RESUMEN
Magnetic hysteresis properties are sensitive to stress in ferromagnetic materials. This suggests that magnetic measurements are a potential method to evaluate residual stress in steel products. Nevertheless, nondestructive inspection of residual stress by using magnetic properties has been limited, because bulk properties over the entire sample are usually obtained in conventional hysteresis curve measurements through electromagnetic induction, thus, local hysteresis properties are not measured. However, the spatial mapping of local hysteresis properties has been demonstrated recently by ultrasound focusing and scanning. This technique is based on the generation and detection of the acoustically stimulated electromagnetic (ASEM) response. In this study, we investigate the stress dependence of local hysteresis loops through the ASEM response using a tensile testing machine and provide conversion coefficients to estimate tensile stress from the values of local hysteresis properties. The results indicate that the hysteresis properties associated with coercivity, remanent magnetization, and hysteresis loss are promising parameters as an index for evaluating residual stress.
RESUMEN
We present ultrasonic techniques for magnetic measurements. Acoustically modulated magnetization is investigated with sensitive rf detection by narrowband loop antennas. Magnetization on the surface of ferromagnetic metals is temporally modulated with the rf frequency of the irradiated ultrasonic waves, and the near-field components emitted from the focal point of the ultrasonic beam are detected. Based on the principle of the acoustically stimulated electromagnetic (ASEM) response, magnetic sensing and tomography are demonstrated by ultrasonic scanning. We show that ASEM imaging combines good acoustic resolution with magnetic contrast. The sensitivity of this method is estimated to be about 6 G/Hz(1∕2) in our current setup.