Magnetic Memory Testing Principle And Its Application Technology

As the development of the science and technology, the quality of products become more and more important. The focus of the inspection goes from the macroscopic imperfection to its source prediction. After the diligent study of the scholars from abroad, as a new detective technology, the Metal Magnetic Memory Testing (MMMT) was found in the 1990s of 20th century. Compared to the normal detective technologies, the MMMT has many advantages such as high-speed, non-externally applied magnetic field and low cost. However, because of the short development history, not only equipment but also the practical application of the MMMT need to be further studied. In the background of the project titled"The application research of the MMMT on the important components of the railway vehicle(2004 NCK0 57)"supported by China South Locomotive and Rolling Stock Industry (group) Corporation, the mechanism, equipment and application of MMMT are studied in this dissertation. The data processing system(DPS) is also developed. Then, the technology support for the practical application was provided.The cooperative action of the magnetostriction and the magneto-mechanical effect makes the mechanism of the MMMT. The geomagnelic effect, magnetostriction and the magneto-mechanical effect on ferromagnetism items were analysed based on the theory of ferromagnetism. The reason why the MMMT can find the defects and stress concentration zone was explained. The investigation shows that the MMMT is the only effective method which can give the early diagnosis of the ferromagnetism items.The components of the MMMT equipment were designed based on the basis of the mechanism. It makes smoothly for the operators to analyze the results by measuring the Hp(y) and its gradient change |Kσ_Z|. In addition, the hardware circuit, system software and the detector are studied and designed. Specially, the the magnetic sensor which considered to be the most important component of the MMMT detector is analyzed thoroughly and studied. After the research and design of the all parts, the MMMT equipment was manufactured.The data processing software system which based on the Microsoft Windows of the MMMT was developed. The DPS have many advantages such as high-speed, easy to use and powerful function. The system can not only keep track of the date but also analyze it by the present data processing method such as Excel. It also can give many displays in vary kinds chart and carry some mathematics calculation and analysis. All in all, the DPS provides a scientific tool for the MMMT and have a important value for the practical application.The experiment and the analysis of the MMMT with differernt component were carried out. The result shows that the |Kσ_Z| on the defects and stress concentration zone were unique. The new method using gradient change of magnetic leakage field |Kσ_Z| as criterion is used to determine the defects and stress concentration zone in this dissertation.Some useful conclusions were sumed up after analyzing the effects of MMMT signals of samples with different notches, scanning route, geomagnetic field direction and the different steels. Thorough the analysis, the regular change of the |Kσ_Z| was found follow the change of the stress concentration zone. The maximum of the |Kσ_Z| appeared on the most stress concentration zone. The plastic and pliable materials were consideed to have the less |Kσ_Z|. Over and above, both the normal component of the magnetic leakage field (Hp(y)max) and the |Kσ_Z| became smaller in contrast to the increase of the F in axial direction.The relation between the magnetic particle testing, X-ray testing, destruction testing and MMMT was found out through the application research on wheels, bridge, bolster guide of the railbound vehicles and the welding seam. The results showed that the accuracy of the MMMT was better than the normal magnetic particle testing in the testing of the radials holes and the coupling gears when the |Kσ_Z| surpassed 50 and 100 respectively. The accuracy and credibility of the MMMT was also better than the X-ray testing in the testing of welding seam when the |Kσ_Z| surpassed 50. In short, the application of the MMMT was confirmed to be suitable in the engineering field.