Multifrequency Eddy Current Inspection for Cracks Under Fasteners -Phase II.

摘要

This report describes the second phase of a two-phase program. Phase I, reported in TR-76-209, was directed toward the evaluation and demonstration of multiple frequency eddy-current (MFEC) using wing-splice samples and laboratory instrumentation to detect cracks under titanium and steel fasteners. This Phase II report covers the development evaluation of a prototype MFEC system for field use. The system was built around commercially available micro-computer modules coupled with in-house designed eddy current electronics, an eddy current probe, and a multifunction operator control panel. The system was 'trained' using two C-5A wing panel sections having sawcuts to simulate cracks. Tenth-inch sawcuts at the top of the second layer could be repeatedly detected using a decision algorithm based on a combination of four frequencies. The prototype system was evaluated during July, 1978, as part of the C-5A Structural Evaluation and Inspection Program (SEIP). Of approximately 400 fasteners inspected with the system, one suspect was found and later confirmed with another NDE method. In continued development of the MFEC technique, methods must be investigated which will be tolerant of variations in geometry found around rib stiffeners and single fastener rows. (Author)