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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.
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.
남영현(Young Hyun Nam) 대한기계학회 2008 大韓機械學會論文集A 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 ㎒ and 4 ㎒ 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.
남영현(Young Hyun Nam) 대한기계학회 2008 大韓機械學會論文集A Vol.32 No.7
This paper describes a synthesized photoelastic method developed for the visualization and evaluation of sound pressure distribution of elastic wave in a solid. The visualization of wave stress field is achieved by synthesizing two photoelastic pictures, in which the direction of the principal axis of linear polariscopes differs by 45?˚. From the analysis of the wave stress distribution using this method, it is possible to evaluate the characteristics of elastic waves in a solid, such as the intensity of stress, directivity and resolution characteristics of the wave emitted from a commercial probe, and characteristics of scattering from various types of defects.
초음파에 의한 알루미늄 소결체 설계를 위한 탄성계수 예측
남영현(Young Hyun Nam) 대한기계학회 2008 大韓機械學會論文集A Vol.32 No.7
The ultrasonic velocities of sintered aluminum with varying density were measured in order to deduce the mechanical properties for optimum design of the sintered aluminum. Specimens with different densities were prepared by the plasma activated sintering machine. The density distribution of sintered aluminum becomes partially inhomogeneous because of the friction between the powder and the die during compaction. The elastic moduli are increased as the ultrasonic velocity is increased. Furthermore, Poisoon's ratio is depending on not only the density but also the size and distribution of voids. As the specimen’s thickness increases, the center frequency in the frequency spectrum of the reflection wave is shifted to the low frequency. The attenuation coefficient of ultrasonic wave is decreased inversely as the density increased.
등온열처리에 따른 2.25Cr-1Mo강의 초음파 특성 변화
남영현(Young-Hyun Nam),백운봉(Un-Bong Baek),박종서(Jong-Seo Park),남승훈(Seung-Hoon Nahm) 대한기계학회 2013 大韓機械學會論文集A 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.