Finite element modeling of electromagnetic NDT phenomena

The development of computer-based defect characterization schemes for automated electromagnetic methods of nondestructive testing (NDT) requires adequate mathematical models to describe the complicated interactions of currents, fields and defects in materials. This paper describes the finite element equations governing active, residual and eddy current phenomena in materials with discontinuities and magnetic nonlinearity. It is suggested that the resulting magnetic vector potential values can then be used to calculate measurable electromagnetic quantities, such as magnetic flux density in the vicinity of defects in active and leakage field NDT methods and the complex impedance of a sensor placed near a defect for eddy current NDT techniques. The power of this numerical technique is demonstrated by comparing predicted results with experimental values for practical examples of active, residual and eddy current NDT situations.