Research On The Magnetic Memory Testing Method Of Ferromagnetic Component

With rapid development of our country,the use of ferromagnetic material is also increasing rapidly.At the same time,it brings more dangers.Fatigue corrosion and other factors can form metal damage and failure,then may cause serious accidents.Therefore,it is important to detect ferromagnetic materials defect.Metal magnetic memory(MMM)testing technique is a novel nondestructive technology.Compared with the traditional NDT methods,it has a unique advantage.Not only can MMM detect microscopic damage,but also can test macro defect.Besides,the testing specimens do not need any pretreatment.The raise of the technique was accompanied by attentions.Many scholars have carried on the related research both at home and abroad,which have lots of results but still require more efforts.Firstly,in this paper,from the point of energy and self-magnetic leakage field(SMLF),the mechanism of metal magnetic memory signals is described by introducing the characteristics of ferromagnetic materials.In order to explore the influence factors of MMM signals,magnetic dipole model is established.Then the change of the MMM signals is analyzed using this model while parameters like lift-off value depth and width of the defect are changing.Then,a phenomenon is found out by experiment using MMM testing technique.Because the magnetic signals and gradient features of non-defect are similar to those of defect,it is easy to cause misjudgments and omissions.In order to distinguish these two signals,the influence of lift-off value is analyzed by experiment and model simulation.Based on the different performance,a multiple lift-off value method is introduced to accurate positioning defect and is proved by the experiment results.Finally,a testing instrument is made according to MMM testing technique.After determine the testing purpose,the instrument is divided into four systems.Then the specific implementation is designed based on the function of each system.After debugging and testing,contrast experiment are carried on by using this instrument and another testing equipment.Results show that the instrument can effectively obtain magnetic field information of material surface.And it can correctly reflect changes of the magnetic field and gradient value caused by the defect,proving that it can locate position of the defect.