Mechanism And Experimental Study Of Magnetic Memory Effect Under Fatigue Load

Due to the structural fatigue factors in the world every year,a large number of products fail in the design life period,and the major accidents caused by fatigue damage also occur frequently.Metal magnetic memory is a form of stress-magnetic effect,which has advantages over the early detection of stress concentration and fatigue damage.However,the study of magnetic memory mechanism and early damage identification method is not deep enough to provide a more reasonable explanation for experimental phenomena.In this paper,the mechanism of magnetic memory under cycle stress and its damage detection method are discussed based on theoretical analysis,experimental study and numerical simulation.The fatigue test load is designed in advance based on the fatigue life analysis software.The static analysis of the model was established in Workbench to obtain the stress distribution state and the weak parts of the specimen,while the fatigue life analysis was carried out in n Code Design Life.It is found that the maximum load change has less influence on the fatigue life of the specimen than the stress ratio.The changing process of the magnetic memory signal in key parts of the specimen under different cycles is monitored on-line based on the fatigue test,and the experimental results show that the change of the magnetic memory signal in the whole fatigue life can be divided into three stages,which coincides with the three stages of fatigue.This phenomenon is explained based on the dislocation theory,meanwhile,early fatigue damage identification method is proposed.The micro-mechanism of magnetic memory effect under fatigue loading was studied by powder pattern method.The macroscopic magnetic signal data were obtained based on the off-line detection method under cyclic stress,and the multi-scale fuzzy entropy feature index was extracted.Moreover,the in-situ magnetic domain observation of Q235 B steel under different fatigue cycles was realized by the powder pattern method.It is found that the magnetic domain morphology changes continuously after the cyclic stress,and turns to the direction of stress and has a consistent trend of orientation.