Eddy current testing of CFRP/Aluminium honeycomb sandwich structure

Aluminium honeycomb sandwich structure with CFRP panels has broad applications in aerospace and other industries. This paper presents an experimental study on the eddy current (EC) testing of such structure. An EC probe consisting of two pancake coils, one up and one down, is used for the testing and the amplitude of the differential voltage of the coils at each position of probe scanning is measured. The result of linear scan shows that the local minimal EC responses correspond to the edges of the core walls. In the C-scan results, different types of defects in the honeycomb cores including wall fracture, node disconnection, and core wrinkle can be identified. Threshold processing is performed to improve the indication of the defects. Topological graph of honeycomb core is obtained by connecting the pixels of C-scan image at which the EC responses are the local minima. Detection of impact damages is carried out and the effects of impact energy on the C-scan image are analysed. When the impact energy is increased, the part of the image in the area of damage becomes more blurred, and the minimal signal decreases monotonically. The area of damage seen in C-scan image is not necessarily increased with the increase of impact energy.