• 대한기계학회논문집
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• 제12권6호
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• pp.1350-1357
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• 1988

A computer software was developed for predictions of fatigue crack initiation life of notched members under variable loadings. The software was constructed based on a new fatigue life prediction method utilizing modified .epsilon.-N curves, which can account for the stress interaction effect. The effect of mean plastic strain on low-cycle fatigue life was also incorporated in the software. The software can be utilized for the first step approximation when fundamental data of material fatigue properties are not available.

• 대한기계학회논문집A
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• 제30권11호
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• pp.1425-1432
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• 2006

Coating layers on a coated sheet steel frequently affect distributions of strain rate of sheets and deteriorate the frictional characteristics between sheets and tools in sheet metal forming. Thus, it is important to identify the deformation behavior of these coatings to ensure the success of the sheet forming operation. In this study, the technique using nano-indentation test, FE-simulation and Artificial Neural Network(ANN) were proposed to determine the power law stress-strain behavior of coating layer and the power law behavior of extracted coating layers was examined using FE-simulation of drawing and nano-indentation process. Also, deep drawing test was performed to estimate the formability and frictional characteristic of coated sheet, which was calculated using the linear relationship between drawing force and blank holding force obtained from the deep drawing test. FE-simulations of the drawing process were respectively carried out for single-behavior FE-model having one stress-strain behavior and for layer-behavior FE-model which consist of coating and substrate separately. The results of simulations showed that layer-behavior model can predict drawing forces with more accuracy in comparison with single-behavior model. Also, mean friction coefficients used in FE-simulation signify the value that can occur maximum drawing force in a drawing test.

• 한국지반공학회논문집
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• 제15권1호
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• pp.175-183
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• 1999

최근 우리나라도 내진설계의 필요성에 따라 지진시 등의 고변형률로부터 정밀기계기초에 미치는 미소변형률 진동까지 기초지반의 동적거동에 관한 연구가 점증하고 있는 실정이다. 한편, 화강풍화토는 국내에 가장 널리 분포되어 있는 대표적인 흙으로써 지반진동문제 해결에 필요한 지반계수 등의 동적거동 파악이 시급한 형편이나 이에 관한 연구는 극히 한정되어 있다. 본 연구는 수원지방의 화강풍화토에 대하여 간극비, 포화도가 다른 공시체를 제작하여 구속압력 및 반복응력비를 변화시켜 공진주시험과 반복삼축시험을 실시하여 불포화 화강풍화토의 동적거동을 고찰하였고 지반보강을 위하여 흔히 사용되는 흙-시멘트 혼합토에 대하여도 시멘트 혼합비와 간극비를 달리한 공시체에 대하여 같은 조건하에 동적거동을 구명하기 위한 두가지 같은 실험을 수행하였다. 연구결과 불포화 화강풍화토의 전단탄성계수는 표면장력에 지배되며 최적포화도는 간극비에 따라 공진주 시험인 경우 약 17%~l8%, 반복삼축시험인 경우 약 10%~l5% 로 나타났다. 또한, 수원지역의 화강풍화토에 대한 한계 변형률 범위와 평균전단탄성계수도 추정할 수 있었다. 한편, 일련의 공진주시험과 반복삼축시험의 결과를 토대로 하여 화강풍화토의 시멘트 혼합량에 따른 최대전단탄성계수 추정식을 비교적 조밀한 경우와 비교적 느슨한 경우로 나누어 제안하였다.

• The Korean Journal of Physiology and Pharmacology
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• 제20권6호
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• pp.621-628
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• 2016

Hypertension can be caused by various factors while the predominant causes include increase in body fluid volume and resistance in the circulatory system that elevate the blood pressure. Consumption of probiotics has been proven to attenuate hypertension; however, the effect is much strain-dependent. In this study, a newly isolated Lactobacillus casei (Lb. casei ) strain C1 was investigated for its antihypertensive properties in spontaneously hypertensive rats (SHR). Lactic acid bacteria (LAB) suspension of 11 log colony-forming unit (CFU) was given to SHR (SHR+LAB, n=8), and phosphate buffer saline (PBS) was given as a control in SHR (SHR, n=8) and in Wistar rats as sham (WIS, n=8). The treatment was given via oral gavage for 8 weeks. The results showed that the weekly systolic blood pressure (SBP), mean arterial pressure (MAP), diastolic blood pressure (DBP) and aortic reactivity function were remarkably improved after 8 weeks of bacterial administration in SHR+LAB. These effects were mostly attributed by restoration of wall tension and tensile stress following the bacterial treatment. Although not statistically significant, the level of malondialdehye (MDA) in SHR+LAB serum was found declining. Increased levels of glutathione (GSH) and nitric oxide (NO) in SHR+LAB serum suggested that the bacterium exerted vascular protection through antioxidative functions and relatively high NO level that induced vasodilation. Collectively, Lb. casei strain C1 is a promising alternative for hypertension improvement.

• 식물병연구
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• 제13권3호
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• pp.137-144
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• 2007

거봉 포도나무에 혹병을 일으키는 A. vitis 균주간의 DNA 다양성 평가를 하기 위하여 12종류의 URP primer 적용 성을 조사한 결과 URP1F, URP2F, URP2R, URP4R, URP17R primer가 균주 간 DNA 다형성검정에 유용하였다. 국내외에서 분리한 59 A. vitis 균주를 URP-PCR 증폭하였던 바 균주간의 매우 다양한 PCR 다형성 밴드를 형성 하였으며 12 strain type으로 나눌 수 있었으며 거봉포도로부터 분리된 A. vitis 균주는 4 strain type의 비교적 단순한 유전적 다양성으로 나타났으나, 거봉이외의 다른 포도 품종이나 국외에서 도입된 A. vitis 균주는 8 strain type의 많은 유전적 다양성을 보여 거봉품종 유래 국내 균주와는 PCR 다형성 type에 있어 차이점을 보였다. URP-PCR 다형성 밴드를 집괴 분석하여 UPGMA dendrogram을 작성한 결과 7개의 대 Group으로 분류할 수 있었으며, 그룹 간에는 $62{\sim}100$%까지 다양한 유전적 유사성이 나타났다.

• 대한기계학회논문집
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• 제17권6호
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• pp.1321-1329
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• 1993

본 연구에서는 이들보다 매우 간단한 IS법, 즉 초기 변형률법(ISM: initial strain method)에 의한 크리프 수명예측식을 고안하여, 현재 화력발전용 고압 로터강 에 사용되고 있는 1%Cr-Mo-V강과 발전소 효율향상을 위해 최근 국내최초로 개발된 12% Cr강에 대하여 도출하였고, 이 도출식이 앞에서 언급한 여러 파라메트에 의한 결과와 비교 평가하여 장시간 강도 및 수명예측식으로 사용될 수 있음을 입증하였다.

• 대한기계학회논문집A
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• 제25권10호
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• pp.1528-1534
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• 2001

In order to improve Leak-Be(ore-Break methodology, more precisely the crack growth evaluation, a round robin analysis was proposed by the CEA Saclay. The aim of this analysis was to evaluate the crack initiation life, penetration life and shape of through wall crack under cyclic bending loads. The proposed round robin analysis is composed of three main topic; fatigue crack initiation, crack propagation and crack penetration. This paper deals with the first topic, crack initiation in a notched pipe under four point bending. Both elastic-plastic finite element analysis and Neuber's rule were used to estimate the crack initiation life and the finite element models were verified by mesh-refinement, stress distribution and global deflection. In elastic-plastic finite element analysis, crack initiation life was determined by strain amplitude at the notch tip and strain-life curve of the material. In the analytical method, Neuber's rule with the consideration of load history and mean stress effect, was used for the life estimation. The effect of notch tip radius, strain range, cyclic hardening rule were examined in this study. When these results were compared with the experimental ones, the global deformation was a good agreement but the crack initiation cycle was higher than the experimental result.

• 대한기계학회논문집A
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• 제36권10호
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• pp.1163-1169
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• 2012

초탄성 재료인 고무는 타이어의 주 원료인데, 주행 중 다양한 형태의 하중을 받는다. 그와 같은 하중에 의하여 타이어에 변형률에너지가 축적되어 파손에 이르게 된다. 일반적으로 초탄성재료인 고무는 금속과 다른 응력연화 특성을 갖고 있기 때문에 금속의 시험법을 적용할 수 없다. 따라서 본 연구에서는 조성비가 다른 2 종의 타이어용 고무에 대한 피로특성을 평가하기 위하여, ASTM D4482 규격에서 요구하는 변형률 범위를 확장하여 인장 및 피로시험을 진행하였으며, 실험 결과를 이용하여 피로수명식을 제안하였다.

• 대한치과보철학회지
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• 제41권2호
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• pp.243-257
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• 2003

The purpose of this study was to search the influences of the increase of the contents of sodium alginate in the experimental alginates on the some mechanical properties. 3 commercial alginates were selected for the purpose of comparison of the results of experiments. 7 experimental alginates were manufactured with the rise of contents of sodium alginate from 8.8% to 18.3% with the decrease of contents of diatomaceous earth and with the constant contents of calcium sulfate 12.5%. sodium phosphate 2.2%, zinc fluoride 2.0%. Splitable metal mold with 12.5mm diameter and 20.0mm height was filled with mixed alginate to prepare the cylinder shaped specimens. Strain in compression, elastic recovery, compressive strength were tested using the ISO specification number 1563, alginate impression material. Experimental groups were 7, and 10 specimens were used for each test items and each groups. Following results were obtained ; 1. Strain in compression was decreased with the increase of sodium alginate contents (p=0.0077, r2 = 0.6302). 2. Elastic recovery was decreased with the increase of sodium alginate contents but was not significant(p=0.0639, r2=0.7449). 3. Compressive strength was increased with the increase of sodium alginate contents (p<0.0001, r2 = 0.9617). These results mean that the increase of sodium alginate contents make alginate harder but may result the increased permanent deformation.

• 대한수의학회지
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• 제44권4호
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• pp.539-549
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• 2004

Mean death time of inoculated embryonated egg is one of the methods to determine the virulence of the Newcastle disease viruses (NDV). Evaluation of tissue tropism of NDV in the host has been proposed as an another way to determine the pathogenicity of NDV based on the principal site of viral replication. To evaluate the tissue tropism among NDV, an immunohistochemistry(IHC) technique using monoclonal antibody was applied in one-day-old SPF chickens inoculated with different ND vaccine strains such as Ulster 2C, VG/GA and B1 viruses by eye drop instillation. The tissues used for this comparison were trachea, intestine, Harderian gland and cecal tonsil, which were collected at 0.5, 1, 2, 3, 5, 8, 10, 14 days post inoculation. Among test groups, chickens inoculated with B1 viurs, which is known to replicate in the respiratory system, have IHC positive staining mainly in the trachea and those inoculated with Ulster 2C have IHC positive staining mainly in the intestine. However, chickens inoculated with VG/GA strain have IHC positive staining in both the trachea and intestine. Therefore, a differences in tissue tropism among ND vaccine strains has been proved by the IHC technique. Based on this results, the IHC staining technique could be used to classify the NDV or to study the pathogenesis of NDV in chickens.