Noncontact NDE technique for main cables of suspension bridges integrating direct current magnetization with a searching coil-based total flux measurement

Current inspection methods for main cables of suspension bridges are mainly carried out by visually inspecting the exterior covering of the cable periodically. In spite of necessity of non-destructive examination (NDE) to detect the inner cross-sectional damage of the main cable, a suitable NDE technique for the main cable has not been existed due to its large diameter. In this study, a crosssectional loss monitoring system that can detect the external and internal damages of main cables has been developed for the safety of long span bridges in future city This main cable NDE technique was based on the direct current (DC) magnetization technique and a searching coil-based total flux measurement. A total flux sensor head prototype was fabricated that was consisted by a magnetization part to magnetize the specimen and a sensing part to measure the total magnetic flux. The magnetic field for magnetizing the main cable was generated by applying the low frequency DC voltage to the winded coil. The sensing part was configured by two semi-circular search coils, and it measures the electromotive force that pass through the search coil by using the faraday's law of induction. Total flux was calculated by integrating the measured magnetic flux. Then, B-H curve was extracted using the total flux, and cross-sectional loss can be detected using variation of features from the B-H curve.