Using the Foerster Rivet Check System to Detect Cracks Under Installed Fasteners

Abstract : The Foerster Rivet Check system is an instrument designed to detect cracks under installed fasteners in relatively thin layers of an aircraft skin. Its operation is based on a rotating self-nulling eddy current probe. It was found that the system is able to detect relatively small cracks under non-ferrous fasteners at depths up to 0.12" in layers of aircraft skin. The amplitude of its' output signal is proportional to flaw size and it is able to indicate the relative position of flaws. Interference from the presence of ferrous fasteners results in false indications. At present the system works well in the laboratory on flat surfaces, but modifications are required to make it more suitable for use under field conditions.