We investigate the influence of magnetic domain configurations on the magnetic Barkhausen noise (MBN) and magneto-mechanical behavior of electrical steel. Micro-macro magnetic properties from individual crystallographic grains with different domain wall (DW) orientations under different tensile stresses are measured. We show a strong dependency of the MBN activity and magneto-mechanical behavior on the DW orientation. Time evolution and statics of magnetic domain states are elaborated for the analysis of the magnetization processes, revealing an interaction between the stress-induced demagnetizing effect, the magneto-elastic behavior and the DW dynamics. The variation of supplementary domains under tensile stress is directly connected to the demagnetizing effect, further affecting the MBN activity. In addition, the influence of magnetic domain configurations in the neighboring grains on the DW dynamics and MBN jumps is studied. From this, the dipolar-dipolar and intergranular magnetic coupling interactions are derived. The results provide substantial microscopic insight for MBN and magneto-mechanical behavior analysis.

Nondestructive inspection of rolling contact and stress corrosion cracks is a critical important research area in both science and technology industry to evaluate the properties of a product. This paper proposes a novel system of circle-ferrite pulsed inductive thermography for cracks inspection. The new sensing structure consists of several promising characteristics. It significantly enhances the detectability of omnidirectional micro cracks, and provides larger detection area with non-geometry influence. In addition, unlike common inductor, the proposed structure imposes uniform toroidal electromagnetic thermal fields, so that both sensitivities of detection rate and the detectable area can be simultaneously improved. This overcomes the problem of in-homogenous heating, and increases the thermal contrast between directional defective and non-defective region. The theoretical derivation based on magnetic circuit principles has been developed for analysis and interpretation of the results. In addition, both simulation experiments and tests on artificial and nature cracks sample have been conducted to show the reliability and efficiency of the proposed system.

In order to solve the difficulty in localization and poor signal-to-noise ratio (SNR) of the angled shear vertical wave (SV wave) electromagnetic acoustic transducer (EMAT) in cracks detection of high-temperature carbon steel forgings, a finite element (FE) model of the angled SV wave EMAT detection process was established, and the influence of specimen temperature on the EMAT excitation, propagation, and reception processes was analyzed. A high-temperature resistant angled SV wave EMAT was designed to detect carbon steel from 20 °C to 500 °C, and the influence law of the angled SV wave at different temperatures was analyzed. Then a circuit-field coupled FE model of angled SV wave EMAT in the carbon steel detection process based on the Barker code pulse compression technique was established, and the effects of the Barker code element length, impedance matching method, and matching component parameters on the pulse compression effect were analyzed. In addition, the noise suppression effect and the SNR of the crack-reflected wave in the tone-burst excitation method and the Barker code pulse compression technique were compared. The results show that the amplitude of the block-corner reflected wave decreases from 556 mV to 195 mV, and the SNR decreases from 34.9 dB to 23.5 dB when the specimen temperature increases from 20 °C to 500 °C. When the temperature is 500 °C, the SNR of the crack-reflected wave obtained by the Barker code pulse compression technique can be improved by 9.2 dB compared to the tone-burst excitation method with 16 synchronous averages. The study can provide technical and theoretical guidance for online crack detection for high-temperature carbon steel forgings.

There is a need in industry to supply safe, effective and reliable technique to characterize the stress of steel components and structures, both at the manufacturing stage and in service. Bridging the correlation between micro and macro magnetic properties and the applied tensile stress is the first conceptual step to come up with a new method of non-destructive material testing. We investigate the stress-associated changes in domain wall dynamics in grain-oriented electrical steel by in-situ magnetic imaging using magneto-optical indicator films. The 180° domain walls velocity distribution is used as a parameter for applied stress determination. Additionally, the in-plane magnetic stray field above the surface of the sample is synchronously measured for stress evaluation. The variations in magnetic stray field outside the sample under different loading are investigated for the analysis of the domain wall dynamics. From this, an interrelation of the domain wall dynamics and magnetic stray fields with varied tensile stress is derived. The results provide substantial microscopic and macroscopic insight for the interplay of domain wall dynamics and stress-induced demagnetizing effect.