• Design & Manufacturing
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• v.7 no.1
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• pp.55-59
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• 2013

A Light Emitting Diode(LED) is a semiconductor device which converts electricity into light. LEDs are widely used in a field of illumination, LCD(Liquid Crystal Display) backlight, mobile signals because they have several merits, such as low power consumption, long lifetime, high brightness, fast response, environment friendly. In general, LEDs production does die bonding and wire bonding on board, and do silicon and phosphor dispensing to protect LED chip and improve brightness. Then lens molding process is performed using mixed liquid silicon rubber(LSR) by resin and hardener. A mixture of resin and hardener affect the optical characteristics of the LED lens. In this paper, computational design of static mixer was performed for mixing of liquid silicon. To evaluate characteristic of mixing efficiency, finite element model of static mixer was generated, and fluidic analysis was performed according to length of mixing element. Finally, optimal condition of length of mixing element was applied to static mixer from result of fluidic analysis.

• Journal of the Korean Society of Safety
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• v.19 no.4 s.68
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• pp.42-47
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• 2004

In this paper, we analyzed on the characteristics of the stranded wire disconnected by repeated stress. The stranded wires that were used in the experiment are PVC insulated flexible cords(VCTFK: Vinyl Insulated Vinyl Cabtyre Cord Flat-type) of $0.75mm^2,\;1.25mm^2,\;and\;2.0mm^2$. They are used to connect the load in low voltage. The stranded wires disconnected by repeated stress were magnified with optical microscope. Using X-ray, the disconnected wire were photo-graphed. we compared mechanical characteristics of the stranded wire between disconnected tendency and allowable current. On the mechanical strength of vinyl cap tire ellipse type cords under bending stress, VCTFK of $1.25mm^2$ was the strongest of them. When it was bent $826.3\pm7$ times, it appeared the disconnected tendency that element wires of VCTFK of $1.25mm^2$ are more about 1.67 times than element wires of VCTFK of $0.75mm^2$. In mechanical strength, VCTFK of $1.25mm^2$ is higher about 1.7 times than VCTFK of $0.75mm^2$. Therefore, we found out that mechanical strength was higher, when the wire had a lot of element wires. In comparison with bending stress, VCTFK of $1.25mm^2$ is the strongest among samples, and it is the most useful in wires of movable type.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.437-441
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• 2001

This paper describes the construction of a circular polariscope. Generally, a circular polariscope contains four optical elements and a light source. The first element following the light source is called the polarizer. It converts the ordinary light into plane-polarized light. The second element is a quarter wave plate which converts the plane-polarized light into circularly polarized light. Following the quarter wave plate, a specimen made of transparent photoelastic material is located in a loading device. The second quarter wave plate is set and the last element is the analyzer. These polarizing elements, two quarter wave plates and two polarizing filters, were purchased from the USA. Frames and other structures for holding polarizing filters were machined and assembled to be rotated. Light box, which include four incandescent lamps and two sodium-vapor lamps, was made. In order to proof the function of the newly built polariscope, Tardy compensation test was applied to a rectangular shaped specimen made of poly-carbonate material (PSM1). The error of the fringe constant, which was measured by the newly built polariscope, was within 4.4 percent compared to the standard value of this material. It is possible to make a good quality of polariscope if accurate polarizing filters will be used.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07a
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• pp.464-467
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• 2003

In this paper, we analyzed on the characteristics of the stranded wire disconnected by bending stress. The stranded wire that used in the experiment are PVC insulated flexible cords(VCTFK) of $0.75mm^2,\;1.25mm^2,\;and\;2.0mm^2$. They are used to connect the load in low voltage. The stranded wires disconnected by bending stress were magnified with optical microscope. Using X-ray, the disconnected wire were photographed. we compared mechanical characteristics of the stranded wire between disconnected tendency and allowable current. On the mechanical strength of vinyl captyre ellipse type cords under bending stress, $1.25mm^2$ VCTFK was the strongest of them. When it was bended $826.3{\pm}7\;times$, it appeared the disconnected tendency that element wires of $1.25mm^2$ VCTFK are more about 1.67 times than element wires of $0.75mm^2$ VCTFK. In mechanical strength, $1.25mm^2$ VCTFK is higher about 1.7 times than $0.75mm^2$ VCTFK. Therefore, we found out that mechanical strength will be higher, if element wire is a lot. In comparison with bending stress, $1.25mm^2$ VCTFK is the strongest among samples, and then it is the most useful in wires of movable type.

• Journal of the Korean Society of Safety
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• v.35 no.5
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• pp.1-8
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• 2020

Mobile elevating work platforms (MEWPs) consist of a work platform, extending structure, and chassis, and are used to move persons to working positions. MEWPs are useful but are composed of pieces of equipment, and accidents do occur owing to equipment defects. Among these defects, accidents caused by the fracture of bolts fixed to the extension structure and swing system are increasing. This paper presents a failure analysis of the fixing bolts of MEWP. Standard procedure for failure analysis was employed in this investigation. Visual inspection, chemical analysis, tensile strength measurement, microstructural characterization, fractography analysis by Optical Microscope(OM) and Scanning Electron Microscopy(SEM), and finite element analysis (FEA) were used to analyze the failure of the fixing bolts. Using this failure analysis approach, we found the root cause of failure and proposed a means for solving this type of failure in the future. First, the chemical composition of the fixing bolt is obtained by a spectroscopy chemical analysis method, which determined that the chemical composition matched the required standard. The tensile test showed that the tensile and yield strengths were within the required capacity. The stress analysis was carried out at five different boom angles, and it was determined that the fixing bolt of MEWP can withstand the loads at all the boom angles. The outcomes of the fatigue analysis revealed that the fixing bolt fails before reaching the design requirements. The results of the fatigue analysis showed primarily that the failure of the fixing bolt was due to fatigue. A visual inspection of the fractured section of the fixing bolt also confirmed the fatigue failure. We propose a method to prevent failure of the fixing bolt of the MEWP from four different standpoints: the manufacturer, safety certification authority, safety inspection agency, and owner.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.414-415
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• 2005

A solar cell is an element to transform the solar light energy into the electric energy in a moment. The single crystal element of high quality on which many studies were conducted in the past has a high efficiency of energy transformation, but its price competitiveness is so poor that it has failed to be popularized However, recently, in terms of an environment-friendly alternative energy, studies on applicability of the polycrystal solar cell have been actively under way. Among subject substances for such solar cell, $CuInSe_2$ has several good physical properties so that the greatest attention is paid to it as an optical absorption layer material for a low-cost solar cell of high efficiency. In order to manufacture the $CuInSe_2$ compound thin film, the unit element was deposited by using the sputtering method and the evaporation method and the heat treatment process was used in an electric furnace. Thereby, we intended to get a single-phase $CuInSe_2$ compound thin film.

• The Journal of Korean Academy of Prosthodontics
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• v.41 no.5
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• pp.582-595
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• 2003

Statement of problem : Most posts are metallic, but in response to the need for a post that possesses optical properties compatible with an all-ceramic crown. an esthetic post has been developed. Although there have been many studies about the esthetic post materials, 3-dimensional finite element studies about the stress distribution of them are in rare. Purpose : The purpose of this study is to investigate comparatively the distribution of stresses of the restored, endodontically treated maxillary incisors with the esthetic post materials and the displacement on the cement layer on simulated occlusal loading by using a 3-dimensional finite element analysis model. Material and method : Four 3-dimensional finite element models were constructed in a view of a maxillary central incisor, a post, a core, and the supporting tissues to investigate the stresses in various esthetic posts and cores and the displacement on the cement layer (Model 1 ; Cast gold post and core, Model 2 ; Glass fiber post with composite core, Model 3 ; Zirconia post with composite core. Model 4 ; Zirconia post with ceramic core). Force of 300N was applied to the incisal edge and the cingulum (centric stop point) with the angle of 135-degree to the long axis of the tooth. Results : 1. The stresses and displacement on the incisal edge were higher than on the cingulum 2. The stresses in dentin were the highest in Model 2 (Glass fiber post with composite core), and the second was Model 3, the third Model 1, and the lowest Model 4. 3. The stresses in post and core were the highest in Model 4 (Zirconia post with ceramic core), and the second was Model 1, the third Model 3, and the lowest Model 2. 4. The displacement on the cement layer was the highest in Model 2 (Glass fiber post with composite core), and the second was Model 3, the third Model 1, and the lowest Model 4. Conclusion : When a functional maximum bite force was applied, the distribution of stresses or the esthetic post and core materials and the displacement on the cement layer were a little different. It seems that restoring extensively damaged incisors with esthetic post and core materials would be decided according to the remaining tooth structure.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.05a
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• pp.195-198
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• 2007

The present work focuses on the prediction of birefringence in injection-molded plastic part and its improvement by rapid mold heating. To calculate birefringence, flow-induced residual stress is computed through a fully three-dimensional injection molding analysis. Then the stress-optical law is applied from which the order of birefringence can be evaluated and visualized. The birefringence patterns are predicted for a rectangular plate with a variation of mold temperatures, which shows that the amount of molecular orientation and birefringence level decreases with an increase of mold temperature. The effect of mold temperature on the order of birefringence is also studied for a thin-walled rectangular strip, and compared with experimental measurements. Both predicted and experimental patterns of birefringence are in agreements on the observation that the birefringence level diminishes significantly when the mold temperature is raised to above the glass transition temperature.

• Aerospace Engineering and Technology
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• v.4 no.1
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• pp.108-113
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• 2005

Strucutral and hygrothermal analysis for a composite tube is carried out in this study, that provides critical parameters for the design of a highly dimensionally stable space telescope. Carpet plots for laminate effective engineering constants are generated and used for the best tube lay-ups with high elastic modulus and highly insensitive to thermal and moisture expansion, which is essential for maintaining optical alignment of opto-mechanical system under random force applied during a launch campaign and orbital thermal load. Despace in the longitudinal direction under hygrothermal load of the tubes constructed with the selected lay-ups is calculated for the validation of lay-up designs on the dimensionalstability. Dynamic analysis is also carried out to feature the resonant behaviour. A zig-zag triangular element accurately representing through thickness stress variations for laminated structures is developed in this study and incorporated into the structural and hygrothermal analysis.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.04a
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• pp.41-47
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• 2003

This study is an attempt to understand the birefringence and stress development in an injection molded disk. A computer code was developed to simulate all three stages of the injection molding process - filling, packing and cooling by finite element method. The constitutive equation used here was compressible Leonov model. The PVT relationship was assumed to follow the Tait equation. The flow-induced birefringence was related to the calculated flow stresses through the linear stress-optical law. The predicted birefringence was in good agreement with the experimental results.