DEFECTOMETRY OF HIDDEN CRACKS IN METALS BY THEIR MAGNETO-OPTICAL IMAGES
DOI:
https://doi.org/10.15407/dopovidi2026.04.067Keywords:
non-destructive testing of products, magnetic field, fatigue crack, magneto-optical image, image processingAbstract
A new method for the acquisition and processing of magneto-optical images of hidden crack-like defects in metal products using a crystalline magneto-optical film is proposed. A device for capturing magneto-optical images of ferromagnetic materials based on the Faraday effect has been developed. The use of oblique illumination in the device’s design, along with an additional compensating prism placed in front of the analyzer, has made it possible to increase the inspection area, enhance sensitivity to the magnetic field scattered by defects, and ensure high contrast in the magneto-optical image of the entire inspected area. Experimental testing of this device on steel specimens with fatigue cracks demonstrated its effectiveness. To improve the reliability of defect detection, an algorithm for processing magneto-optical images was proposed; this algorithm is designed to segment and locate cracks by taking into account the characteristic features of the image. An assessment of crack width was performed based on an analysis of the normalized intensity distribution of a magneto-optical image along cross-sections of the crack. Theoretical calculations were performed to determine the distribution of the scattered magnetic field above the surface of a magnetized object at defect locations. Using a dipole model and a non-uniform distribution of magnetic charges along the edges of the defect, the profiles of the vertical component of the magnetic field scattered by the defect were calculated. The topography of the defect field as a function of its geometric parameters was obtained. The results obtained are in good agreement with experimental data. The results of the study indicate the effectiveness of the proposed device and methods for processing magneto-optical images for the non-destructive testing of steel structural elements and products.
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