Magnetic field patterns as a tool for stress estimation in steel samples

In this work, steel square samples were subjected to varying degrees of compression, resulting in a distribution of simultaneous compressive and tensile stresses within the samples. The tangential component of the surface magnetic flux density was mapped along both the direction of compression and perpendicular to it, using a magnetic sensor, for each level of compression. The results show that the maps of the relative difference of magnetic flux density for different levels of applied stress, with respect to the flux density at zero stress, exhibited a diagonal stripes pattern. This pattern was discovered thanks to the particular surface stress distribution in square samples. The formation of these patterns could be attributed to the re-orientation of magnetic domains due to stress and the magneto-elastic effect, which was confirmed by the change in orientation of the magnetic flux density vectors obtained from the measurement of two of their components. Additionally, the maps showed an increase in contrast between high and low values with an increase in applied stress. Finally, the maps of the module of the gradient of magnetic flux density displayed a distinct diagonal chessboard-like pattern, and the contrast between low and high values increased with an increase in applied stress.