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This paper introduces spatial decomposition algorithms to the volume integral method, which will enable the integral equation method to efficiently solve electromagnetic scattering problems where the scatterer extends across several layers or multiple scatterers exist in multiple layers. Model comparisons with the finite element methods are used validate the approach. Studies of typical aging aircraft eddy current inspection problems are conducted using the new formulation. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

A series of numerical studies using validated models are presented investigating the influence of probe design and geometric flaw parameters on the eddy current measurement response for the inspection of cracks around fastener holes in multi-layer structures. Multiple quantitative features of the eddy current data were evaluated. The goal of this study is to demonstrate the influence of these design parameters on the ability to resolve the flaw characteristics in the measurement data. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Previous work on the detection of cracks around fastener holes in multi-layer structures using eddy current NDE has met with some success; however, challenges remain in detecting smaller corner cracks while minimizing false call rates. To address this issue, a 3D model was developed for this problem and successfully validated with experimental data. Using this model, a series of numerical studies were performed to identify potential features for defect classification. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

This paper investigates the possibility of crack detection for holes containing elastic inserts. A BEM model was formulated for the scattering response of an incident shear wave transducer signal by a cylindrical hole with a radial notch, an elastic insert, and a stiffness interface between the hole and the insert. Through simulated and experimental studies, certain interface conditions were identified for which significant interface waves can be generated and subsequently used for inspection purposes. [ABSTRACT FROM AUTHOR]

In earlier work, an automated protocol was considered to detect bottom cracks in weep holes. During experimentation, this protocol was found to produce some false calls and miss certain small cracks. In this paper, a technique is presented which examines the variation in the A-scan signals as the transducer is incrementally moved along the wing surface. The advantage of this B-scan classification technique is its ability to detect superimposed signals independently from the shape of the pulse. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Weep holes are incorporated in the risers of wing structures in C-141 aircraft to allow fuel to be properly distributed during flight. Two types of fatigue cracks have been observed emanating from weep holes, top cracks that emanate upward and bottom cracks that propagate toward the wing surface. A new approach using creeping Rayleigh waves has been shown to be successful in detecting top cracks in weep holes. The focus of this paper is the development of a robust automated protocol for the detection of both top and bottom cracks in weep holes. A numerical technique was developed using the boundary element method (BEM) to calculate simulated waveforms for reflection and backscattering of ultrasound from weep holes with top or bottom cracks. The simulations were validated by comparison with experimental results. From parametric studies of this model, a robust protocol incorporating both the pulse echo and pitch catch creeping Rayleigh wave signals from top-cracks was defined. Protocols incorporating neural networks were developed for both top and bottom crack classification. A complete automated procedure for crack detection was successfully trained with both simulated and experimental data and was verified with experimental data for the expected variation in weep hole size and crack length. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]