Magnetic Nanofluid Based Approach for Imaging Defects

Abstract

Magnetic flux leakage is one of the most widely used electromagnetic nondestructive techniques to locate and assess discontinuities such as fatigue, cracks, corrosion, erosion, non metallic inclusion and abrasive wear in magnetic components. Here, we report a new optical technique for imaging internal defects in materials using a magnetically polarizable nanofluid (ferrofluid). The gradient in the magnetic flux lines around the defective region induces the formation of one-dimensional array of nanoparticles along the field direction in the nanofluid, which produces a discernible gray level contrast in the ferrofluid. The grey level contrast produced by the leaked magnetic flux is exploited to detect defects buried inside the sample. The normal and tangential components of leakage magnetic fluxes have been modeled using a dipole approach for rectangular and cylindrical defects of different dimensions. The simulated results are validated experimentally. Various image processing techniques such as contrast stretching, image gradient, contrast limited adaptive histogram equalization and image profiling are used to obtain better detection sensitivity.