Research In Magnetic Damage Detection Technology Of Homogeneous Ferromagnetic Materials

Ferromagnetic materials(FM)are widely used in many fields,such as construction,bridges,railways,petroleum,subways,etc.In recent years,due to the numerous collapse accidents of steel structure people focus more on their safety more and more attention.In order to prevent and avoid the occurrence of safety accidents,it is of great theoretical significance and research value to find out the damage position and degree of FM in time and accurately.The main contents are outlined as follows:(1)The study of two-dimensional online magnetic field strength detection system.Most of the existing metal magnetic memory(MMM)detection systems can only realize one-way detection,and the data cannot be stored in real time.Therefore,this paper designs a two-dimensional on-line magnetic field strength detection system,which can detect magnetic of Tangential and normal the same time.Using cutting machine make different damage degree of crack and circle in a homogeneous FM surface,then study the change of magnetic field under external loading with experimental comparison method.Second using numerical normalization method to normalize the magnetic field data,and display it in 3d coordinate system.The damage location and damage type are identified according to the size of the extremum and the range of its occurrence.(2)Damage characteristics analysis study.We cannot directly determine the damage degree of FM according to the numerical value of magnetic field.By analyzing the basic theory of wavelet transform and wavelet packet transform,this paper uses wavelet packet energy spectrum analysis method to process the tangential magnetic field of homogeneous FM.First,and we can achieve a 32 dimensional energy percent feature vector.Finally,Using the principal parameter analysis and threshold to reduce the dimension of feature vector,get the 8-D energy spectral feature vector.Using the BP neural network to train the eigenvector to predict the damage degree of different damage types,the results show that the method of wavelet packet Energy spectrum analysis is good for judging the damage degree of FM.(3)Damage mapping study.In order to determine the damage location of FM,this paper proposes a method of color mapping.It maps tangential magnetic field of FM to RGB color phase space.Then use gray-scale and binary image to deal with the map,the damage type and location were determined according to the area of color mutation.The results show that the method of color mapping can directly detect the damage type and location according to the area and shape of the damaged area,but the recognition effect of deep damage is not satisfactory.This paper adopts time domain,frequency domain and image to study the change of magnetic field of homogeneous FM in different damage types and different degree.The experiment result shows that time domain is able to quickly find the damage of FM.And frequency domain is capable of finding the damage degree of FM.Image can find damage location and type of FM.Therefore,it can more quickly and accurately identify the damage location and damage degree of ferromagnetic materials with the three methods.