전자기법을 이용한 3Cr-lMo-0.25V 강의 물성 평가

남영현,안봉영,이승석,Nam, Young-Hyun,Ahn, Bong-Young,Lee, Seung-Seok 대한기계학회 2003 大韓機械學會論文集A Vol.27 No.2

It is advantageous to use NDE methods to assess the mechanical properties of materials since the conventional method is time-consuming and sometimes requires cutting of sample from the component. The NDE parameters such as ultrasonic velocity and attenuation, electric resistivity, and magnetic coercive force and remanance have been utilized to evaluate changes of material properties due to heat treatment condition. It has been found that changes of materials properties under quenched and tempered/PWHT treatments could not be detected using EMAT and Electrical resistivity methods. However, victors hardness and magnetic hysteresis loop decreased with heat treatment procedures. These results were obtained using 3Cr-lMo-0.25V steel. The magnetic parameters were found to be most sensitive to changes of material properties.

국민을 나침반으로 K-Water가 만들어 가는 물관리 혁신

남영현 한국서비스경영학회 2022 한국서비스경영학회 학술대회 Vol.2022 No.11

탐촉자와 표면 결함에 대한 지향성의 수치 실험에 관한 연구

남영현 韓國非破壞檢査學會 1995 한국비파괴검사학회지 Vol.15 No.1

초음파 검사는 초음파가 한 방향으로 진행한다고 하는 지향성을 이용하고 있으며, 지향성은 초음파의 전파방향 및 음압분포의 관계를 나타내고 있다. 본 논문에서는 가시화법을 적용하여 사각탐촉자로부터 방사되고, 표면결함으로부터 산란한 횡파의 지향성을 조사하고, 이런 실험결과들을 연속파를 기초로 한 기존 이론과 비교하였다. 연속파이론의 적용성이 d/λ의 변수로 고찰되었다.(d는 진동자 및 결함의 크기, λ는 파장) 사각탐촉자의 경우, 실험결과들은 주극에서 이론적으로 계산한 지향성과 잘 일치하고 있었으며, 결함의 크기가 파장보다 작은 경우에도, 반사파에는 명확한 지향성이 관찰되었다. 파장에 대한 결함의 크기의 비가 동일할 때 결함으로부터 반사파의 지향성은 주파수의 차이에도 불구하고 거의 일치하였다. d/λ가 1.5 이상일 때 측정한 지향성들은 이론적으로 계산한 지향성과 거의 동일하였다. An ultrasonic testing uses the directivity of the ultrasonic wave which propagates in one direction. The directivity is expressed as the relationship between the propagate direction and its sound pressure. This paper studied the directivity of shear wave emitted from angle probes and scattered from surface defects by using visualization method. These experimental results were compared with the theory which was based on the continuous wave. The applicability of continuous wave theory was discussed in terms of the parameter d/λ; where d is transducer or defect size and λis the wavelength. In the case of angle probes, the experimental results show good agreement with theoretical directivity on the principal lobe. When defect size was smaller than the wavelengths, clear directivity in the reflected wave was observed. In the case of the same ratio of defect size to wavelength, the directivity of reflected waves from the defect show almost the same directivity in spite of frequency differences. When the d/λis greater than 1.5, measured directivities almost agreed with the theoretical one.

초음파에 의한 압력용기의 연취성천이온도 평가

남영현 한국비파괴검사학회 2000 한국비파괴검사학회지 Vol.20 No.5

파괴적인 방법으로 재료나 설비의 기계적 성질을 평가하기 위해서는 많은 경비와 시간이 소요되므로 비파괴적인 방법을 이용한 재료의 기계적 성질 평가가 주목을 받고 있다. 본 논문에서는 초음파 특성을 이용하여 열처리 온도와 조건에 따른 기계적 성질 변화를 평가하였다. 초음파의 감쇠계수는 열처리 온도가 높을수록 결정립의 크기가 커지므로 증가하였다. 초음파의 감쇠계수는 열처리(담금질, 탬퍼링, 용접후열처리)가 진행됨에 따라 감소하였다. 초음파 속도는 담금질과 탬퍼링/PWHT한 시편에서 40㎧의 차이를 보이고 있었다. 감쇠계수와 인성과의 상관성은 매우 좋으며 이러한 상관관계는 단조한 압력용기의 비파괴 평가에 이용할 수 있으며, 더욱이 현장 적용에 효율적으로 응용할 수 있을 것이다. It is useful to use NDE methods to assess the mechanical properties of materials since destructive methods are time-consuming and usually require cutting of sample from the material/component, In the present research, ultrasonic characteristics have been utilized to evaluate changes of mechanical properties due to heat treatment because the grain size increased in size as the temperature. The attenuation coefficient decreased as the heat treatment has been progressed (quenched, tempered, PWHT). In the case of ultrasonic velocity measurement, velocity measurement, velocity difference between quenched and tempered/PWHT was 40 m/s. There was a good relationship between the attenuation coefficient and the toughness. The relationship can be used for the nondestrucitve evaluation of the forged reactor vessels. Moreover, the method may be effectively used in the field application.

초음파의 파형 해석에 의한 고감쇠 재료의 평가

남영현 韓國非破壞檢査學會 1995 한국비파괴검사학회지 Vol.15 No.2

본 논문은 초음파법을 이용하여 소결 재료의 비파괴적인 평가 방법을 확립하는데 목적을 두고 있다. 소결 재료의 밀도는 소결체로 제작되는 동안 금형과 분말사이의 마찰 때문에 부분적으로 불균질한 분포를 가지고 있으며 이 불균질성은 에너지 감쇠 계수 및 초음파 반사 에코의 주파수 스펙트럼에 있어 중심 주파수의 변화량에 의해 조사되었다. 초음파의 속도, 탄성계수, 포와송 비는 소결 재료의 밀도와 비례 관계에 있었으며 저면 반사파의 중심 주파수는 초음파의 전파 거리의 증가 및 밀도의 감소에 따라 저주파수 쪽으로 이동하였으나 에너지 감쇠 계수는 밀도의 증가에 따라 감소하고 있었다. 본 논문에서는 반사파의 주파수 스펙트럼에 있어 중심 주파수의 변화가 소결 재료의 비파괴적인 평가 방법으로써의 가능성을 보여주고 있다. The purpose of this paper was to develop a nondestructive evaluation method of sintered material by ultrasonic method. The density distribution of sintered material becomes inhomogeneous partially because of the friction between the powder and the die during compaction. The inhomogeneity was investigated by measurement of the energy attenuation coefficient and the shift of the center frequency in the frequency spectrum of the ultrasonic reflection echo. The experimental results showed that the center frequency of reflection wave depended linearly on the density of sintered materials. However, the attenuation coefficient decreased inversely as the density increased. This study shows that the shift of the center frequency in the frequency spectrum of reflection wave can be used to a nondestructive evaluation of sintered materials.

등온열처리에 따른 2.25Cr-1Mo강의 초음파 특성 변화

남영현,백운봉,박종서,남승훈,Nam, Young-Hyun,Baek, Un-Bong,Park, Jong-Seo,Nahm, Seung-Hoon 대한기계학회 2013 대한기계학회논문집 Vol.37 No.3

본 논문은 등온열처리 온도 및 시간에 따른 2.25Cr-1Mo강의 초음파 특성 변화를 조사하였다. Charpy 충격시험과 경도시험이 3종류의 열처리조건을 가지는 각 시편들에 대하여 실시되었다. 종파를 이용한 펄스-에코법이 초음파의 감쇠와 속도 측정에 사용되었다. 연취성천이온도(FATT)는 등온열처리 시간이 길어짐에 따라 증가하였는데, 이는 인성이 감소되고 있음을 의미한다. 등온열처리 시간과 온도의 증가와 함께 종파의 속도 및 초음파의 감쇠계수는 증가하였다. The ultrasonic characteristics of 2.25Cr-1Mo steel were investigated in relation to the isothermal heat treatment temperature and time. Charpy impact tests and hardness tests were conducted on individual specimens with three different heat treatment conditions. A pulse-echo method with longitudinal waves was used to measure the attenuation and velocity of ultrasonic waves. The FATT (fracture appearance transition temperature) increased with an increase in the isothermal heat treatment time, which implies that the toughness decreased. As the isothermal heat treatment time and temperature increased, the longitudinal wave velocity and ultrasonic attenuation coefficient were raised.

[그리움이 묻어나는 편지] 그 누구보다 당신을 사랑합니다. 어머니!

남영현 샘터사 2001 월간 샘터 Vol.32 No.6

맞대기 용접부내의 인공 결함에서 초음파의 전파특성

남영현 대한용접접합학회 1996 대한용접·접합학회지 Vol.14 No.6

An ultrasonic testing uses the directivity of the ultrasonic wave which propagates in one direction. The directivity is expressed as the relationship between the propagate direction and its sound pressure. The directivity of ultrasonic wave is related to determination of testing sensitivity, scanning pitch and defect location. This paper investigated the directivity of ultrasonic wave, which scattered from slit defect located in heat-affected zone (HAZ) in butt joint using visualization method. The directivity of shear waves scattered from slit defect were different according to probe direction (far defect, near defect) and probe position (forward movement, maximum echo position, backward movement). The difference of directivity of reflection wave was existed between 2 MHz and 4 MHz angle probes. In the case of 2 MHz angle probe, the directivity of reflection wave was appeared sharp form because of the relation wave length and defect size.

스타트업 특성이 혁신역량에 미치는 영향 연구 - 공기업과의 협력관계를 중심으로

남영현,서영욱 한국지식정보기술학회 2020 한국지식정보기술학회 논문지 Vol.15 No.2

The role of startups is being highlighted as a way to cope with rapid changes of business environment. The core of startups embraces technical innovation and agility, and their role in the related industries will be stressed further in line with the Fourth Industrial Revolution. This study aims to review the factors which impact innovation capability from two aspects. Firstly, the innovation capability which socialization process and relationship learning between startups and public enterprises impact have been studied in a perspective of social exchange theory, and how the internal property of startups affects innovation capability with absorptive capacity has been reviewed thereafter. To this end, this study covers an empirical analysis by conducting a questionnaire focused on startups which have experienced the cooperation with Korean public enterprises, and it is assured that six hypotheses proposed were entirely adopted. Their implications are as follows. This study shows the socialization process, which the active discussion has been insufficient in the business-to-business studies, and presents that factors of relationship learning between startups and public enterprises could have positive impacts on the absorptive capacity of startup internal members.

초음파 사각 트랜스듀서의 최적설계를 위한 지향성 해석

남영현,Nam, Young-Hyun 대한기계학회 2008 대한기계학회논문집 Vol.32 No.9

Ultrasonic testing uses the directivity of the ultrasonic wave, which propagates in on direction. The directivity is expressed as the relationship between the propagate direction and its sound pressure. The directivity of an ultrasonic wave is related to the choice of probe arrangement, testing sensitivity and scanning pitch and correct measurement of defect size and location. This paper describes on the directivity measurement of ultrasonic wave using the visualization method. The directivity of shear wave emitted from the angle beam transducer were constant during propagation. The difference of directivity was existed between 2 MHz and 4 MHz angle beam transducers. When these experimental results were compared with the theory which was based on the continuous wave, it showed good agreement with theoretical directivity on the principal lobe.