Multigradient Characterization of the Strain in Low-Carbon Steel Components Based on Magnetic Barkhausen Noise Method

Based on the hypothesis that each magnetic domain is considered as a magnetic Barkhausen noise (MBN) emission “source,” a layered model describing the generation mechanism and propagation attenuation of the “source” signal is built. The mathematical description of the MBN derived from the excited ferromagnetic materials is given. According to this, a novel multigradient nondestructive characterization and testing method is proposed; and a concept “MBN multigradient nondestructive testing and evaluation (NDT and E)” is introduced innovatively. The proposed model lays the theoretical basis for “MBN multigradient NDT and E,” and links the division of MBN frequency bands with different testing gradients. Then, using a specimen made of Q235 steel, the classic four-point bending experiment was implemented. The MBN eigenvalues of time-domain voltage, of spectrum density, and of power spectral density were extracted under different loadings. The final results showed a turning point under some specific testing gradients; this indicates the material has initial yielded. Comprehensive analysis of all results, which perfectly reveal the inhomogeneous layering stress/strain levels, elastic/plastic deformation of the specimen distributed along the depth direction. The proposed “MBN multigradient NDT and E” method can more completely and fully characterize the mechanical properties of the specimen quantitatively or semi quantitatively; and has important theoretical and practical significance.