| Pulsed magnetic flux leakage testing is a new emerging nondestructive testing technique, and hasa great potential in ferromagnetic materials examination. It well inherits the advantages of traditionalmagnetic flux leakage testing such as low cost, high sensitivity, no need of coupling agent and highspeed on-line testing. Furthermore, it can detect defects at various depth, due to the broadband pulseexcitation with its rich frequency information.This paper is organized as follows: the principle and related theory of pulsed magnetic fluxleakage testing are illustrated, based on which a2-D FEM simulation is build. The simulationanalyzes the distribution of magnetic flux leakage near different kinds of groove-shaped defects. Anexperimental setup for pulsed magnetic flux leakage testing is built in ferromagnetic materialsexamination, including a probe, a pulse excitation generator, a signal-processing circuit, and a DAQdevice. A2×8array hall sensors are used to respectively measure the horizontal and verticalmagnetic flux leakage components, achieving large-area and high-speed detection. A software systemis built with VC including signal preprocessing, feature extraction, and testing procedures. Theacquired signals are filtered via wavelet method, and feature points of the differential signal areextracted both from time domain and frequency domain.The designed testing system is used to research two series of groove-shaped defects, one of thesame width and various depth, the other of the same depth and various width. The influence of pulseexcitation parameters on the magnetic flux leakage is analyzed. The size of the defect is determinedaccording to the horizontal and vertical magnetic flux leakage components. The surface andsubsurface defects are distinguished by the changing rate of the differential signals. To be brief, thedefects are located and characterized according to the extracted feature points and a dynamic scan isachieved based on the static defect detection. |
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