Experiment Research Of Metal Magnetic Memory Technology In Weld Residual Stress Testing

As an important industrial tesing mean, nondestructive testing plays an important role in guaranting equipments safety and keeping the process of industrial production smooth. Metal-magnetic-memory technology is one kind of new nondestructive testing methods. For the advantage of early diagnosis to the equipments and components, in recent years magnetic-memory technique attracts widespread attention. So once the metal-magnetic-memory technique is applied to testing weld residual stress, it not only can detect the residual stress concentration areas, but also cause nondestruction to the components.This paper firstly has been simulated general welding process with ANSYS, and gives the size and distribution forms of residual stress. Furthermore, the simulated results provide the reference for the experiment plan formulation of metal magnetic memory testing residual stress that in the specimens.Then the flat plate specimen is tested with the metal-magnetic-memory method from vertical direction and parallel direction of the weld,the normal component of leakage magnetic field Hp(y) and the gradient value K was captured. By comparing the curves’ shape of normal component of leakage magnetic field Hp(y) on the different vertical direction detection paths and investigating the change of Hp(y) on the detection path in the vicinity of the weld and heat affected zone and analyzing the numerical variation of the normal component Hp(y) of the leakage magnetic field in the weld, this paper proposes the stress amplitude ΔH to evaluate the size of the residual stress. The feasibility of defining ΔH as a criterion has been proved by comparing the data with throse got from the parallel direction.After that the blind-hole method is carried out to caculate the residual stress in where been evaluated existing,testing results accord with the original judgment.Besides, the equivalent of magnetic-memory method are compared with that of blind-hole method. Finally, T joint Angle weld is tested by the magnetic memory technique, and the residual stress intensity factor KNH is used to evaluate the size of the residual stress.Finally, this paper uses the wavelet analysis to process the magnetic memory signals.Firstly the wavelet de-noising method is studied.By comparing the effects of the differentwavelet de-noising functions, this paper obtains the best wavelet de-noising method.Then the magnetic signals are discreted and reconstructed by one dimensional wavelet, and the characteristics of residual stress is extracted. It proves that wavelet selective reconstruction can process the magnetic memory signals.