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매설형 자기변형 초음파 트랜스듀서를 이용한 고온 구조물 두께 감시
허태훈(Taehoon Heo),조승현(Seung Hyun Cho) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12
Wall thinning is one of severe problems of the secondary piping systems in nuclear power plants, so it is very essential to monitor the thickness of the pipe periodically. However, the monitoring in operation is very difficult to execute due to high temperature about to 270 degrees Celsius and thick insulating layers. This work presents a thickness monitoring method using an embedded magnetostrictive transducer which comprises an Fe-Co element, a PCB coil, and bias magnets. It was designed to be installed under insulating layers since it has considerably thin structure less than 5 mm. It can endure over 300 degrees Celsius since magnetostriction of Fe-Co occurs well during temperature region. Also a portable pulser/receiver was developed to operate the transducer. The present method was verified through experiments with high temperature specimens and shows successful results to detect the thickness of the structure.
전자기 음향 공진을 이용한 강선의 표면 미세 결함 탐상 타당성 연구
허태훈(Taehoon Heo),조승현(Seung Hyun Cho),안봉영(Bongyoung Ahn),임종수(Zhong Soo Lim) 한국비파괴검사학회 2013 한국비파괴검사학회지 Vol.33 No.1
철강 생산 제품 중 강선 (steel wire rod)은 제조 과정 중 종방향으로 미세한 표면 결함이 매우 빈번하게 발생하는데 이중 깊이가 수 십 마이크로미터 이상인 결함들은 최종 생산품의 불량을 유발하는 심각한 원인이 되고 있다. 이와 같은 이유로 강선의 제조 단계에서 표면의 미세 결함의 깊이를 평가하는 방법의 개발이 절실히 요구된다. 표면 미세 결함을 평가할 수 있는 여러 가지 방법 중에서, 본 연구에서는, 전자기 음향 공진법의 적용 가능성을 고찰하고자 한다. 전자기 음향 공진 (electromagnetic acoustic resonance, EMAR)은 전자기 음향 트랜스듀서 (electromagnetic acoustic transducer, EMAT)을 이용하여 시편의 공진 특성을 측정하는 방법으로서, 대상의 작은 변화에도 민감하게 반응하고 비접촉 측정이 가능하여 현장 적용에 용이하다는 장점이 있다. 전자기 음향 공진 실험을 통하여 표면 미세결함과 잔향특성의 변화를 관찰하여 깊이 약 100 마이크로 미터 내외의 결함은 탐상 가능함을 확인하였다. The surface microcrack over a few tens of micrometers is one of severe problems of a steel wire rod to lead to the failure of the final products, so the method to evaluate crack depth has been required to develop. This work investigates the feasibility of electromagnetic acoustic resonance (EMAR) for this problem. EMAR is the method for measurement of resonant features using electromagnetic acoustic transducer (EMAT). Generally, EMAR is sensitive to small variation of the structures and easy to apply it to the industrial field because of the feature of noncontact measurement. Through several EMAR experiments, the change of the resonant frequencies and attenuation in reverberation has been observed. The results confirms that the surface cracks of around 100 micrometer depth can be detected successfully with the present method.
조승현(Seung Hyun Cho),허태훈(Taehoon Heo),지봉규(Bonggyu Ji),안봉영(Bongyoung Ahn),장강원(Gang-Won Jang) 한국소음진동공학회 2014 한국소음진동공학회 학술대회논문집 Vol.2014 No.10
Regarding thin films in MEMS/NEMS structures, the exact evaluation of mechanical properties is very essential to enhance the reliability of their design and manufacturing. However, such methods as a tensile test and a resonance test, general methods to measure elastic moduli, cannot be applied to thin films since its thickness is so small. This work concerns guided wave based elastic modulus measurement method. To this end, guided wave excitation and detection system using a pulsed laser and a laser interferometry has been established. Also an elastic modulus extraction algorithm from the measured guided wave signal was developed. Finally, it was applied to actual thin film structures such as Ni-Si and Al-Si multilayers. From experimental results, we confirm that the proposed method has considerable feasibility to measure elastic properties of thin films.
조승현(Seung Hyun Cho),지봉규(Bonggyu Ji),안봉영(Bongyoung Ahn),박현지(Hyun Ji Park),허태훈(Taehoon Heo) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12
Regarding thin films in MEMS/NEMS structures, the exact evaluation of mechanical properties is very essential to enhance the reliability of their design and manufacturing. However, such methods as a tensile test and a resonance test, general methods to measure elastic moduli, cannot be applied to thin films since its thickness is so small. This work concerns guided wave based elastic modulus measurement method. To this end, guided wave excitation and detection system using a pulsed laser and a laser interferometry has been established. Also an elastic modulus extraction algorithm from the measured guided wave signal was developed. Finally, it was applied to actual thin film structures such as Ni-Si and Al-Si multilayers. From experimental results, we confirm that the proposed method has considerable feasibility to measure elastic properties of thin films.