The incremental permeability (IP) is related to the reversible domain-wall motion of ferromagnetic materials during the period of dynamic magnetization. IP feature γ can be used to estimate the yield strength of materials. However, the IP signal generated by reversible domain-wall motion is weak. During the experiment, the vibration of the platform and the uneven surface of the sample will change the lift-off conditions of the probe, resulting in the distortion of the IP signal. In order to solve this problem, in this paper, a two-parameter fitting method is proposed to optimize the estimation of yield strength by γ. Two compensation parameters a_γ and b_γ related to lift-off are proposed to modify the γ curve, making it possible to detect the material under different lift-off conditions. Finally, the yield strength of the material is estimated under different lift-off conditions, and the estimation error is less than 10

Typical Incremental permeability (IP) requires a high power supply to generate a bias magnetic field that periodically magnetizes the testing samples, making it difficult to apply to occasions where high power supply is short. To solve this problem, this paper presents a low power NDT method based on IP, which is characterized in that the permanent magnets are used to form a bias magnetic field, and the sample is magnetized aperiodically by moving the permanent magnet in one direction. Finite element simulation is used to compare the magnetic fields formed by permanent magnets with different number of blocks and distance between them, as well as the hysteresis curves under magnetic excitation, and a finite element simulation method (FEM) of IP is given. Our experiments used the new method to estimate the yield strength of steels, demonstrating that the proposed method can obtain an approximately accurate result, and its power consumption is less than 2 W.

In the current production of iron and steel industry, the testing of mechanical properties of ferromagnetic materials relies on tensile testing, which is time-consuming and destructive, thus greatly increasing the production cost. In order to solve this problem, a method based on pulsed eddy current is proposed to estimate the yield strength of ferromagnetic materials. Eddy current loss and hysteresis loss are the sources of loss in the magnetization process of ferromagnetic materials. Not only the loss but also the yield strength of the material is related to the microstructure of the magnetized material. In this paper, the relationship between loss in the process of magnetization and microstructure of materials is analyzed. The features of eddy current loss and hysteresis loss were found from the pulsed eddy current signals, and the yield strength evaluation model was established by feature fitting. The experimental results show that the model has high evaluation accuracy.