects of the welding speed, arc voltage, welding current and shielding gas on the bead geometry for a low-carbon steel. The Response Surface Methodology (RSM) is used to choose an experimental design and perform test runs accordingly in order to produce mathematical models predicting the geometry, the hardness and the heat input of the bead as functions of the welding parameters. The direct and interaction effects of the four welding parameters are represented graphically and allow to determine an optimum set of welding parameters.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2002.04a
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• pp.209-214
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• 2002

Mechanical micro-engineering is an easy and cheap way to fabricate micro-structures. If the application of the conventional machining method using flat-end mill becomes available for the micro-manufacturing process, it will be advanced as an extension of the conventional machining process. In this study, micro-grooves cutting using flat-end mill(($\phi$8) was performed. The characteristics on flat-end milling was investigated to improve machinability of micro-grooves. The experiments were performed according to variations of spindle revolution, depth of cut, and feed rate. Machinability through various cutting conditions was evaluated by surface geometry, tool wear, and cutting force. The results show that micro V-grooves of width(pitch) 29${\mu}{\textrm}{m}$ were acquired by flat-end milling. The maximum and minimum roughness of the wall of grooves was 438 and 67nm, respectively