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단일 센서와 공간집속 신호처리 기술을 이용한 복합재 판에서의 충격위치 결정
조성종(Sungjong Cho),정현조(Hyunjo Jeong) 한국소음진동공학회 2012 한국소음진동공학회 학술대회논문집 Vol.2012 No.10
A structural health monitoring (SHM) technique for locating impact position in a composite plate is presented in this paper. The technique employs a single sensor and spatial focusing properties of time reversal (TR) and inverse filtering (IF). We first examine the focusing effect of back-propagated signal at the impact position and its surroundings through simulation. Impact experiments are then carried out and the localization images are found using the TR and IF signal processing, respectively. Both techniques provide accurate impact location results. Compared to existing techniques for locating impact or acoustic emission source, the proposed methods have the benefits of using a single sensor and not requiring knowledge of material properties and geometry of structures. Furthermore, it does not depend on a particular mode of dispersive Lamb waves that is frequently used in the SHM of plate-like structures.
단일 센서와 공간집속 신호처리 기술을 이용한 복합재 판에서의 충격위치 결정
조성종(Cho, Sungjong),정현조(Jeong, Hyunjo) 한국소음진동공학회 2013 한국소음진동공학회 논문집 Vol.23 No.2
A structural health monitoring(SHM) technique for locating impact position in a composite plate is presented in this paper. The technique employs a single sensor and spatial focusing properties of time reversal(TR) and inverse filtering(IF). We first examine the focusing effect of back-propagated signal at the impact position and its surroundings through simulation. Impact experiments are then carried out and the localization images are found using the TR and IF signal processing, respectively. Both techniques provide accurate impact location results. Compared to existing techniques for locating impact or acoustic emission source, the proposed methods have the benefits of using a single sensor and not requiring knowledge of material properties and geometry of structures. Furthermore, it does not depend on a particular mode of dispersive Lamb waves that is frequently used in the SHM of plate-like structures.
초음파 펄스-에코 측정을 통한 열화 시편의 음향 비선형 특성 평가
조성종(Sungjong Cho),정현조(Hyunjo Jeong),신효정(Hyojeong Shin),주영상(Young Sang Joo) 한국소음진동공학회 2019 한국소음진동공학회 논문집 Vol.29 No.3
An experimental study was conducted to accurately measure the absolute nonlinear parameter (β) of damaged solid samples in a pulse-echo setup; the results are presented in this paper. Artificially aged Al 6061 specimens were used as the damaged specimens. To improve the amplitude of the second harmonic wave received in the pulse-echo mode with a stress-free boundary to a measurable level, we developed a dual element transducer in which the transmitter and receiver were separated. To measure absolute β, the transfer function was determined from the calibration experiment of the receiving transducer, and diffraction and attenuation corrections were made. The results of β measurement were presented as a function of the aging time, and the change in β were found to well represent the variation in the microstructure of the material owing to the change in precipitate.
회절과 감쇠를 고려한 두꺼운 고체 시편의 비선형 파라미터 측정
조성종(Sungjong Cho),정현조(Hyunjo Jeong),장수증(Shuzeng Zhang) 한국비파괴검사학회 2017 한국비파괴검사학회지 Vol.37 No.4
재료의 손상 상태나 미시적 특성을 나타내는 정량적인 지표로서 비선형 파라미터 β가 자주 사용되고 있다. 원칙적으로 β 값은 1차원 평면파가 비선형 매질을 전파할 때 발생하는 기본파 변위와 제2차 고조파 변위를 측정함으로써 구할 수 있다. 하지만 실제 실험에서는 파동의 전파 및 수신 과정에서 빔의 회절과 감쇠 현상이 수반된다. 최근까지의 연구 결과를 보면 회절 효과를 무시하기 위해 대부분 근거리 음장 내에서 β가 측정되었다. 회절 효과를 무시하기 위해서는 탐촉자의 형상, 입력 주파수, 시편의 두께 등에 대한 제한이 따른다. 이러한 제한이 없는 실용적인 β 측정 기술에 대한 연구가 필요하다. 이에 본 논문에서는 두께 4 cm ~ 12 cm의 알루미늄 시편에 대하여 유한진폭법으로 β를 측정하고, 회절 및 감쇠 효과가 측정값에 미치는 영향을 체계적으로 연구하였다. 정확한 β 측정을 위해서는 회절 및 감쇠에 대한 올바른 보정이 모두 필요함을 확인하였고, 이 경우 전 시편에 걸쳐 약 4% 이내로 일치하는 β값을 얻을 수 있었다. The nonlinearity parameter β is commonly used as an important indicator of damage state and microstructural characteristics. This parameter can be obtained by measuring the fundamental and second harmonic wave displacements when a one-dimensional plane wave propagates in the nonlinear medium. However, in a real experimental situation, beam diffraction and medium attenuation always appear during propagation and reception. Most of the previous studies ignored these effects by restricting the β measurements in the near field. In the present study, 4- to 12-cm-thick solid samples were prepared, and β measurements were made using the finite amplitude method. The effects of diffraction and attenuation corrections on the β values were then systematically investigated. The agreement of β between different-thickness samples when diffraction and attenuation corrections were all properly made was better than 4%.