Metal Magnetic Memory Representation Of Cumulative Fatigue Damage

In the field of aerospace, petrochemical, and other important industrial, the main failureof machinery and its components is fatigue damage under fatigue load for a long time. Suddenfracture without signs leads to stop running, which causes huge economic losses. Weldedjoints as the main connected structure, often exist the defects of uneven in metallographicstructure, at the location which fatigue fracture often takes place. Thus, research oncumulative damage of weld components under the fatigue loading is necessary.Traditional NDT methods are difficult to test early defects such as micro cracks andstress concentration. These defects not only increased the chance of fatigue failure onvibration components, also reduces effect of the equipment preventive maintenance. MetalMagnetic Memory (MMM) testing is developed in the late last century and introduced intoChina, which can detect the micro defects and stress concentration on ferromagneticcomponents based on the magnetic mechanical effect.The paper aims at introducing the magnetic memory testing into the field of fatiguecumulative damage representation of vibration component. Used the advantages of MMMtesting in early diagnosis and combined with the fatigue cumulative damage experiments,mechanism of magnetic memory effect and representation of fatigue cumulative damageunder the fatigue load.First, vibration components with welded joints are conducted by the fatigue damageexperiments. The magnetic memory signal and correlation rule are obtained under multi-stageloading level, which verifies the increasing of the residual magnetic induction intensity withthe increasing of the fatigue load. In order to further explore the relationship between fatiguecumulative damage degree and the magnetic memory signal, the magnetic memory N typedescription model has been established. Finally, residual stress of welded joints is simulatedby the finite element analysis software ANSYS. And ANSYS-Fatigue module is used to solvethe fatigue life of welded specimen under the working load. The good consistency of thestress nephogram under the experimental load and the MMM equipotential graph, verifies theeffective and scientific of MMM testing for vibration component fatigue cumulative damage.