Fold Mark Characterization Using a Magnetostrictive Probe

摘要

The JSC340P steel is a primary material for a vehicle roof panel. It’s subject to alternating line defects of bright & dark across the rolling direction. The alternating lines can be found with grinding the strip surface but difficult to be recognized and quantified. A proprietary magnetic stress sensor was applied to measure the stress variation of the steel strip surface. The principle of the sensor used was the magnetostrictive method and the magnetic anisotropy method. A sample of steel strip was measured along the rolling direction and a stress undulation curve was obtained. FFT (fast fourier transform) of the curve exhibited a strong magnitude at the wavelength of 15-20mm, which coincided with the pitch of the defect by visual inspection, and the alternate lines were measure. The peaks and troughs of the curve are corresponding to the bright and dark lines on the sample surface. With multiple repetitive experiments, the sensor was validated to be capable of characterizing the defect.