Eddy Current Testing
Principle of the method
The non-destructive control process with Eddy-currents highlights the changes in the physical properties of a controlled object using an alternative or moving magnetic field. Basically, the controlled piece is brought into the interaction zone with an alternate magnetic field produced by a coil. The field of the control coil induces in the piece Eddy currents which produce an alternative magnetic field opposite to the field of the coil. Modifications of the magnetic field generated by these currents due to inhomogeneities or discontinuities of the controlled material taken over by the appropriate equipment allow the defects in the controlled material to be highlighted. The testin process depends on the measurement arrangement, frequency, electrical and magnetic properties, as well as the dimensions of the part.
The method is used for a wide field of applications: in defectoscopy, in the reception and sorting of the semi-finished goods, the highlighting of the superficial surface changes, thickness measurements, when examining the synthetic carbon fiber semi-finished products found in aviation and aerospace techniques. It applies to both ferromagnetic and non-ferromagnetic materials. The penetration depth being quite small method is indicated in the case of the high-precision defectoscopic control, the sensitivity range being within the limits of 0.01mm - 1mm, the working frequency being between 10Hz and 10MHz.
The control method with Eddy currents could be described as an interaction between several disciplines such as: theoretical physics, electrical engineering, electronics and metallurgy. Until recently, the Eddy current control technique was used only in the metal materials industries. In recent decades, it has begun to be used in the aerospace and nuclear industry. As with other non-destructive control methods, Eddy current tests allow the measurement of material properties and dimensions or the detection of discontinuities. In general, turbulent current control provides near-instantaneous measurement results.