• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2010년도 춘계학술발표대회 초록집
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• pp.58-58
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• 2010

The purpose of this study is to evaluate the structural safety at the topside weldment of hull structure, which was welded after launching. For it, the variations of residual stress and distortion at the topside weldment with loading conditions such as hull girder hogging bending moment after launching and free initial loading state was evaluated by using FEA. And the maximum stress range at the weldment under design loads specified by classification society was evaluated by FEA. In this case, the residual stress and welding distortion at the topside weldment was assumed to be initial imperfection. In accordance with FEA results, regardless of initial loading condition, tensile residual stress was found. However, the residual stress and welding distortion at the topside weldment produced under hogging condition was less than those of topside weldment under free loading state. That is, the amount of residual stress at the topside weldment decreased with an increase in the amount of tension load caused by hogging condition. It was because the compressive thermal strain at the topside weldment produced during welding was reduced by tensile load. However, the maximum stress range at the topside weldment under maximum hull girder bending moment was almost similar regardless of initial loading condition. So, if the problem related to the soundness of weldment is not introduced by initial load, the effect of initial loading condition during welding on fatigue strength of topside weldment could be negligible.

• 동력기계공학회지
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• 제9권4호
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• pp.96-101
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• 2005

Magnesium alloys have been widely used for many structural components of automobiles and aircraft because of high specific strength and good cast ability in spite of hexagonal closed-packed crystal structure of pure magnesium. In this study, uniaxial tension tests at high temperature and creep tests are done in order to investigate the characteristics of high temperature and mechanisms for creep deformation of AZ31 Mg alloy. Yield stress and ultimate tensile stress decreased with increasing temperature, but elongation increased from results of uniaxial tension test at high temperature. The apparent activation energy Qc, the applied stress exponent n and rupture life have been determined during creep of AZ31 Mg alloy over the temperature range of 473K to 573K and stress range of 23.42 MPa to 93.59 MPa, respectively, in order to investigate the creep behavior. Constant load creep tests were carried out in the equipment including automatic temperature controller, whose data are sent to computer. At around the temperature of $473K{\sim}493K$ and under the stress level of $62.43{\sim}93.59%MPa$, and again at around the temperature of $553K{\sim}573K$ and under the stress level of $23.42{\sim}39.00MPa$, the creep behavior obeyed a simple power-law relating steady state creep rate to applied stress and the activation energy for the creep deformation was nearly equal, respectively, and a little low to that of the self diffusion of Mg alloy including aluminum. Also rupture surfaces at high temperature have had bigger dimples than those at lower temperature by SEM.

• Structural Engineering and Mechanics
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• 제53권2호
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• pp.311-324
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• 2015

The purpose of this study was to investigate experimentally the fatigue performance of reinforced concrete (RC) beams with hot-rolled ribbed fine-grained steel bars of yielding strength 500MPa (HRBF500). Three rectangular and three T-section RC beams with HRBF500 bars were constructed and tested under static and constant-amplitude cyclic loading. Prior to the application of repeated loading, all beams were initially cracked under static loading. The major test variables were the steel ratio, cross-sectional shape and stress range. The stress evolution of HRBF500 bars, the information about crack growth and the deflection developments of test beams were presented and analyzed. Rapid increases in deflections and tension steel stress occured in the early stages of fatigue loading, and were followed by a relatively stable period. Test results indicate that, the concrete beams reinforced with appropriate amount of HRBF500 bars can survive 2.5 million cycles of constant-amplitude cyclic loading with no apparent signs of damage, on condition that the initial extreme tensile stress in HRBF500 steel bars was controlled less than 150 MPa. It was also found that, the initial extreme tension steel stress, stress range, and steel ratio were the main factors that affected the fatigue properties of RC beams with HRBF500 bars, whose effects on fatigue properties were fully discussed in this paper, while the cross-sectional shape had no significant influence in fatigue properties. The results provide important guidance for the fatigue design of concrete beams reinforced with HRBF500 steel bars.

• Earthquakes and Structures
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• 제20권1호
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• pp.71-86
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• 2021

This paper focuses on the development and assessment of the expected damage for the rocking response of rigid anchored blocks, with irregular geometry and non-uniform mass distribution, considering the site conditions and the seismicity of Mexico City. The non-linear behavior of the restrainers is incorporated to evaluate the pure tension and tension-shear failure mechanisms. A probabilistic framework is performed covering a wide range of block sizes, slenderness ratios and eccentricities using physics-based ground motion simulation. In order to incorporate the uncertainties related to the propagation of far-field earthquakes with a significant contribution to the seismic hazard at study sites, it was simulated a set of scenarios using a stochastic summation methods of small-earthquakes records, considered as Empirical Green's Function (EGFs). As Engineering Demand Parameter (EDP), the absolute value of the maximum block rotation normalized by the body slenderness, as a function of the peak ground acceleration (PGA) is adopted. The results show that anchorages are more efficient for blocks with slenderness ratio between two and three, while slenderness above four provide a better stability when they are not restrained. Besides, there is a range of peak intensities where anchored blocks located in soft soils are less vulnerable with respect to those located in firm soils. The procedure used in here allows to take decisions about risk, reliability and resilience assessment of different types of contents, and it is easily adaptable to other seismic environments.

• 공업화학
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• 제7권2호
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• pp.215-220
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• 1996

1-(2-hydroxyethyl)-2-undecyl-2-imidazoline로부터 유도된 9종의 양쪽성 계면활성제에 대한 표면장력과 등전점을 일정농도의 수용액에서 비교 검토하였고, 표면장력법에 의하여 cmc를 추정하였다. 카르복시화 아미드류의 표면장력은 $4.0{\times}10^{-4}{\sim}1.0{\times}10^{-3}mol/{\ell}$ 농도범위에서 26~40dyne/cm, 술폰화 또는 황산화 이미다졸린류는 $1.5{\times}10^{-3}{\sim}2.5{\times}10^{-3}mol/{\ell}$ 농도범위에서 30~35dyne/cm, 술폰화 아미드류는 $5.8{\times}10^{-4}{\sim}8.0{\times}10^{-4}mol/{\ell}$ 농도범위에서 25~33dyne/cm이었다. 또한 등전점의 pH 범위는 카르복시화 아미드류는 pH 7.2~7.9, 술폰화 또는 황산화 이미다졸린류와 술폰화 아미드류는 pH 4.5~5.5이었다.

• 비파괴검사학회지
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• 제19권4호
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• pp.277-287
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• 1999

탄소섬유 복합재료 T 조인트 시험편에 대한 접착특성 및 파손과정을 조사하기 위하여 단순인장 및 하중-제하 인장시험이 수행된다. 시험편은 스킨과 프레임 구조를 가지며, 동시성형과 2차 접착법에 의한 두 종류의 시험편이 제작된다. 단순인장시험동안 시험편의 손상 개시 및 진전시에 AE 특성을 측정하였고, 하중-제하 인장시험동안 진전된 균열길이는 CCD 카메라를 이용하여 측정된다. 또한 시험편 내부의 크랙면 윤곽에 대한 조사는 초음파 C-scan이 사용된다. AE 신호가 급격히 증가하는 하중과 하중-시간 곡선에서 하중강하점은 5% 이내의 오차로 비교적 잘 일치한다. 두 종류의 시험편의 초기균열은 동일한 위치인 중앙 누들부에서 발생되나 최종파단은 동시성형의 경우, 누들부에서, 2차 접착의 경우, 스킨/프레임 끝단에서 일어난다. 이런 결과로부터 두 종류의 시험편은 성형방법에 따라 서로 다른 파손 모드를 보인다.

• 수산해양기술연구
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• 제26권2호
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• pp.111-117
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• 1990

스프링강으로 만든 3가지 크기의 타원형후크에 대하여 만능시험기로 특성시험을 하고, 나팔관을 사용한 통발 자동분리기로 모릿줄의 고달이에 연결된 타원형후크에서 장어통발이 분리되도록 하는 실험을 육상과 해상에서 각각 시행한 경과는 다음과 같다. 1. 직경 3.1mm인 대형의 타원형후크에서 줄의 이탈장력은 60kg 정도이고, 줄을 끼워넣기 위한 손누름 압축력은 6kg 정도이며, 나팔관을 통과장력은 11~15kg 정도였다. 2. 현측 로울러의 앞쪽이나 뒤쪽에 나팔관을 부착한 자동분리기를 사용하여 대형후크에서 통발이 자동으로 분리되도록 하는 육상실험의 결과 양승속도 2~4m/sec에서 분리율은 99%정도였다. 3. 현측 로울러의 후방 2m 정도 되는 곳에 나팔관을 설치하고 대형후크로 해상 시험조업을 한 결과 양승속도 3~4m/sec에서 통발의 분리율은 97%정도였다.

• 대한의생명과학회지
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• 제8권3호
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• pp.143-154
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• 2002

The effect of cardiopulmonary bypass (CPB) on cerebral physiology during heart surgery remains incompletely understood. This study was carried out to investigate changes of cerebral metabolism and the association between the changes and clinical factors during heart surgery. Seventy adult patients (n=70) scheduled for elective cardiac surgery were participated in the present study. Middle cerebral artery blood flow velocity (V$_{MCA}$), cerebral arteriovenous oxygen content difference (C(a-v)O$_2$), cerebral oxygen extraction (COE), and modified cerebral metabolic rate for oxygen (MCMRO$_2$) were measured during six phases of the operation; Pre-CPB, CPB-10 min, Rewarm-1 (nasopharyngeal temperature 34$^{\circ}C$), Rewarm-2 (nasopharyngeal temperature 37$^{\circ}C$), CPB-off, and Post-OP (at skin closure after CPB-off). Each relationship of age, arterial blood gas parameters, or other variables to V$_{MCA}2$, C(a-v)O$_2$, COE, or MCMRO$_2$ was evaluated. V$_{MCA}$ increased (P<0.0001) whereas C(a-v)O$_2$ decreased (P<0.01) throughout the five phases of the operation compared to Pre-CPB value (control). COE diminished at CPB-10, Rewarm-1, and CPB-off (P<0.05) while MCMRO$_2$ reduced at CPB-10 and Rewarm-1 (P<0.05) compared to Pre-CPB value. Positive correlation was found between age and cerebral metabolic parameters (V$_{MCA}$, C(a-v)O$_2$, COE, or MCMRO$_2$) during CPB (range r=0.24 to 0.38, p<0.05). Four cerebral metabolic parameters had partially negative or positive correlation with arterial blood gas parameters and other variables (arterial blood pH, $O_2$ tension, $O_2$ content, $CO_2$ tension, blood pressure, blood flow, temperature, or hematocrit) during the operation. In conclusion, CPB led to marked alterations of cerebral metabolism and age, pH, and $CO_2$ tension profoundly influenced the changes during cardiac surgery.

• 한국공간구조학회논문집
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• 제2권3호
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• pp.81-92
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• 2002

The objective of this paper is to help to make decision of the appropriate structural types in long span structured building due to range of span. For the intention, based on 7 forces of structural element, it is analized the relationships among 6 configurations of structural element(d/1), 25 structural types, 4 materials, and span-length known with 186 sample from 1850 to 1996. 1) bending forces: $club(1/100{\sim}1/10),\;plate(1/100{\sim}1/10),\;rahmen(steel,\;10{\sim}24m)\;simple\;beam(PC,\;10{\sim}35m)$ 2) shearing forces: $shell(1/100{\sim}1/1000)\;hyperbolic\;paraboloids(RC,25{\sim}97m)$ 3) shearing+bending forces: plate, folded $plate(RC21{\sim}59m)$ 4) compression axial forces: club, $arch(RC,\;32{\sim}65m)$ 5) compression+tension forces: shell, braced dome $shell(RC,\;40{\sim}201m),\;vault\;shell(RC,\;16{\sim}103m)$ 6) compression+tension axial forces: $rod(1/1000{\sim}1/100)$, cable(below 1/1000)+rod, coble+rod+membrane(below 1/1000), planar $truss(steel,\;31{\sim}134m),\;arch\;truss(31{\sim}135m),\;horizontal\;spaceframe(29{\sim}10\;8m),\;portal\;frame(39{\sim}55m),\;domical\;space\;truss(44{\sim}222m),\;framed\;\;membrane(45{\sim}110m),\;hybrid\;\;membrane\;(42{\sim}256m)$ 7) tension forces: cable, membrane, $suspension(60{\sim}150m),\;cable\;\;beam(40{\sim}130m),\;tensile\;membrane(42{\sim}136m),\;cable\;-slayed(25{\sim}90m),\;suspension\;membrane(24{\sim}97m),\;single\;layer\;pneumatic\;structure(45{\sim}231m),\;double\;layer\;pneumatic\;structures(30{\sim}44m)$

• 비파괴검사학회지
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• 제26권5호
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• pp.285-290
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• 2006

고장력볼트의 체결상태를 평가하는 것은 체결볼트의 안전유지관리 측면에서 매우 중요하다. 본 논문에서는 초음파의 음속이 응력에 의존하는 이른바 음탄성효과에 기초하여 초음파의 전파시간(TOF)를 측정함으로써 볼트에 작용하는 축응력을 평가하는 방법을 제안한다. 그런데 일반적으로 볼트체결시 볼트에 작용하는 응력범위내에서의 음속 변화량은 매우 작으며, 따라서 TOF 측정에 있어서 높은 정밀도가 요구된다. 이를 위해 본 논문에서는 톤버스트파형의 초음파를 이용한 위상검출법을 적용하였다. 제안된 원리는 실험을 통해 검증되었으며, 볼트 축응력 측정의 유효성을 검증하기 위해 스트레인게이지를 이용한 축응력 측정결과와 비교하였다. 두 결과는 양호한 일치를 보였으며, 이로써 제안한 방법이 체결된 고장력볼트의 체결상태 평가에 유용하다는 결론을 얻을 수 있었다.