기계적 분쇄화법으로 제조된 (Ti52Al48)100-xBx(X=0,0.5,2,5) 합금의 미세조직 및 기계적 성질

표성규,김낙준,정현호,황승준 대한금속재료학회(대한금속학회) 1998 대한금속·재료학회지 Vol.36 No.12

The present study is concerned with γ-(Ti_(52)Al_(48))_(100-x)B_x(x=0, 0.5, 2, 5) alloys produced by mechanical milling/vacuum hot pressing using melt-extracted powders. Microstructure of as-pressed alloys exhibit dual phase equiaxed microstructure of α₂ and γ with a mean grain size of 200 ㎚. Besides α₂ and γ phase, binary and 0.5%B alloys contains Ti₂AlN and Al₂O₃ phases located along the grain boundaries and show appreciable coarsening in grain and dispersoid sizes during annealing treatment at 1300℃ for 5 h. On the other hand, 2%B and 5%B alloys contains fine boride particles within the γ grains and show minimal coarsening during annealing. Room temperature compression tests of as-pressed alloys reveal low ductility, but very high yield strength >2100 ㎫. After annealing treatment, mechanically milled alloys show much higher yield strength than conventional PM and IM processed alloys, with equivalent ductility to IM processed alloys. 5%B alloy with smaller grain size shows higher yield strength than binary alloy at room temperature. When test temperature is increased to 850℃ 5%B alloy shows much lower strength than binary alloy, indicating the deformation of fine 5%B alloy is dominated by the grain boundary sliding mechanism.

만성신부전증에서 혈청 CEA치에 관한 연구

이정상,신영태,정순일,고창순,김성권,표희정,권인순 대한핵의학회 1980 핵의학 분자영상 Vol.14 No.2

저자들은 1979년 3월부터 1980년 10월까지 서울대학교병원내과에 입원하여 만성신부전증으로 진단받고 혈액투석요법을 받지 않은 환자 15예, 혈액투석요법을 시행중인 환자 39예 및 신장이식술을 받고 신장능이 호전된 환자 23예에서 혈청 CEA치를 방사면역측정법으로 측정하여 정상대조군과 비교하여 다음과 같은 결과를 얻었다. 1) 정상 성인 65명의 혈청 CEA치의 범위는 1.0∼4.3 ng/ml이었으며 평균은 1.6±0.66 ng이었다. 2) 혈액투석요법을 시행치 않은 만성신부전증 환자 15예의 혈청 CEA치는 0.3∼8.3 ng/ml이었고 평균은 3.6±2.10 ng/ml로써 정상대조군에 비하여 유의하게 증가되어 있었다(p$lt;0.001). 3) 혈액투석요법으로 치료중인 만성신부전증 환자 39예의 혈청 CEA치는 0.7∼6.7 ng/ml로 평균이 3.0±1.52 ng/ml이며, 정상대조군에 비하여 유의하게 상승되어 있으나(p$lt;0.001), 혈액투석을 받지 않은 환자군과는 유의한 차이가 없었다. 4) 신이식 환자 23예의 혈청 CEA치의 분포는 1.8∼10.8 ng/ml이고 평균은 3.8±1.96 ng/ml로 역시 정상대조군에 비하여 유의하게 증가되어 있으나(p$lt;0.001), 만성신부전증 환자군과는 유의한 차이가 없었다. 5) 이상의 혈청 CEA치가 정상범위 이상으로 상승된 49명��환자중 이학적 소견이나 검사소견상 악성종양은 발견되지 않았다. The serum CEA levels were measured by radioimmunoassay technique in 15 patients with chronic renal failure, who were not treated with hemodialysis, in 39 patients under hemodialysis and in 23 patients who received renal transplantation. The results were compared with those in 65 normal adults and the following results were obtained. 1) Serum CEA concentrations in 65 normal adults were in the range of 1.0 to 4.3 ng/ml with a mean value of 1.6±0.66 ng/ml. 2) Serum CEA concentrations in 15 chronic renal failure patients who were not treated with hemodialysis, were in the range of 0.3 to 8.3 ng/ml with a mean value of 3.6±2.10 ng/m1 which was significantly higher than those of normal controls(P$lt;0.001). 3) Serum CEA concentrations in 39 chronic renal failure patients under hemodialysis were also much higher than normal controls(p$lt;0.001), but not significantly different from those of the patients who were not under hemodialysis(P$gt;0.05). 4) In 23 patients who received renal transplantation, serum CEA levels were snificantly higher than normal controls(P$lt;0.001), but not significantly different from those of chronic renal failure patients.

당뇨병에서의 혈장 Renin 활성에 관한 연구

이정상,이문호,김성권,최강원,표희정,박정식 대한핵의학회 1979 핵의학 분자영상 Vol.13 No.1

당뇨병에서의 고혈압 및 신합병증에 따른 Renin Angiotensin-Aldosterone계의 동태를 밝히기 위하여 40예의 당뇨병 환자에서 기저 및 furosemide 정주 2시간 후의 PRA를 측정하였다. 1) 40예의 당뇨병 환자는 신합병증과 고혈압의 유무에 따라 4군으로 분류하였으며, 임상적인 합병증이 없는 Ⅰ군에는 15명, 신합병증이 있는 Ⅱ군에는 7명, 신합병증과 고혈압이 같이 있는 Ⅲ군에는 8명, 고혈압만 있는 Ⅳ군에는 10명의 환자가 속하였다. 2) 각 군의 24시간 요중 Na배설량의 평균치 사이에는 유의한 차이가 없었다. 3) 기저 PRA치는 Ⅰ군이 1.53±1.09ng/ml/hr(Mean±S.D), Ⅱ군이 0.63±0.59ng/ml/hr, Ⅲ군이 0.79±0.62ng/ml/hr, Ⅳ군이 1.11±0.80ng/ml/hr로서 Ⅱ군과 Ⅲ군은 Ⅰ군에 비하여 유의하게 저하되어 있으나(P$lt;0.05), 다른 군들 간에는 유의한 차를 볼 수 없었다. 4) furosemide 정주 2시간 후의 PRA치는 Ⅰ군이 2.72±1.96ng/ml/hr, Ⅱ군이 0.92±0.78ng/ml/hr, Ⅲ군은 1.03±0.76ng/ml/hr, Ⅳ군은 1.73±1.39ng/ml/hr로써 Ⅰ군과 Ⅱ군사이에서만 유의한 차이를 보이고(P$lt;0.05), 다른 당뇨병 환자군 사이에서는 유의한 차를 볼 수 없었다. 5) furosemide 정주에 의한 Renin 분필 자극시험에 대한 반응도 Ⅱ군과 Ⅲ군에서는 둔화되어 있는 양상을 보이나, 시험대상도 적고하여 통계적 유의성에는 미치지 못하였다. 이상의 성적에서 신합병증이 있는 당뇨병에서는 혈장 Renin활성이 저하되며 furosemide 정주에 의한 Renin 분필자극시험에 대한 반응도 둔화됨을 알 수 있었다. 또한 당뇨병성 신합병증에 의한 고혈압에서도 혈장 Renin활성은 저하되는 경향을 보여서 이 경우의 고혈압은 Renin이외의 다른 요인이 작용할 것으로 보인다. To evaluate the renin-angiotensin-aldosterone system in diabetes mellitus, basal plasma renin activity(PRA) and its response to intravenous furosemide were determined in 40 diabetic subjects. The diabetics were divided into 4 groups according to the pressence of nephropathy and/or hypertension. Uncomplicated diabetics(Group I) were taken as control group and the results of the other groups were compared to this group. In diabetics viith nephropathy alone(Group Ⅱ), and with nephropathy and hypertension (Group Ⅲ), basal PRA values were 0.63±0.59ng/ml/hr., and 0.79±0.62ng/ml/hr., respectively, both significantly lower than control group. (1.53±1.09ng/ml/hr.). (P$lt;0.05) In both of the above groups, the responses to intravenous furosemide tended to be blunted. On the other hand, in diabetics, with hypertension only (Group Ⅳ), the basal and stimulated PRA were not significantly different from control. Above results suggests that nephropathy may be one of the factors which suppress renin activity in diabetes me.

원전 배관의 LBB 개념 적용을 위한 간략 설계기법 개발

이철형,김영진,표창률,석창성,허남수 한국산업안전학회 1999 한국안전학회지 Vol.14 No.2

If the Leak-Before-Break (LBB) concept is applicable to the nuclear piping design, it is not necessary to consider the dynamic effect due to pipe rupture. Therefore, the construction cost can be significantly reduced by eliminating unnecessary pipe whip restraints and jet impingement devices. The objective of this paper is to develop the Piping Evaluation Diagram (PED) for efficient application of LBB concept to piping system at an initial piping design stage. For this purpose, the 3-D finite element analyses were performed to evaluate the crack stability. And the stress-strain curve based on the pipe material tests were used to calculate the detectable leakage crack length. Finally, the present PED which was composed as a function of NOP load and allowable SSE load, was developed for an application of LBB concept to the safety injection and shutdown cooling line in Korean Next Generation Reactor (KNGR).

두께가 일정하지 않은 재료에서 경사진 균열의 성장거동에 관한 연구

조명래,표창률,박종구,고명훈 한국산업안전학회 1997 한국안전학회지 Vol.12 No.4

The effect of geometry factors on the combined mode stress intensity factor behaviors of a slant crack in a non-uniform thickness material was analysed by 2-dimensional theoretical analysis. The analysis is based on the Laurent's series expansions of complex potentials where the complex coefficients of the series are determined from the compatibility and the equilibrium conditions of the thickness interface. and the stress free conditions of the crack surface. In numerical calculations the perturbation technique is employed. The expressions for the crack tip stress intensity factor are given in the form of power series of dimensionless crack length λ, and the function of crack slant angle α and thickness ratio β . The results of numerical calculations for each problems are represented as the correction factors F(λ, α, β). The results clearly show the following characteristics : The correction factors of the combined mode stress intensity factors for a non-uniform thickness material can be defined in the form of F(λ, α, β). The stress intensity factor values for a given crack length are decreased with increase of thickness ratio β.

기계적 합금화법으로 제조된 (Ti52Al48)100-xBx 합금의 미세조직 형성과정

표성규,김낙준,정현호,김상혁,황승준 대한금속재료학회(대한금속학회) 1998 대한금속·재료학회지 Vol.36 No.11

The main objective of this study is to investigate the microstructural evolution during mechanical milling of prealloyed (Ti_(52)Al_(48))_(100-x)B_x powders and also to investigate the effects of B contents and heat treatment on the microstructure of mechanically milled TiAl alloys. Microstructure of binary Ti_(52)Al_(48) Powders consists of grains of hexagonal phase whose structure is very close to Ti₂Al. (Ti_(52)Al_(48))_(95)B_5 powders contain TiB₂ in addition to matrix grains of hexagonal phase. The grain sizes in the as-milled powders of both alloys are nanocrystalline. The mechanically alloyed powders were consolidated by vacuum hot pressing (VHP) at 1000℃ for 2 hours, resulting in a material which is fully dense. Microstructure of consolidated binary alloy consists of γ-TiAl phase with dispersions of Ti₂AlN and A1₂O₃ phases located along the grain boundaries. Binary alloy shows a significant coarsening in grain and dispersoid sizes. On the other hand, microstructure of B containing alloy consists of γ-TiAl grains with fine dispersions of TiB₂ within the grains and shows the minimal coarsening during annealing.

레이저 용접을 위한 박판재의 정밀 전단 메카니즘 개발 : 유한요소법을 이용한 정밀 전단 공정해석 Analysis of Precise Shearing Process using FEM

조명래,표창률,전병희 한국산업안전학회 1999 한국안전학회지 Vol.14 No.4

Recently, Tailor Welded Blank (TWB) is widely used in automotive industry since the trans formation characteristic of its material can be changed. However, clearance between welding surfaces becomes the important factor which affect the quality of the laser weld, causing difficulties in preparing the sheet. The objective of this paper is to systematically evaluate the effects of previously presented fracture criterion and shearing condition on precise mechanical shearing simulation result. For this purpose, a parametric study was performed to investigate the effect of finite element size and fracture criterion on simulation result. Also, in order to predict the optimum shearing condition, effect of shearing conditions such as clearance and punch radius on the shear plane shape was evaluated.

Micromechanics-based elastic-damage analysis of laminated composite structures

Pyo, S.H.,Lee, H.K. Pergamon Press ; Elsevier Science Ltd 2009 International journal of solids and structures Vol.46 No.17

Based on the micromechanics-based constitutive model, derived in our preceding work [Lee, H.K., Pyo, S.H., 2009. A 3D-damage model for fiber-reinforced brittle composites with microcracks and imperfect interfaces. Journal of Engineering Mechanics-ASCE, in press, doi:10.1061/(ASCE)EM.1943.7889.0000039.], incorporating a multi-level damage model and a continuum damage model, the overall elastic behavior and damage evolution of laminated composite structures are studied in detail. The constitutive model is implemented into the finite element program ABAQUS using a user-subroutine UMAT to solve boundary value problems of the composite structures. The validity of the implemented constitutive model is assured by comparing the predicted stress-strain curves with experimental data available in literature under uniaxial tension with various fiber orientations. The results show that the proposed micromechanics-based constitutive model accurately predict the overall elastic-damage behavior of laminated composite structures having different material compositions, thicknesses and boundary conditions.

Fabrication of high quality carbonaceous coating on Cu nanoparticle using poly(vinyl pyrrolidone) and its application for oxidation prevention

Pyo, Youngjun,Choi, Dahyun,Son, Yeon-Ho,Kang, Suhee,Yoon, Eric H.,Jung, Seung-Boo,Kim, Yongil,Lee, Caroline Sunyong IOP Publishing 2016 Japanese journal of applied physics Vol.55 No.5

<P>A novel method of carbonaceous coating on the surface of copper particles was developed through a chemical vapor deposition (CVD) process to prevent the oxidation of copper nanoparticles (CNPs). The types of poly(vinyl pyrrolidone) (PVP) used were K-12 (M-W 3,500) and K-30 (M-W 45,000). The amounts of PVP used ranged from 10 to 50 wt %. Additionally, processing temperatures of 900 and 875 degrees C were tested and compared. The optimum CVD process conditions for the carbonaceous coating were as follows: 875 degrees C processing temperature, 50wt% K12 PVP solution, and gas conditions of Ar : H-2 = 1 : 1. The resistivity change in the fabricated copper pattern was confirmed that the initial resistivity value of the ink with a mixing ratio of carbonaceous-coated CNPs to 1-octanethiol-coated CNPs of 4 : 6 (w/w) maintained its initial resistivity value of 2.93 x 10(-7) Omega.m % m for more than 210 days. (C) 2016 The Japan Society of Applied Physics</P>

Characteristic of (La_0.8Sr_0.2)_0.98MnO₃ coating on Crofer22APU used as metallic interconnects for solid oxide fuel cell

Pyo, S.S.,Lee, S.B.,Lim, T.H.,Song, R.H.,Shin, D.R.,Hyun, S.H.,Yoo, Y.S. Pergamon Press ; Elsevier Science Ltd 2011 INTERNATIONAL JOURNAL OF HYDROGEN ENERGY - Vol.36 No.2

This study reports the high temperature oxidation kinetics, area specific resistance (ASR), and interfacial microstructure of metallic interconnects coated by (La<SUB>0.8</SUB>Sr<SUB>0.2</SUB>)<SUB>0.98</SUB>MnO<SUB>3</SUB> (LSM) in air atmosphere at 800<SUP>o</SUP>C. An efficient LSM conductive layer was fabricated on metallic interconnects for solid oxide fuel cells (SOFCs) by using a wet spray coating method. The optimum conditions for slurries used in the wet spray coating were determined by the measurement of slurry viscosity and coated surface morphology. The surface roughnesses of the substrates were increased through sandblast treatment. The adhesive strength of the interface between the coated layer and the metal substrate increased with increased surface roughness of the metallic interconnects. The electrical conductivities of the coated substrates were measured by using a DC two-point and four-wire method under air atmosphere at 800<SUP>o</SUP>C. Of note, the Crofer22APU treated at 1100<SUP>o</SUP>C in N<SUB>2</SUB> with 10vol.% H<SUB>2</SUB> showed long-term stability and a lower ASR value than other samples(heat-treated at 800<SUP>o</SUP>C and 900<SUP>o</SUP>C). After an 8000-h oxidation experiment the coated Crofer22APU substrate, the ASR showed a low value of 23m@?cm<SUP>2</SUP>. The thickness of the coated conductive oxide layer was about 10-20μm. These results show that a coated oxide layer prevents the formation and the growth of scale (Cr<SUB>2</SUB>O<SUB>3</SUB> and (Mn, Cr, Fe)<SUB>3</SUB>O<SUB>4</SUB> layer) and enhances the long-term stability and electrical performance of metallic interconnects for SOFCs.