Detecting surface-breaking flaws with a Hall effect gradiometric sensor

Abstract

Magnetic scanning devices for structures, components, and materials have been the subject of intense scientific research and are potential prototypes for use in industry, especially in non-destructive inspection, to identify defects in metal structures subject to extreme conditions such as high temperatures, pressure, and strong tension. These conditions can lead to the failure of these structures, affecting their operation and resulting in losses and possible accidents. In this sense, we built a device for scanning magnetic response in defective steel plates. The device is composed of two Hall effect sensors (Melexis MLX 90215) in a gradiometric configuration. Using this device, it was possible to identify defects produced by electric discharge machining in SAE 1020 steel plates and proved to be efficient in detecting defects with diameters and depths of the order of 0.90 mm and 100 µm, respectively. A filter system on a printed circuit board was also developed to attenuate noise. The signal-to-noise analysis showed the circuit was effective, leading to identification of defects. To reinforce the application of this equipment in scientific research and industry, we developed a theoretical model to estimate the depth of defects.