Electromagnetic testing emt-mft chapter 9b

2.0 Principles of Magnetic Leakage Field Testing MLFT
2.1 Origin of Defect Leakage Fields.
The origin of the flaw leakage field is illustrated in Fig. 1. Figure 1(a) shows a
uniformly magnetized rod, which consists of a large number of elementary
magnets aligned with the direction of magnetization. Inside the material, each
magnetic pole is exactly compensated by the presence of an adjacent pole of
opposite polarity, and the net result is that interior poles do not contribute to
the magnetic field outside the material. At the surfaces, however, magnetic
poles are uncompensated and therefore produce a magnetic field in the
region surrounding the specimen. This is illustrated in Fig. 1(a) by flux lines
connecting uncompensated elementary poles.
Charlie Chong/ Fion Zhang