Günter Zenzinger

Thermographic crack detection by eddy current excitation

Eddy current thermography is a new NDT-technique for the detection of cracks in electroconductive materials. It combines the well established inspection techniques eddy current testing and thermography. The advantage of this method is to use the high performance of eddy current testing without the known problem of the edge effect. Especially for components of complex geometry this is an important factor which may overcome the increased expense for inspection set-up. The principle of this technique and an algorithm to increase the sensitivity for small defects are described. Some inspection examples on aero engines parts are presented which show the potential of eddy current thermography.

Optimized Image Processing for Eddy Current‐Thermography

Eddy Current‐Thermography is a well known NDT‐technique for the detection of open and hidden cracks in metallic parts. Cracks disturb the induced eddy currents and generate therefore characteristic temperature profiles. These temperature profiles are visualized by a thermographic camera. But, there is a problem arising from the fact that the heat produced by the eddy current coil itself is very inhomogeneous. This inhomogeneous heat transfer masks the temperature of the crack especially when inspecting complex shaped parts. This masking can be removed effectively by using a Fourier transform algorithm focused on a specific region in the temperature — time behavior of the heated surface. The processed final images are of binary form and easy to evaluate automatically. Eddy Current‐Thermography and this image processing were optimized for some aero engine parts. The reliable and automated detection of cracks at these parts show the great potential of this technique.