Influence of tensile stress on magnetic flux leakage signal of ferromagnetic steel after overcoming initial magnetization disturbance

By locally enhancing the intensity of external excitation magnetic field (H0), a relatively stable local flux loop is formed at the test site, which can effectively overcome the problems of random and variable initial magnetization state, small test data base and low signal-to-noise ratio of ferromagnetic specimens in metal magnetic memory testing (MMMT). The results of magneto-mechanical coupling theory and experiment study show that under tensile stress (σt), the ascending part of the magnetization curve is stably constrained within 40 MPa, which is far less than the normal working load, and the descending part of the magnetization curve changes almost linear with the increase of σt. The gradient value of normal component (dHp(z5)/dx) increases by about 105% and the relative gradient value (Δ[dHp(z5)/dx]) increases by about 76% in the range of 0 MPa ≤ σt ≤ 180 MPa with the increase of σt. When H0 reaches 943.4 A/m and 1415.1 A/m, the characteristic parameter namely peak-to-peak amplitude, S(z)p-p, can stably describe σt linearly.