Stress concentration degree affects spontaneous magnetic signals of ferromagnetic steel under dynamic tension load

Under the excitation of geomagnetic field, stress can induce spontaneous magnetic signals in ferromagnetic materials, which can be potentially applied to estimate the damage degree. In this research, the normal component of magnetic field, H_p(y), was measured during dynamic tension test on the surfaces of ferromagnetic specimens having different stress concentration factors, α constant amplitude sinusoidal tensile load cycles were applied on 18CrNi4A steel plate specimens whose α were respectively 1, 3 and 5. Then correlation of H_p(y) values’ changes with loading cycles reported. The results indicate that stress concentration factor, α extremely affects the magnetic signal, the absolute value of the gradient, |K|, increases with the increase of α. Meanwhile, |K| also goes up when loading cycle increases in the initial state. However, after a few cycles, those H_p(y) curves corresponding to different cycles become similar before cracking.