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An Edge of Light™ (EOL) computer vision-based system is used for detection and measurement of pillowing deformation in aircraft fuselage lap joints. Two approaches are described for the interpretation of the EOL images. The first approach is based on reconstruction of the inspection surface using the slope angle associated with each corresponding pixel. The second method uses image pattern with the principle component analysis. A simple device simulation corrosion pillowing named “pillowing simulator” is described and used to study the two approaches in terms of their quantification capability. Also, an algorithm to identify rivets in the EOL images is developed and presented in this paper. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Conventional eddy current and pulsed eddy current techniques were employed to detect hidden corrosion in aircraft structures. To quantify the inspection results, a function that relates the nondestructive inspection (NDI) measurements to the material thickness is required. Conventionally, a calibration curve is derived from the calibration procedure for each inspection method. To take advantage of the multiple NDI inspections, in this study, a generalized additive model (GAM) was adopted to correlate multiple inspections to the material thickness loss. A back fitting algorithm was used to fuse the complementary information from the multiple inputs through this model. To show the efficiency of the data fusion approach, the results were compared with those from individual inspection methods. The specimen used in this study is a two-layer lap joint from a service-retired aircraft. The study will clarify which individual inspection is most appropriate to characterize the top or the bottom layer corrosion and which combination of the inspections can achieve the best thickness estimation for the two layers respectively. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Damage tolerance-based operation and maintenance of aircraft components require the estimation of probability of detection (POD) of nondestructive inspection (NDI) techniques. The standard approach to estimate POD of an NDI process is to perform demonstration tests on simulated or real components. To generate a realistic POD, MIL-HDBK-1823 suggests that flaw sizes should be uniformly distributed on a log scale covering the expected range of the POD curve in the transition region. This paper presents an alternative approach that is based on Rayleigh distribution of flaw sizes on a log scale covering the expected range of flaws. This approach is only applicable to NDI methods that provide a signal response or “a⁁” for a given flaw size “a”. The use of this approach increases the accuracy of the POD estimate by optimizing the distribution of flaw sizes in the range of transition between very low and very high POD. The paper also presents a new three dimensional representation of POD versus the false call rate, defined by the relative operating characteristic (ROC). The 3D presentation makes it easier to visualize the change in POD and false call rate with the variation of decision threshold set for flaw detection. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

Eddy current testing methods are commonly used in the inspection of aircraft fuselage splice joints for corrosion and fatigue damage. However, the inspection of these components suffers from the spurious effects introduced by liftoff, interlayer gaps, rivets, and paint. To overcome these effects, multi-frequency eddy current testing has been proposed, but has not been widely employed due to the difficulty of correctly mixing the different signals. In this study, we investigated the potential of using a data fusion technique to combine the results of different frequencies and quantify hidden corrosion in service-retired aircraft lap splice joints. An updating mechanism based on a contextual Dempster-Shafer approach was used to combine probability mass values from multiple sources. The final classification results were obtained by making decisions based on the maximum belief of the fused results. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

Several key features of pulsed eddy current transient responses from probe coils have been identified and related to specific test parameter and material property changes. While many features are related to flaw size and location, most, such as maximum amplitude, are severely affected by probe liftoff variations and interlayer separations in multi-layered structures. We present several PEC signal features and interpretation techniques for locating and quantifying metal loss in calibration specimens and naturally corroded lap splices exhibiting common noise sources. [ABSTRACT FROM AUTHOR]