FMC/TFM에 기반한 배플포머볼트 위상배열 초음파 검사 기술 개발 = Development of Phased Array Ultrasonic Testing Technique Based on FMC/TFM for Baffle-Former Bolts

국문 초록 (Abstract)

외부 육각 볼트 머리 형태의 배플포머볼트에 대한 체적검사는 일반적으로 2개의 압전소자를 가지는 초음파 탐촉자가 lock-bar 양측의 볼트의 머리 부분에 접촉하고 볼트의 중심부로 향하는 6도의 굴절 종파를 발생시켜 수행된다. 이러한 탐촉자는 고정된 위치에서 한 각도의 초음파로 검사를 수행하기 때문에 검사 성능이 제한된다. 위상배열 초음파 기술 적용은 이러한 제한사항을 극복하고 배플포머볼트 초음파 검사 신뢰성을 향상시킬 수 있다. 하지만 기존의 상용 위상배열 초음파 장치에서는 탐촉자의 분리된 압전소자 그룹에 대해서는 lock-bar 하단의 위치한 결함 탐지에 유용한 피치캐치 모드 초음파 이미지 생성이 불가하다는 한계를 가지고 있다. 이번 연구에서는 배플포머볼트 검사를 위해 Full Matrix Capture (FMC)와 Total Focusing Method (TFM)에 기반한 위상배열 초음파 검사 기술을 개발하였다. 제안된 기법을 통해 피치캐치 모드에 대한 초음파 이미지를 합성할 수 있었고, 다양한 모드의 TFM 이미지는 배플포머볼트의 다양한 위치의 결함을 지시하고 평가함에 있어 유용하게 적용할 수 있음을 검증하였다.

다국어 초록 (Multilingual Abstract)

Conventional volumetric inspection of bolts of an external hexagon bolt-head type was performed using an ultrasonic probe with two piezoelectric elements that contact the bolt head on each side of the lock-bar and generate a 6 degree refracted longitudinal wave towards the centerline of the bolt. The inspection performance of the probe is limited because the inspection is implemented with a single-angle refracted wave at a fixed position. The application of phase-array ultrasonic technology to baffle-former bolts can overcome these limitations and improve the reliability of the ultrasonic inspections of these bolts. However, existing commercial phase array ultrasonic instruments have a limitation that they cannot generate an ultrasonic image of pitch-catch mode useful for detecting defects underneath the lock-bar for separated elements group of the probe. In this study, we developed a phase-array ultrasonic inspection technique based on Full Matrix Capture (FMC) and Total Focusing Method (TFM) for baffle-former bolt inspection. Using the proposed technique, we verified that it is possible to reconstruct ultrasonic images for the pitch-catch mode and that the TFM images in various modes are helpful for detecting and evaluating defects in different locations of the baffle-former bolts.

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