Research of magnetic memory signal characteristics corresponding to early fatigue damage

A newly arisen technique named metal magnetic memory is deemed to have potentials in detecting early damage, whereas it is lack of systematic micro-mechanism research in early fatigue damage of ferromagnetic components. The microscopic fatigue experimental system including XH-500 metallograhpic microscope, DIG300 special digital camera and magnetic memory testing device, combined with the magnetic memory microscopic fatigue observation method is adopted, and the tension-tension fatigue experiment with specimens made of steel 45 are conducted. The evolution process of fatigue shortcrack initiation and growth is observed dynamically from the microscopic scale, and the variation regularity of microscopic Vickers hardness during the fatigue procedure is also given. At the same time, the variation of the magnetic memory signal on the surface of the V-shaped notch with cyclic numbers is analyzed, and the magnetic signal curve distribution regularity corresponding to different crack lengths is investigated. The results show that the magnetic memory signals exhibit an abnormal nonlinear wave when the local plastic deformation or micro-damage occurs, providing a feasible detection method for early fatigue damage of ferromagnetic materials.