• Journal of the Korea Institute of Military Science and Technology
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• v.7 no.1
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• pp.47-58
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• 2004

Loss factors of A356, Mn-Cu alloy and aluminum matrix composites reinforced with $SiC_p$ and Ni-coated graphite particles at various contents have been investigated using clamped-free cantilever beam method. The loss factors of half-power bandwidth of the specimens were measured over a wide range of frequencies from 50 to 3300Hz. Among the specimens, Al-10%$SiC_p$-10%$C_p$ showed the highest loss factor at the mode I, while Mn-Cu alloy showed the highest loss factors at the modes II and III. Consequently, at the mode I the Al-10%$SiC_p$--10%$C_p$ showed the loss factor of 0.00093, which is 2.64 and 1.58 times higher than those of A356 and Mn-Cu alloy, respectively.

• Journal of Korea Foundry Society
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• v.13 no.1
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• pp.62-70
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• 1993

This study presents the effect of applied pressure on the preform deformation during squeeze casting of $Al_2O_3$ short fiber reinforced aluminum alloy (AC8A) metal matrix composites. A preliminary model based on the general beam theory is suggested for the prediction of the preform deformation. Two different commercially available $Al_2O_3$ short fiber (Saffil, Kaowool) were used to study the influence of the fibers on the microstructure and mechanical properties of the squeeze cast $Al/Al_2O_3$ composites. The composites were fabricated with the applied pressure of 75 MPa which was found to be the optimum condition for the squeeze casting of the composites in this study. For the amorphous Kaowool fiber, hard crystalline Mullite phase was formed with heat treatment. Both of amorphous and the crystallized Kaowool fibers were used to fabricate $Al/Al_2O_3$ composites. Microhardness of crystallized Kaowool fiber revealed higher than that of the amorphous Kaowool fiber in the squeeze cast composites. It was also found that the wear resistance of Kaowool fiber reinforced composites increased with the amount of Mullite.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.5
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• pp.337-343
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• 2017

As a shop practice, a strength estimation method for die cast parts is suggested, in which various defects such as pores can be allowed. The equivalent porosity is evaluated by combining the stiffness data from a simple elastic test at the part level during the shop practice and the theoretical stiffness data, which are defect free. A porosity equation is derived from Eshelby's inclusion theory. Then, using the Mori-Tanaka method, the porosity value is used to draw a stress-strain curve for the porous material. In this paper, the Hollomon equation is used to capture the strain hardening effect. This stress-strain curve can be used to estimate the strength of a die cast part with porous defects. An elastoplastic theoretical solution is derived for the three-point bending of a die cast beam by using the plastic hinge method as a reference solution for a part with porous defects.

• Asian-Australasian Journal of Animal Sciences
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• v.19 no.12
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• pp.1737-1741
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• 2006

The aim of this study was to provide basic information to allow improved nutritional management for velvet production by investigating the effects of dietary protein levels on dry matter intake and production and chemical composition of velvet antler in spotted deer (Cervus nippon). Twenty-four spotted deer stags were assigned to 4 unreplicated groups, Control (15% CP in diet, higher dry matter), CP10 (10% CP), CP15 (15% CP) and CP20 (20% CP). The velvet antlers were harvested from each stag on the 55th day after casting of the buttons from the previous set, measured for their size and weight, and the chemical composition of each antler was determined in three sections (top, middle, and base). Dry matter (DMI) and crude protein (CPI) intake were highest (p<0.05) for the Control and increased progressively (p<0.05) with increasing dietary protein level. Although not significant, mean length and girth of the main antler beam tended to be larger in either left or right beam with increasing protein level in the diet, longest in CP20 and shortest in CP10. Velvet antler production was lowest in CP10 and highest in CP20, which differed significantly (p<0.05). Only negligible differences were found between groups in chemical composition. It is concluded that dietary protein clearly influenced dry matter intake and velvet antler production, whereas there was comparatively little effect of dietary protein on chemical composition of antler in spotted deer.

• Journal of Dental Rehabilitation and Applied Science
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• v.32 no.1
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• pp.60-69
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• 2016

Purpose: The objective of this study was to compare the accuracy of digital models from 3 dimentional (3D) optical scanner and cone beam computed tomography (CBCT). Materials and Methods: We obtained digital models from 11 pairs of stone casts using a 3D optical scanner and a CBCT, and compared the accuracy of the models. Results: The error range of average positive distance was 0.059 - 0.117 mm and negative distance was 0.066 - 0.146 mm. Statistically (P < 0.05), average positive distance was larger than $70{\mu}m$ and shorter than $100{\mu}m$, and that of negative distance was larger than $100{\mu}m$ and shorter than $120{\mu}m$. Conclusion: We concluded that the accuracy of digital models generated from CBCT is not appropriate to make final prostheses. However, it may be acceptable for provisional restorations and orthodontic diagnoses with respect to the accuracy of the digitalization.

• The Journal of Korean Academy of Prosthodontics
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• v.37 no.5
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• pp.545-566
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• 1999

The use of pure titanium and titanium alloys have been increased recently in fixed, removable prosthodontics and implant fields as a framework. But when they were used for superstructures of implant or metal framework of removable prosthesis, welding is necessary to reconnect the fracture site to control the casting distortions. To overcome the difficulties in soldering the titanium due to high oxidation property, much effort have been devoted. In this study, some of mechanical properties were compared between pure titanium and Ti-6Al-4V alloy by using after welding, electron beam welding technique and tungsten arc welding. Mechanical properties such as tensile strength, yield strength, elongation and microhardness were measured. And, in order to compare the effect of welding site and surrounding metal tissue according to the welding condition, SEM photographs were taken and element distribution was observed by Wave Dispersion Spectroscopy. Through analyses of the data, following results were obtained; 1. In items such as tensile strength, yield strength and elongation according to the welding techniques of pure titanium, only tungsten arc welded group showed significant lower value than other groups(P<0.05). 2. In items such as tensile strength and yield strength according to the welding techniques of Ti-6Al-4V alloy, control group and tungsten arc welded group showed significant difference among all the groups(P<0.05). 3. Ti-6Al-4V alloy exhibited significantly greater elongation than control group when the laser welding method and electron beam welding method were used, and elongation showed increasing tendency. 4. Pure titanium specimens exhibited increasing tendency of microhardness regardless of the weld-ing technique applied, and especially tungsten arc welded group demonstrated a great increase of microhardness than parent metal. 5. There was no hardness change in laser welded group and electron beam welded group of Ti-6Al-4V alloy, but in tungsten arc welded group, hardness changed greatly from parent metal to weld seam. 6. Through the metallographic examination and scanning electron microscopy, laser welding caused central fusion and recristallizations were formed and tungsten arc welding caused localized fusion to 0.3-0.7mm from the surface.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.4
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• pp.351-356
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• 2009

A dual-mode annular ring antenna for both global positioning system(GPS) and satellite digital multimedia broad-casting(DMB) is designed. The proposed antenna consists of a coupling feed line and four slots on the annular ring patch. The gap between the feed line and the annular ring patch is used for an input impedance matching, and the slot length is used for adjusting the resonant frequency of the $TM_{21}$ mode at the DMB frequency. The antenna was fabricated and measured. The experimental results show that the antenna resonants at the GPS and DMB frequencies with suitable bandwidths, and had a broadside radiation pattern at the GPS band and a conical beam radiation pattern at the DMB band.

• Transactions of the Korean Society of Automotive Engineers
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• v.21 no.4
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• pp.159-165
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• 2013

One of the leading causes of night time automobile accidents is the darkness of surroundings. Headlamps play a critical role in casting light and providing drivers with visibility. Headlamp design and new technology have been developed recently as research has been actively carried out to increase headlamp recognition. This study statistically analyzes irradiation distance using computer simulation by categorizing headlamps applied in domestic automobiles in the last decade by year, light source, form, vehicle type, and height of installation. After analyzing results of irradiation distance, it appears irradiation distance has been increased by approximately 10m in the last decade. This increase in irradiation distance is predicted to decrease night time accidents by allowing more time to recognize potential causes of accidents.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.12
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• pp.142-150
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• 1996

Nowadays, as the development paeiod of new products becomes even shorter, the importance of Rapid Prototyping Technology(RPT) has been rapidly increased. The major application of RPT is an early verification of product designs and quick production of prototypes for testing. Moreover, RPT is applied not only as a second tooling process such as mold making and investment casting but also as a creating some physical structure in medical field. Despite the remarkable progress of RPT, it is required to improve various problems resulting from application such as production time, accuracy and materials. This paper presents a laser scan path generation for accuracy of stereolithographicparts The methodology of laser scan path generation is discussed based on the stereolithography, The procedure of this research is as follows : 1) Input laser scanning conditions such as a laser beam diameter and a laser scanning interval, 2) Reconstruct original contours without self intersecting offset, 3) Calculate offset about reconstructed contours, 4) Calculate intersection points between horizontal or vertical lines and offset contours for internal hatch, 5) Decide laser shutter on/off points. The algorithm developed and programmed by C language is verified as an efficient method after testing a number of STL files of mechanical parts.

• Journal of the Korea Concrete Institute
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• v.15 no.4
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• pp.625-633
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• 2003

For the construction of open-topped steel box girder bridges, prefabricated concrete slab could offer several advantages over cast-in-situ deck including good quality control, fast construction, and elimination of the formwork for concrete slab casting. However, precast decks without reinforcements at transverse joints between precast slabs should be designed to prevent the initiation of cracking at the joints, because the performance of the joint is especially crucial for the integrity of a structural system. Several prestressing methods are available to introduce proper compression at the joints, such as internal tendons, external tendons and support lowering after shear connection. In this paper, experimental results from a continuous composite bridge model with precast decks are presented. Internal tendons and external tendons were used to prevent cracking at the joints. Judging from the tests, precast decks in negative moment regions have the whole contribution to the flexural stiffness of composite section under service loads if appropriate prestressing is introduced. The validity of the calculation of a cracking load fur serviceability was presented by comparing an observed cracking load and the calculated value. Flexural behavior of the continuous composite beam with external prestressing before and after cracking was discussed by using the deflection and strain data.