Thermo-inductive crack detection

In the case of thermo-inductive testing the material is heated by induced eddy currents and the emission from the material surface is detected by an infrared camera. Anomalies in the surface temperature correspond to in-homogeneities in the material. Experiments show that for magnetic steel the edges of surface cracks become visible through higher temperatures. In contrast, in non-magnetic materials one observes lower temperatures around a surface crack. An analytical and a semi-analytical model are presented to calculate the eddy current distribution and the temperature distribution for different cases. Results for magnetic and non-magnetic materials are compared, showing how the temperature depends on the material parameters, on the penetration depth of the eddy current and on the crack depth. The comparison of the calculated and measured results shows a very good agreement. Additionally, some applications are presented, where the thermo-inductive testing method has been used in laboratory and in industrial environment.