The Research Of Mechanism And Application Of The Metal Magnetic Memory Testing

The Metal Magnetic Memory Testing (MMMT) is a technique of magnetic flux leakage testing. Different from other magnetic-based testing techniques, externally applied magnetic field is not required in MMMT. The whole testing can be carried out just in the geomagnetic field. When the magnetic field line passes through the defects or stress concentration zone, there will be a magnetic leakage field on the surface. By means of high-precision magnetic detector, MMMT equipment can find out the features of the defects or the stress concentration zone.A review of the researches of MMMT in aspects of mechanism, equipment and application was made in this dissertation. Then, the magnetic physics and mechanics of materials which serve to be the basis of MMMT were studied. Also, the specific MMMT system which was developed by our team later was introduced.First of all, the tensile test samples with various kinds of notches were manufactured. Then, based on ANSYS, stress condition of some simulation models was analyzed before carrying out the tensile test. Moreover, the effects of MMMT signals of samples with different notches, scanning route and geomagnetic field direction were thoroughly analyzed. At last, the character and regularities of the MMMT among three kinds of steals such as Q235#,45# and 40Cr# were found out.Consequently, MMMT was applied to the engineering field. The application of the MMMT in wheels, bridge and bolster guide of the railbound vehicles was analyzed, then the MMMT in the welding seam was applied. By contrast of the result of the magnetic particle testing, radiographic testing and destructive testing, the application of the MMMT was confirmed to be suitable.