Considerations in the validation and application of models for eddy current inspection of cracks around fastener holes

To improve the detection and characterization of cracks around fastener holes in multilayer structures without removing the fastener, model-based approaches are proposed to support the design of advanced eddy current (EC) NDE systems. This work demonstrates the validation and application of models to simulate EC inspection as part of the design process. The volume integral method (VIM) and finite element method (FEM) are both used to simulate eddy current inspection of fastener sites for fatigue cracks. Convergence studies, validation with existing models, experimental validation studies and validation through inverse method demonstrations are presented, providing a continuum of methods to ensure the quality of measurement models. Consideration concerning convergence and validation is also given with features sensitive to the sample geometry and flaw characteristics. A novel calibration technique is also presented to practically evaluate the transformation between model-based impedance calculations and experimental voltage data. A series of studies are presented concerning the detection of cracks around fastener holes demonstrating the quality of the simulated data to represent experimental measurements.