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Variable Angle Beam Guided Wave Probe Design for Tubing Based on Solid Mechanics
Cho, Younho 한국비파괴검사학회 2003 한국비파괴검사학회지 Vol.23 No.6
A State-of-art methodologies on implementing conventional piezoelectric and flexible PVDF elements for generating ultrasonic guided waves in a tubing are presented. Comb transducers with PVDF can be efficiently applied to selectively excite a guided wave mode by wrapping around any size pipe while a conventional immersion type piezo-elements can be also possibly used with a modification of transducer fabrication. Technical comparisons between the use of angle beam probe and comb one will be also discussed in detail. The presented technique can be easily applied to NDE for a long range inspection of tubular structures.
조윤호(Younho Cho),이재선(Jaesun Lee),정경식(Kyoungsik Jeong) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
Material properties of lock plate which cover gas turbine blade are studied using ultrasonic guided waves. Lock plate which are mostly imported is a very important part of gas turbine. Measuring wave velocity and attenuation coefficient are used to investigate material properties of three different heat treatment conditions. Tensile and fatigue test results are compared with guided waves signal analysis on the Inconel x-750 material properties. Wave velocity and hardness of Inconel x-750 are proportionately related each other. This measurement of material properties can be used for broad industrial area to make sure life of material to prevent accident.
감육부에 대한 SH파 진단 정량화 및 가시화를 위한 연구
조윤호(Younho Cho),Yunri Piao,신봉재(Bongjea Sheen),현승호(Seungho Hyun) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11
It is important to ensure the reliability of industrial facilities which are subjected to aging due to exposure to high temperature and high pressure environment. The eroded part in pipe line due to wall thinning needs to be assessed by applying special nondestructive inspection techniques which are widely used in order to evaluate the structural integrity. This can be achieved through the signal characteristic which also contains scattered information due to wall thinning. This paper will present the modeling for long-range scattering field of shear horizontal (SH) waves of eroded plates with Boundary Element Method (BEM) to predict the behavior of SH wave and to improve the reliability of the detection result. Moreover, with the comparison through transmission and reflection coefficient for different size of depth and width of the defect, we can evaluate the sensitivity of the SH wave mode. BEM formulation is performed in frequency domain, and then time domain's signal of BEM result will be compared with the experimental waveform in time domain. The finally, the quantification via imaging of wall thinning with reconstruction algorithm for the Probabilistic inspection of damage (RAPID) is accomplished. From this study, it is found that there is a good agreement of modeling result with experimental one.
실시간 진단을 위한 산재형 센서네트워크의 토모그래피 연구
조윤호(Younho Cho),박운일(Yunri Piao),신봉재(Bongjae Sheen),김련희(Lianji Jin),안봉영(Bongyoung Ahn),조승현(Seunghyun Cho) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
There has been much interest recently about the on-line structural health monitoring in plate-like structures using guided wave. The guided wave mode conversion phenomenon under through transmission scheme is simulated by the hybrid BEM and employed as a useful feature for defect location. The work presented here introduces a Reconstruction Algorithm for the Probabilistic Inspection of Damage (RAPID) which is used to construct tomographic images of defect. Through this study, we found a feasibility of defect image reconstruction based on the BEM modeling ad the tomograpy of guided waves.
조윤호(Younho Cho),정경식(Kyungsik Jung),이재선(Jaesun Lee) 대한기계학회 2010 大韓機械學會論文集A Vol.34 No.6
가스터빈 날개를 덮고 있는 덮개판(Lock plate)의 재료 물성을 유도초음파를 이용하여 측정을 하였다. Lock plate는 가스터빈 발전소에서 아무 극한 환경에서 작동을 하는 부분 중 하나이다. 초음파 속도와 감쇠계수가 서로 다른 3가지 조건의 열처리상태의 재료 물성을 측정하는데 사용되었다. 일반적인 기계적 파괴 인장 실험과 비교했을 때, 인코넬 x-750의 재료특성은 다른 열처리 조건에서 탄성계수와 포아슨비를 활용하여 비파괴적인 방법으로 더 효과적으로 알아냈다. 초음파 속도와 인코넬 x-750의 강도는 서로 비례관계에 있으며, 이러한 재료물성 측정은 여러 산업 분야에서 손상 측정에 활용될 수 있다. 또한 유도초음파 기법을 활용하여 장거리, 광범위한 진단으로 시간과 비용을 절감하는데 도움이 되리라 기대된다. Material properties of the lock plate, which covers the gas-turbine blade, are studied using ultrasonic guided waves. The lock plate is a crucial part of a gas-turbine power plant. The wave velocity and attenuation coefficient are measured to investigate the changes in the material properties under three heat-treatment conditions. Compared to the destructive mechanical tests, the material characterization of Inconel X-750 can be performed more efficiently and nondestructively by using ultrasonic guided waves; this characterization helps identify the changes occurring in its elastic moduli and Poisson's ratio under different heat-treatment conditions. The wave velocity and hardness of Inconel X-750 are proportional to each other. This nondestructive technique for the measurement of material properties can be widely used in various industries to avoid catastrophic failure. It is also expected that the guided-wave technique can be applied as a new cost- and time-saving inspection tool for longer and wider inspection ranges.
조윤호(Cho Younho),이준현(Joon-Hyun Lee),김문생(Moon-Saeng Kim) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
본 연구에서는 반도체나 MEMS형 소재에 많이 응용되는 박형(plate-like thin film)재료의 두께 및 물성 측정에 활용이 가능한 램형 탄성파모드의 응용기법이 소개된다. 박형금속재료내 탄성파 모드분석을 위한 분산곡선이 소개되며, 탄성파 모드의 분산성과 속도변화를 이용한 두께 및 물성 측정의 실험적 기법이 제안된다. 박형재료내의 물성과 두께변화는 특정 탄성파모드의 속도변화에 민감한 의존성을 나타내게 되며 이 같은 주파수의존재성은 저주파대역의 기본 모드에서 더욱 크게 나타남을 확인할 수 있었다. 향후 본 연구의 결과는 다양한 나노/MEMS소재의 공정에 대한 실시간 모니터링 기법으로 활용될 수 있을 것으로 기대된다.