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.

지속가능 물관리를 위한 ESG와 인공지능

남영현,김성훈,Nam, Yeong-Hyeon,Kim, Seong-Hun 한국수자원학회 2021 물과 미래(한국수자원학회지) Vol.54 No.7

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.

초음파 자동 검사시스템의 개발과 오버레이 용접부의 결함검사

남영현,성운학 한국비파괴검사학회 2000 한국비파괴검사학회지 Vol.20 No.6

발전 및 산업설비에 사용되는 많은 압력용기는 저합금가강을 사용하여 제작되고 있다. 압력용기의 내면은 부식이 미치는 영향을 최소화하기 위하여 오스테나이트계 스테인리스강으로 덧살용접을 하고 있으나, 용접 층간의 계면에서 발생하고 있는 박리균열은 압력용기의 신뢰성에 중요한 변수가 되고 있다. 본 연구에서는 DSP를 사용하여 오버레이 용접부를 고속으로 검사할 수 있는 C-scan 시스템을 개발하였다. 본 시스템은 신호 처리부 (오실로스코프, 펄서.리시버, 디지타이저, DSP), 스케너, 프로그램 및 위치 제어부로 구성되어 있다. 개발된 시스템을 사용하여 실제 오버레이 용접부에 대한 초음파검사를 실시한 결과 고속으로 신뢰성 높은 검사결과를 얻을 수 있었다. Many pressure vessels for power and industrial plant are fabricated from low alloy carbon steels. The inner sides of pressure vessels are commonly weld-cladded with austenitic stainless steels to minimize problems of corrosive attack. Disbonding cracks are often detected at the transition region of welding interlayer, which is serious problem to reliability of pressure vessels. We have developed C-scan system to high speed inspection of overlay weld using DSP(digital signal processor). This system consists of signal processing parts (oscilloscope, pulser/receiver, digitizer, DSP), scanner, program and position controller. The developed system has been applied to a practical ultrasonic testing in overlay Weld, and demonstrated high speed with precision

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.

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.

초음파법을 이용한 연 / 취성천이온도 예측 ( Prediction of Fracture Appearance transition temperature ( FATT ) by Ultrasonic Method )

남영현,성운학,김정태 대한기계학회 1998 대한기계학회 춘추학술대회 Vol.- No.-

초음파와 Barkhausen Noise에 의한 강의 연.취성천이온도 예측

남영현,성운학,Nam, Young-Hyun,Seong, Un-Hak 대한기계학회 1999 大韓機械學會論文集A Vol.23 No.7

It is advantageous to use an NDE method to assess the mechanical properties of materials since the conventional method is time-consuming and sometimes requires cutting of sample from the material/component. This paper shows that the ultrasonic and the Barkhausen noise(BHN) methods can be used to accurately characterize forged reactor vessels. The attenuation coefficient of the ultrasonic wave was changed with heat treatment temperature and condition[as-quenched, tempered, PWHT]. The RMS[root mean square] voltage of Barkhausen noise depended on heat treatment temperature and conditions. The fracture appearance transition temperature(FATT) can be predicted using nondestructive evaluation methods.

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.

충청남도 석면폐광산 기반 석면건강영향조사 분석연구

남영현,이용진,장은철,권순찬,강민성 대한직업환경의학회 2016 대한직업환경의학회 학술대회 논문집 Vol.2016 No.11