Nondestructive Evaluation (NDE) Technology Initiatives II Delivery Order 0001: Multi-Layer Cracks and Multi-site Damage NDE

Abstract : This report describes the exploitation of the attractive performance of magnetoresistive (MR) sensors for NDE of metallic aircraft structure, into an imaging array for rapid scanning, and the demonstration of the performance of that array. There were a number of issues requiring resolution for this development. These included array geometry, excitation geometry, signal processing, software, calibration, and operation. The geometry chosen was a linear array with sensitivity axis normal to the surface being scanned, and the excitation geometry is that of a uniform current "sheet". The array has been initially demonstrated on several test samples, and shown to be able to detect small flaws/cracks at depths of upwards of one-half inch. In many cases, cracks with length only a fraction of the covering metal are easily seen with no additional data manipulation. The array has been integrated and demonstrated with the MAUS scanning platform. Because of the chosen geometry, dependence on circular symmetry is obviated, and therefore rapid scanning along a row of fasteners is possible, with real time imaging. In the future, the bounding of applicability of the array for Air Force inspection scenarios must be determined, as well as flaw signature enhancement through additional processing.