• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 춘계학술대회 논문집
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• pp.67-70
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• 2008

This paper deals with the effect of radial parameters in cogging process such as reduction in height (Rh) and rotational angle ($\theta$) of a billet on a void closure for large forged products. Usually closing and consolidation of internal void defects in a ingot is a vital matter when utilized as large forged products, using a press with limited capacity and the sizes of the ingots becoming larger. Consequently, it is important to develop cogging process for improvement of internal soundness without a void defect and cost reduction by solid forging alone with limited press capacity. For experiments of cogging process, hydraulic press with a capacity of 800 ton was used together with a small manipulator which was made for rotation and overlapping of a billet. Size of a void was categorized into two types; $\emptyset$ 6.0 mm and $\emptyset$ 9.0 mm to investigate the change of closing and consolidation of void defects existed in the large ingot during the cogging process. Also open void and closed void in the ingot were tackled to show the differentiation of closing process of internal voids with respect to void sizes. In this paper systematic configuration for closing process of void defects were expressed based on this experiment results in the cogging process.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 춘계학술대회 논문집
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• pp.57-60
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• 2008

The studies for internal void closure have been conducted experimentally and numerically for open die forging. The FEM analysis is performed to investigate the deformation behavior of some internal voids in cast ingots during two upsetting stages. The calculated results of void closure behavior are compared with the measured results before and after upsetting. The shapes and sizes of each internal void are scanned by the X-ray scanner. From this result, the criteria for deformation amounts effect on the void closure can be investigated by the types of void. Closed voids could be compressed and eliminated after forging when the applied deformation amounts were larger than the critical effective strains. On the other hand, open voids could not be compressed and removed.

• Restorative Dentistry and Endodontics
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• 제45권1호
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• pp.5.1-5.8
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• 2020

Objectives: The obturation quality of MTA, Biodentine, Total Fill BC root canal sealer (RCS), and warm gutta-percha (WGP) in teeth with simulated internal root resorption (IRR) was evaluated by using micro-computed tomography. Materials and Methods: Standardized IRR cavities were created using 40 extracted maxillary central incisor teeth and randomly assigned into 4 groups (n = 10). IRR cavities were filled with MTA, Biodentine, Total Fill BC RCS (bulk-fill form) and WGP + Total Fill BC RCS. Percentage of voids between resorptive cavity walls and obturation material (external void), and inside the filling materials (internal voids) were measured. Results: Total Fill BC sealer in the bulk-fill form presented significantly highest values of external and internal void percentages (p < 0.05). Biodentine showed a significantly lowest external void percentage (p < 0.05). WGP + Total Fill BC RCS presented significantly lower values of internal void percentages than all groups (p < 0.05), except Biodentine (p > 0.05). Conclusion: None of the filling materials were created void-free obturation in resorption cavities. Biodentine may favor its application in teeth with IRR over Angelus MTA and bulkfill form of Total Fill BC.

• 대한기계학회논문집
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• 제16권10호
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• pp.1877-1889
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• 1992

본 연구에서는 업셋팅의 변형해석 및 온도해석(열전달 해석)을 비연계 방식으 로 동시에 해석하고 실제 공정에 가깝게 접근하는 축대칭 열점소성 유한요소 프로그램 을 이용하여, 시뮬레이션에 의해 공정을 해석하여 불량감소 및 원가절감을 위해 단조 공정을 개선하는 것이다. 업셋팅공정의 연구에 있어서는 대형강괴의 주 불량요인인 기공의 소멸을 위한 공정방안을 연구하는데 있다.

• Nutrition Research and Practice
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• 제14권1호
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• pp.25-31
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• 2020

BACKGROUND/OBJECTIVES: To date, sodium intake has been evaluated based on spot urine instead of 24-hour (hr) urine collection. Nevertheless, the optimal method for assessing daily sodium intake remains unclear. SUBJECTS/METHODS: Fifteen male (age 32.7 ± 6.5 years) participants were offered 3 meals with a total of 9-10 g salt over 24 hours, and 24-hr urine was collected from the second-void urine of the first day to the first-void urine of the second day. Twenty-four-hr urinary sodium (24UNa) was estimated using Tanaka's equation and the Korean formula, and spot urine Na, potassium (K), chloride (Cl), urea nitrogen (UN), creatinine (Cr), specific gravity (SG) and osmolality (Osm) were measured. The ratios of urinary Na to other parameters were calculated, and correlations with total measured 24UNa were identified. RESULTS: Average 24-hr urine volume was 1,403 ± 475 mL, and measured 24UNa was 143.9 ± 42.1 mEq (range, 87.1-239.4 mEq). Measured 24UNa was significantly correlated with urinary Na/UN (r = 0.560, P < 0.01), urinary Na/Osm (r = 0.510, P < 0.01), urinary Na/Cr (r = 0.392, P < 0.01), urinary Na/K (r = 0.290, P < 0.01), 24UNa estimated using Tanaka's equation (r = 0.452, P < 0.01) and the Korean formula (r = 0.414, P < 0.01), age (r = 0.548, P < 0.01), weight (r = 0.497, P < 0.01), and height (r = 0.393, P < 0.01) in all spot urine samples. Estimated 24UNa based on the second-void spot urine of the first day tended to be more closely correlated with measured 24UNa than were estimates from the other spot urine samples. The significant parameters correlated with the second-void urine of the first day were urinary Na/K (r = 0.647, P < 0.01), urinary Na/Cr (r = 0.558, P < 0.05), and estimated 24UNa using Tanaka's equation (r = 0.616, P < 0.05) and the Korean formula (r = 0.588, P < 0.05). CONCLUSIONS: Second-void urine is more reliable than first-void urine for estimating 24UNa. Urinary Na/K in the second-void urine on the first day is significantly correlated with 24UNa. Further studies are needed to establish the most reliable index and the optimal time of urine sampling for predicting 24UNa.

• Journal of the Korean Wood Science and Technology
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• 제36권6호
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• pp.13-22
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• 2008

보드의 기계적 성질에 영향을 미치는 공극에 대하여 공극을 두가지로 분류하고 밀도에 따른 오에스비의 내부 공극구조의 특성에 대하여 살펴보고자 하였다. 스트랜드보드의 내부공극을 X-ray 단층촬영기로 측정하고 이미지분석 소프트웨어를 사용하여 밀도에 따른 공극의 분포와 공극의 함유량을 조사하였다. 측정 전에 보드의 밀도를 밀도측정기와 전건법으로 측정하였으며 이 두 방법에 의해 측정된 결과는 아주 높은 상관관계를 보여주었다. X-ray를 서로 다른 배율로 조사하여 획득한 이미지를 바탕으로 분석한 결과, 저해상도에서는 스트랜드간의 공극(macro-void)의 측정이 가능하나 스트랜드내의 미세공극(micro-void)은 이미지획득이 불가능하였다. 중해상도에서는 두가지 형태 모두의 이미지 획득이 가능하였고, 고해상도에서는 대부분의 미세공극 이미지의 획득이 가능하였다. 저배율을 채택하여 스트랜드간의 공극을 측정하고 스트랜드내의 미세공극은 관련식을 이용하여 추정하였다. 이를 통해 보드내부에 존재하는 스트랜드간의 공극분포를 파악할 수 있었으며 그 공극의 함유비율을 정확하게 산정할 수 있었다.

• 한국안전학회지
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• 제31권4호
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• pp.75-81
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• 2016

This study presents the effect of urea and sulfur admixture on compressive strength, chloride diffusion coefficient, and internal void distribution of concrete. Compressive strength of concretes with urea admixture by 5% increased by 5% relative to Control. However, that of concretes with urea admixture over 10% decreased. Chloride diffusion coefficient of concrete with urea and sulfur admixture decreased by 40% relative to Control. Additionally, the volume of internal void of concrete with urea and sulfur admixture decreased by 20% relative to Control. Therefore, it can be mentioned from test results that the use of adequate urea and sulfur admixture improves the mechanical properties and durability of concrete.

• Progress in Superconductivity
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• 제10권2호
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• pp.108-115
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• 2009

As a participant taking part in the ITER TF conductor R&D program, we developed two toroidal field conductors with variations of conduit thickness resulting in the different void fraction of the conductors. The estimated void fractions of the conductors are 31% and 33%. In this paper we present the details of the TF conductor development and performance test results of them carried out by the measurement of current sharing temperature under cyclic loading. Regarding the conductor development, the internal-Sn-processed $Nb_3Sn$ strand characteristics, strand cabling, twist pitch and characteristics of the conduit materials are presented. For the understanding of the conductor design and performance, the conductor test results are presented and the effect of the conductor design parameters such as void fraction and twist pitch is discussed based on the results.

• 소성∙가공
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• 제5권1호
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• pp.18-26
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• 1996

In order to investigate the effect of pre-cooling of ingot on void closure in hot plate forging the internal strain and stress distributions are examined quantitatively by using ABAQUS. Simula-tions are carried out on a large slab ingot having the same temperature and the temperature gradient induced by air-cooling. It is shown that pre-cooling produces little effect on the strain behavior but remarkable effect on the hydrostatic stress at the central zone of ingot. The main factors for crushing micro-voids are the effective strain and the time integral of hydrostatic stress in the region surrounding the voids. Based on regression analysis it was found that the distortion of void can be expressed as a polynomial function of the two factors.

• 한국수소및신에너지학회논문집
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• 제16권4호
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• pp.324-333
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• 2005

The kinetics of external hydrogen embrittlememt is considered. The equation of the crack growth rate (CGR) is derived from modification of the model developed by Wilkinson and Vitek. After calculation of hydrogen pressure build-up in the void, the effect of the internal hydrogen pressure on the void growth is added. The CGR is expressed by two terms. One is the term dependent on the critical stress, which is exactly same as Wilkinson and Vitek. The other is term dependent on the pressure of the hydrogen in void.