유압벌지실험을 이용한 순 티탄늄 판재의 소성유동곡선 평가(제2보)

김영석(Kim, Young-Suk),김진재(Kim, Jin-Jae) 한국산학기술학회 2016 한국산학기술학회논문지 Vol.17 No.4

본논문에서는대형 선박의 판형열교환기등에 널리 이용되고있는 순 티타늄판재의소성변형을 유한요소해석하기 위한 기초 데이터로서 순 티타늄 판재의 유동곡선을 평가하였다. 순 티타늄 판재의 프레스 가공 시에 판재에는 국부적으로 큰 소성변형이 발생하고 있다. 그러나 기존의 단축 인장실험에서 얻을 수 있는 소성변형률이 낮아서 티타늄 판재의 가공공정 설계를 위한 유한요소해석의 정밀도를 떨어뜨리는 경우가 있다. 본 연구에서는 큰 소성변형률 까지 안정적으로 성형이 가능한 유압벌지실험을 수행하여 재료의 소성변형에서 가공경화특성을 나타내는 유동곡선으로써 진응력-진변형률 선도를 구하였고 그 결과를 인장실험 결과와 비교하였다. 순 티타늄 판재의 유압벌지실험에서 재료의 변형률은 3D 디지털 영상 상관법을 이용한 ARAMIS 시스템으로 실시간 측정된다. 이 유압벌지실험으로부터는 소성 변형률이 0.65 이상 까지도 안정적으로 재료의 소성유동곡선을 얻을 수 있었으며 그 결과는 Kim-Tuan 이 문헌 17[Y.S. Kim, J.H. In, Korean Acadmia-Ind. Coop. Soc.,(be in print), 2016] 의 연구에서 제안한 가공경화식으로 잘 핏팅됨을 알 수 있었다. In this study, the plastic flow curve of commercially pure titanium sheet (CP Ti) actively used in the plate heat exchanger etc., was evaluated. The plastic flow curve known as hardening curve is a key factor needed in conducting finite element analyses (FEA) for the forming process of a sheet material. A hydraulic bulge test was performed on the CP Ti sheet and the strain in this test was measured using the DIC method and ARAMIS system. The measured true stress-true strain curve from the hydraulic bulge test (HBT) was compared with that from the tensile test. The measured true stress-true strain curve from the hydraulic bulge test showed stable plastic flow curve over the strain range of 0.7 which cannot be obtained in the case of the uniaxial tensile test. The measured true stress-true strain curve from the hydraulic bulge test can be fitted well by the hardening equation known as the Kim-Tuan model.

대황황련해독탕의 항고지혈증 작용

김영석,정은아,장종철,양형길,조기호,배형섭,이경섭,김동현,김남재,Kim, Young-Suk,Jung, Eun-Ah,Chang, Jong-Chul,Yang, Hyung-Kil,Cho, Gi-Ho,Bae, Hyung-Sup,Lee, Kyung-Sup,Kim, Dong-Hyun,Kim, Nam-Jae 한국생약학회 2001 생약학회지 Vol.32 No.2

Whangryunhaedok-Tang (WT) is formulated with Coptidis Rhizoma, Phellodendri Cortex, Scutellariae Radix and Gardeniae Fructus, and Daewhang-whangryunhaedok-Tang (DWT) is made by the combination of Rhei Rhizoma, a wellknown anticostipation drug in WT. Therefore, DWT has been evaluated for antihyperlipidemic effects on experimental hyperlipidemic rats and mice induced by corn oil and high cholesterol-diet. Oral administration of DWT significantly inhibited the increase of serum triglyceride and LDL-cholesterol levels, and the decrease of serum HDL-cholesterol levels in hyperlipidemic rats induced by corn oil. Also, oral administration of DWT significantly prevented the increase of serum total cholesterol, triglyceride and LDL-cholesterol, and liver total cholesterol and triglyceride in 1% cholesterol-diet fed mice. These results suggest that DWT is effective for the treatment of hyperlipidemia.

중고시장의 고객만족경영: 셀잇(Sell-it) 사례를 중심으로

김영석,전다영,오주선,김나연,전원길,최지은,Kim, Young Suk,Jeon, Da Young,Oh, Ju Seon,Kim, Na Yeon,Jeon, Won Gil,Cho, Jieun 서비스사이언스학회 2016 서비스연구 Vol.6 No.3

As competition continues to increase, it becomes even more important for companies to improve customer satisfaction to survive. Many companies have tried to improve customer satisfaction in their own ways. This case study focuses on the market for used products, and introduces the case of the start-up company, SELL-IT, a company that has made great efforts to solve the problems commonly facing their customers and has been rewarded by improved customer satisfaction. Focusing on improving communications between buyers and sellers, the root of many problems in any market, SELL-IT has introduced a number of new systems to solve the problems that plague the secondhand market. This case study provides marketers with practical implications to improve customer satisfaction in the secondhand market. 기업 간의 경쟁이 격화된 상황에서 고객 만족을 향상하는 것은 매우 중요하다. 많은 기업은 각자의 방식을 통해 고객 만족 경영을 실현하려 한다. 본 사례연구에서는 중고거래시장에 초점을 맞추어, 중고거래에서 고객들이 봉착하게 되는 문제점들을 해결하고 고객 만족을 향상하고자 한 셀잇의 고객 만족 경영을 살펴보고자 한다. 셀잇은 기존 중고거래시장의 고질적인 문제점으로 지적되었던 커뮤니케이션 문제나 시스템 문제를 해결하고자 하였으며, 이러한 문제점을 해결함으로써 고객 만족 경영을 실현하고자 하였다. 본 사례연구에서는 이러한 셀잇의 사례를 통해 중고거래시장의 고객 만족을 향상하기 위한 실질적 방안을 제공하고자 한다.

순 티탄늄 판재의 프레스 성형성 평가(제 1보)

김영석(Kim, Young-Suk),인정훈(In, Jeong-Hun) 한국산학기술학회 2016 한국산학기술학회논문지 Vol.17 No.3

본 논문에서는 판형 열교환기 등에 널리 이용되고 있는 순 티타늄 판재의 프레스 성형성을 평가하기 위해 인장실험을 수행하였고 인장실험결과를 가장 잘 피팅할 수 있는 가공경화 모델을 제안하였다. 또한 항복곡면의 도출을 위해 단축변형, 평면변형, 순수전단변형 등 다양한 변형모드 하에서의 인장실험을 실시하였다. 이 제안된 모델을 Hora의 수정된 최대하중조건식에 적용하여 프레스 성형성을 평가하기 위해서 널리 사용되고 있는 성형한계선을 예측하였고 그 결과를 장출성형실험에서 구한 성형한계선과 비교하였다. 도출한 항복곡면을 잘 묘사하기 위한 이방성 항복조건식과 본 연구에서 제안된 가공경화모델은 순 티타늄 판재의 프레스 성형성의 척도인 성형한계선을 잘 예측함을 알 수 있었다. Commercially pure titanium (CP Ti) has been actively used in plate heat exchangers due to its light weight, high specific strength, and excellent corrosion resistance. However, compared with automotive steels and aluminum alloys, there has not been much research on the plastic deformation characteristics and press formability of CP Ti sheet. In this study, the mechanical properties of CP Ti sheet are clarified in relation to press formability, including anisotropic properties and the stress-strain relation. The flow curve of the true stress-true strain relation is fitted well by the Kim-Tuan hardening equation rather than the Voce and Swift models. The forming limit curve (FLC) of CP Ti sheet was experimentally evaluated as a criterion for press formability by punch stretching tests. Analytical predictions were also made via Hora's modified maximum force criterion. The predicted FLC with the Kim-Tuan hardening model and an appropriate yield function shows good correlation with the experimental results of the punch stretching test.

Ti-6Al-4V 합금의 수소지체균열속도 온도의존성

김영석(Young Suk Kim),최승준(Seung Jun Choi),정용무(Yong Moo Cheong) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.11

A Ti-6Al-4V sheet with the α-Ti and the β phase was subjected to electrolytic charging of 1000 ppm H and to constant load tests at temperatures varying from 10 ℃ to 200 ℃. The delayed hydride cracking velocity (DHCV) was determined using compact tension specimens with the pre-fatigued crack growing along the rolling direction of the sheet. The DHCV of the Ti-6Al-4V alloy decreased with the test temperature increasing from 20 to 100 ℃ and also with the test temperature decreasing below the zero temperature. This fact is quite in contrast with the DHCV of Zr-2.5Nb alloys that increases with the increasing temperature from RT to 300 ℃ and decreases at temperatures above 300 ℃. Based on Kim’s DHC model, we have discussed the different temperature dependency of the DHCV for the Ti-6Al-4V alloys and the Zr-2.5Nb both of which have the microstructure of the α- and β-phases.

다결정체의 탄소성 대변형해석

김영석,김정석,Kim, Young-Suk,Kim, Jung-Suk 대한기계학회 1997 大韓機械學會論文集A Vol.21 No.8

Elastic-plastic finite element(FE) simulation was performed for polycrystalline solids subjected to plane strain tensile loading. Using Asaro's double slip crystal plasticity model, the polycrystalline solids were modeled by assigning different initial slip directions to each grain. From the FE calculations, the microscopic deformation characteristics of polycrystalline solids were analyzed. Moreover, the effect of grain size and grain boundaries on the deformation characteristics were clarified.

Temperature Dependence of Delayed Hydride Cracking Crack Velocity in Zr-2.5Nb Tubes

Young Suk Kim(김영석) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11

Delayed hydride crack tests were conducted on Zr-2.5Nb tubes with different distributions of the β-Zr at temperatures ranging from 125 to 300 ℃. Compact tension specimens charged to 27 to 100 ppm hydrogen were used to determine temperature dependences of their DHC velocity (DHCV) and striation spacing. The Zr-2.5Nb tube with a higher yield strength and a seimi-continuous β-Zr has a higher DHCV and a smaller striation spacing than that with a fully discontinuous β-Zr and a lower yield strength. It is found that the activation energy for the DHCV is the sum of the activation energy for hydrogen diffusion and the striation spacing representing the hydrogen concentration gradient at the crack tip. Quantitative contribution of hydrogen diffusion nad the hydrogen concentration gradient to the DHCV is discussed. This study provides supportive evidence to the feasibility of Kim’s DHC model.

O, O'-Diethyl DL-1-Aminobenzylphosphonate와 그의 유도체들을 포함한 p-Acetamidobenzenesulfonamide의 합성

김영석,홍석인,김용준,Young Suk Kim,Suk In Hong,Yong Joon Kim 대한화학회 1983 대한화학회지 Vol.27 No.4

새로운 O, O'-diethyl-1-aminobenzylphosphonate와 그의 유도체들을 포함한 다음의 6가지의 p-acetamidobenzenesulfonamide를 합성하였다. O, O'-diethyl N-(p-acetamidobenzenesulfonyl) aminobenzylphosphonate, N-(p-acetamidobenzenesulfonyl) aminobenzylphosphonic acid, O,O'-diethyl N-[N-(p-acetamidobenzenesulfonyl) glycyl] aminobenzylphosphonate, O,O'-diethyl N-[N-(p-acetamidobenzenesulfonyl)-DL-alanyl] aminobenzylphosphonate, O,O'-diethyl N-[N-(p-acetamidobenzenesulfonyl)-L-leucyl] aminobenzylphosphonate, O,O'-diethyl N-[N-(p-acetamidobenzenesulfonyl)-L-phenylalanyl]aminobenzylphosphonate. 모든 화합물은 흰색 결정으로 얻었으며 적외선 분광법과 원소분석으로 확인되었다. Six new compounds of p-acetamidobenzenesulfonamides which contain O, O'-diethyl-1-aminobenzylphosphonate and their derivatives were prepared: O, O'-diethyl N-(p-acetamidobenzenesulfonyl) aminobenzylphosphonate, N-(p-acetamidobenzenesulfonyl) aminobenzylphosphonic acid, O,O'-diethyl N-[N-(p-acetamidobenzenesulfonyl) glycyl] aminobenzylphosphonate, O,O'-diethyl N-[N-(p-acetamidobenzenesulfonyl)-DL-alanyl] aminobenzylphosphonate, O,O'-diethyl N-[N-(p-acetamidobenzenesulfonyl)-L-leucyl] aminobenzylphosphonate, and O,O'-diethyl N-[N-(p-acetamidobenzenesulfonyl)-L-phenylalanyl]aminobenzylphosphonate. All the compounds were obtained as white crystals and characterized by means of elemental analysis and infrared spectroscopy.

엠보싱 알루미늄 판재의 기계적특성과 스프링백 평가 (제1보)

김영석(Kim, Young-Suk),조준행(Cho, Jun-Haeng),Van-Cuong Do,신동우(Do, Van-Cuong) 한국산학기술학회 2015 한국산학기술학회논문지 Vol.16 No.2

엠보싱된 알루미늄 판재는 표면적이 증가하여 방열효과가 뛰어나고 가공경화에 의해 굽힘강성이 증가하여 자동차 열차단기에 널리 사용된다. 하지만 판재의 특성상 주름발생률이 높아 프레스 성형에 많은 제약이 따른다. 본 연구에서는 3차원 구조 알루미늄 판재의 프레스 성형성 평가를 위한 기초연구로 3차원 구조 엠보싱 콘 형상 판재의 기계적특성을 평가 하고 굽힘실험을 통해 프레스 가공 후 발생하는 스프링백을 정량적으로 평가하였다. 엠보싱 판재는 패턴의 방향에 따라 인장특성이 상이하다. 특히 평행 엠보싱 시편의 경우 항복응력이 감소하며 대각 엠보싱 시편의 경우 항복응력이 증가하게 되고 영률의 감소가 크게 나타난다. 그 결과 굽힘 성형가공 후에 스프링 백에 영향을 미친다. Embossed aluminum sheets were been used in heat insulation purpose for automative exhaust parts because of increasing their surface areas and stiffness reinforcement. However, there are many restrictions because of high rate of wrinkle occurrence on press working. We have performed the tensile and bending tests for embossed sheets to clarity its mechanical properties and springback characteristics. Embossed aluminum sheets showed a different flow stress after plastic yielding due to flattening the embossed cone shape. Above all, yield stress of parallel embossed specimen decreases while its diagonal one increases and the decrease of young’s modulus in the embossed sheets contributes to the increase of springback amount.

우황청심원이 정상인의 뇌혈류 및 혈압에 미치는 영향

김영석,Kim, Young-Suk 대한한방내과학회 1999 大韓韓方內科學會誌 Vol.20 No.1

Uwhangchungsimwon(UC) has been used in the treatment of a wide variety of conditions including stroke, hypertension, arteriosclerosis, autonomic imbalance, mental instablity, etc in Korean traditional hospitals, In particular it is often initialy chosen for emergency care of acute stroke. The aim of this study was to evaluate the effect of UC on cerebral hemodynamics. Using transcranial Doppler ultrasound, we studied changes of mean flow velocity and pulsatility index(PI) of middle cerebral arteries (MCAs) from 11 health young volunteers who were administrated with 1 pill UC and 11 health controls who were not. We obtained hypercapnia with breath-holding and evaluated cerebrovascular reactivity with breath-holding index(BHI). Systolic blood pressure, diastolic blood pressure, and heart rate were measured using ambulatory blood pressure monitoring(ABPM). In UC administration group, the evaluation was performed during basal condition. and repeated at 20, 40, and 60 min after administration. In controls, the evaluation was performed at corresponding time intervals. Mean flow velocity in middle cerebral artery, systolic blood pressure, diastolic blood pressure, and heart rate did not change during the observation period and were not different between these two groups. However, administration of UC was associated with decreases in PI by $3.6{\sim}12.4%$ in BHI by $17.9{\sim}24.8%$ compared with pre-administration period. Decreases in PI and BHI with UC were significantly different compared with control group (p<0.05). These results indicate that UC decreases PI and BHI in cerebral artery, which is due to a dilation of cerebral resistance vessels.