Recently, due to advancement in construction techniques, structures are being constructed much faster than before. Therefore, structures such as cable stayed bridges and suspension bridges, must be inspected regularly to assure their main elements (i.e., load carrying cables) are healthy and sound. Structures can be tested using conventional nondestructive testing methods such as magnetic flux leakage (MFL), eddy current testing, acoustic emission and etc. In this study, it was tried to detect cross sectional reduction in steel rod using a time dependent numerical simulation of coil sensor based on MFL principle.

The purpose of this research is to develop nondestructive equipment using magnetic flux leakage(MFL) principle and to confirm the accuracy of the equipment. The equipment consist of a magnetization part, a sensor part, and a data storage part. The parameters of specimens for equipment verification are the length and the area of flaws. It was confirmed that the equipment accurately probed the locations of the flaws in the specimens, and grout had little effect on the results of the test.

열차운행에 따라 철도레일에 반복적으로 가해지는 높은 하중은 레일에 결함을 발생시키게 되며 결함이 진전될 경우 궁극적으로 레일의 파손을 유발할 수 있다. 레일의 파손은 많은 유지보수 비용을 유발시키며 나아가 열차탈선이라는 안전문제와 직결되어 있어 레일의 결함을 조기에 검출할 수 있는 효율적인 비파괴 검사법(NDT)이 필요하다. 특히, 레일과 같이 길이가 매우 긴 연속체 구조물을 효과적으로 검사하기 위해서는 고속탐상을 통한 시간단축이 실용화를 위한 주요 요구조건이 된다. 이에 본 연구에서는 비접촉으로 고속탐상이 가능한 비파괴 검사기술인 누설자속탐상 (Magnetic Flux Leakage, MFL) 기술의 기반으로 철도레일 결함 탐상을 위한 적용 가능성을 검증하였다. 검증은 다양한 위치와 크기를 갖는 5가지 종류의 결함레일 시편에 자체 제작한 MFL 센서를 적용하여 결함검출 가능여부를 확인하는 방법으로 진행하였다. 시험결과 수직 및 대각선 방향의 국부손상에 대해 자속누설 신호가 잘 검출 되었으며 이를 통해 누설자속탐상 기술의 철도레일 적용 가능성을 확인할 수 있었다. 향후 연구를 통해, 철도레일 단면에 최적화된 센서부 제작 및 고속탐상이 가능하도록 신호처리가 이루어진다면 철도레일 국부결함 검출을 위한 매우 효과적인 비파괴 검사법이 될 것으로 기대된다.

In this study, an automated cable non-destructive test (NDT) system was proposed to monitor the steel cable. Magnetic Flux Leakage (MFL) method was applied for the cable inspection. A multi-channel MFL sensor head was fabricated using Hall sensors and permanent magnets. A wheel based Cable climbing robot was used to improve the accessibility to cable. In addition, remote data transmission and robot control were possible by applying the Wireless LAN communication. Finally, developed element techniques were integrated to MFL based Cable Climbing NDT system, and the field applicability of the integrated cable NDT system was verified through a field test.

In this study, an MFL(Magnetic Flux Leakage)-based NDT(non-destructive test) method was applied to detect the inner damages of steel cable. A steel cable bunch specimen with several types of inner damage was fabricated and scanned by a MFL sensor head to measure the magnetic flux density of the specimen.the measured magnetic flux signal was visualized into a 3D MFL image for convenient cable monitoring. Finally, the results were compared with information on actual inflicted damages to confirm the accuracy and effectiveness of the proposed cable monitoring method.

In this study, a MFL (Magnetic Flux Leakage) image based 3D inspection system which is incorporated into a cable climbing robot was investigated for Steel Cable NDT of Cable-stayed Bridge and Suspension Bridge. Firstly, a MFL sensor head prototype composed of two permanent magnets and eight hall sensors was designed and fabricated. A steel cable specimen with several types of damage was inflicted and scanned by the MFL sensor head to measure the magnetic flux density of the specimen. The measured MFL signals were used to interpret the healthy condition of the steel cable. For improving the resolution and quantification of the damage level, digital signal processing techniques were performed. Finally, the measured MFL signals were visualized by using 3D imaging method.