Borehole Inspection on Aircraft Structures using Multifrequency EC-Technique

摘要

The eddy current inspection of boreholes using rotating probes is a commonly used method for the inspection of aircraft structures. Typically a single frequency method is applied. Earlier investigations using a multifrequency system have shown better results in determination of the crack length from the eddy current signals. The latest developments resulted in a custom designed application for borehole inspections. It uses the four frequency technique with a standard rotating probe and a position encoder to allow the recording of the signals including depth information. To improve reliability, several helpful functions have been implemented. A data structure adapted to the inspection task allows easy archiving of the data. One of the main aims is the reduction of the human factor. Therefore, the application is equipped with an automatic adjustment procedure, as well as an automatic analysis algorithm. The analysis algorithm detects cracks and results in the determination of crack lengths based on the correlation obtained from several test series in the laboratory and on a A340-600 structure test. Furthermore, a schematic representation of detected cracks provides additional information to the user. The recorded signal scans can be analysed directly or for detailed investigations later in the office. Currently the system is put into practice for the A380 structure test, which takes place in Dresden.