Abstract: Different initial magnetization states of ferromagnetic materials have large influence on stress magnetic detection, which needs to be overcome, to improve the robustness of the magnetic measurement. Through theoretical analysis of magneto-mechanical coupling, the initial magnetization state of ferromagnetic materials can be stable and controlled by appropriately increasing the external magnetic field strength H₀. Furthermore, the rising section of the magnetization curve of ferromagnetic materials can be stably constrained within 40 MPa, which is far less than the general working load, and the falling section of the magnetization curve shows a nearly linear change with the increase of the stress. Based on this, uniaxial tensile magneto-mechanical coupling test of a Q235 low-carbon-steel specimen (with multiple cross-section mutations) was carried out, to clear the response of magnetic flux leakage signal of ferromagnetic material to tensile stress σ_t. The stress distributions of the specimen under different loads were obtained by finite element analysis, and then the effects of H₀ and tensile stress σ_t on the normal component H_p(z) of magnetic flux leakage signal were analyzed. The results indicate that by locally enhancing H₀, a relatively controllable and stable local magnetic flux loop can be formed at the examined part of the specimen, which can effectively overcome the problems caused by random and variable initial magnetization state, weak detection signal and low signal-to-noise ratio in metal magnetic memory detection. The influence coefficient φ was introduced to represent the correlative influence of σ_t on the characteristic parameter peak-peak amplitude S(z)_p-p. Within the range of 0 MPa≤σ_t≤168 MPa, the maximum increase in φ was 18.4% with the increase of σ_t.

Key words: initial magnetization state, external excitation magnetic field, magneto-mechanical coupling, finite element analysis, magnetic flux leakage testing