Research On Quantitative Evaluation Of Two Dimension Of Magnetic Memory Testing

For sensitive of stress concentration zone, Metal Magnetic Memory (MMM) testing technology which can diagnose the component damage early and prevent the happening of the disaster has widely been focused on by researchers at home and abroad in recent20years. Some results were found in the aspect of testing mechanism, experiment research and engineering application, while there was no breakthrough in quantitative evaluation of stress concentration. Based on the mechanism of magnetic memory effect, combined with finite analysis method to simulate stress-magnetic coupled effect, the paper attempted to provide experiment criterion of quantitative evaluation of MMM testing so that it can serve well in the modern industrial detection by means of static loaded tension and low fracture experiment.On the basis of two Dimensional (2D) detection of MMM, the synthesized Lissajous after differential was analyzed, algorithm was proposed and the best one was used to solving the equivalent area of the closed filed of Lissajous, meanwhile the evaluation method about closed or unclosed filed was pointed out. The distribution of the equivalent stress on specimen surface was simulated under tensile and fracture stress, and the reliability of2D testing of MMM was tested and verified through the distribution curve of leakage magnetic field on different stress which was obtained by static magnetic analysis.The steel of20#and45#was utilized to do tensile experiment. Two measurement method, Offline and online, was adopted to detect he magnetic signal, also the surface tangential component, the normal component and the characteristics of the synthesized magnetic memory2D curve similar to Lissajous was compared and analyzed in the two methods. At the same time, different notched specimens were designed and the magnetic signals from different specimen surface were measured and handled. The results showed that:Different measurement methods had the same variation results, which is as the stress increased the magnetic signal increased first then decreased finally increased, while as for the online measurement the result is affected by the fixed load; Towards the notched specimens, the significant characteristic phenomenon of magnetic memory signals appeared around the notches, and the changes of the signals on both sides of the notch was Asymmetry; The correlation between tangential component signal and stress is better than that of normal component; The bigness of the enclosed filed of Lissajous changes nonlinear with the stress increases, and the nonlinear fitting curve was considered to quantitative evaluate the state of the stress concentration zone.The30CrMnSiNi2A steel was applied in low fatigue experiment, different thickness specimen’s surface magnetic signal was detected under different cycles, the relationship between magnetic signal and fatigue cycles was researched, and the Lissajous analysis was introduced to discuss its enclosed field’s equivalent area’s changes with different fatigue damage. The results showed that:Once the fatigue stress was executed, the magnetic mutation of magnetic signals of specimen surface will happened, which could be used to indicated the condition of stress concentration, and their differential value could be used to find the concentration zone; As the cycles increased, the variation of the normal component and the tangential component was different; In the whole fatigue process, the equivalent area of the enclosed field of Lissajous followed Logistic curve changes, it can be divided into4stages:first increased, then tend to stable, next reverse reduced, finally surged after recovery; Towards different thickness specimens, specimen thicker the fatigue life lower and brittle fracture more easily, however, the variation of magnetic signal was almost the same in the fatigue process.Finally, some suggestion was put forward in the aspect of mechanism research, quantitative evaluation, detection standard to promote the development of MMM testing technology, and improve its application in engineering practice.