Application Of Wavelet Anailsis In Magnetic Memory Testing

This text studies Metal Magnetic Memory Testing (MMMT for short) from the twosides of mechanism and use. The three kinds of steel (X80, Q345R and Q245R), which arecommonly used in the petrochemical industry, are stretched in the tensile test machinebased on the principle of ferromagnetic materials’magnetic memory. The MMM signalsof steel are measured at different loads; In order to study the affect which is caused by thestress concentration and its location, some of the specimens are processed withprefabricated defects. The locations of defects on the specimens have two situations: oneis that the defects are in the center of the specimens; the other is the defects deviated fromthe center of the specimens. Wavelet analysis is introduced into the signal processing ofMMM to get accurate results in this article.The results of the test show that the location of zero point depended on the relativeposition of defect in the specimen. Starting from the basic principle of magnetic memory,the text analyzes the reason that the location of zero point drift with load changing byequivalent model with a magnetic dipole. The result shows that it does not apply in allcases that the use of zero point as the standard of MMM, which have great limitations.To be able to use wavelet analysis effectively in MMM testing signal processing, thistext presents selective reconstruction of wavelet analysis. This method not only canremove the noise signal from the detected signal, but also can extract characteristic signalin the location of stress concentration from original signal. The center of the characteristicsignal consists with the location of stress concentration, and is in line with the equivalentmodel with a magnetic dipole analysis conclusion. The test result of pressure vessel weldsby magnetic memory and ultrasonic verifies the accuracy of this method. This method isalso useful for the study of the microscopic mechanism of MMM.These results provide some guidance for promotion and practical application ofMMM technology...