The magnetic leakage field of surface-breaking cracks

A 2D mathematical model for the magnetic leakage field of surface-breaking cracks in ferromagnetic materials is developed. The expressions are shown to be valid for 3D defects provided they are at least twenty times as long as they are deep. The model is tested by comparison with measured leakage fields for the range of artificial cracks. The magnetic forces experienced by a small magnetic particle in a leakage field are also calculated and the level of magnetic field strength required for magnetic particle crack inspection is discussed.