Analysis of Leakage Magnetic Field of Rectangular Shaped Defects in Magnetic Materials and Investigation of Magnetic Fluids in the Field

Magnetic Particle Inspection (MPI) is a non-destructive testing (NDT) technique widely used in industry to detect surface and sub-surface flaws in ferromagnetic materials. MPI is a simple, fast, and cost-effective technique, particularly useful for evaluating the integrity of welds and critical parts. Detecting surface and sub-surface defects in ferromagnetic materials is essential for ensuring product quality, safety, performance, and regulatory compliance across various industries. Therefore, in this study, the magnetic field and its gradient for rectangular prism-shaped defects in ferromagnetic materials were analyzed. The magnetic fields were calculated using analytical equations. The magnetic field of a 2x7x19 mm sized permanent magnet was measured using a gaussmeter to verify theoretical results. Subsequently, these analyses were used to interpret the forces acting on non-interacting micro to nano-sized particles and magnetic fluid on the crack region. The EFH-1 light hydrocarbon-based magnetic fluid, with an average particle size of about 11.6 nm, was used to experimentally study a 1x1.5x62.5 mm crack on a solid magnetic material. The distribution of the magnetic fluid on the crack was studied for different heights and magnetic field values. For a 2 ml layer of EFH-1 at a height of 2-3.5 mm from the magnetized material, a nearly Gaussian-shaped fluid distribution with a width of around 3.7-5.0 mm was observed. The experimental results are presented and compared with the theoretical analysis.