Uncertainty Evaluation of Crack Sizing Capability Incorporating Model-based Inversion Applied to Bolt-hole Eddy Current Inspections

There is a need for innovative methods to provide accurate sizing of discontinuities in structures, to guide maintenance actions and better inform engineering of the structure state. This paper highlights the development of the capability to size the length and depth of cracks in multilayer fastener sites using bolt-hole eddy current (BHEC) techniques. Technical efforts include improvements to model calibration, liftoff compensation, and the inversion process. In addition, an expanded set of surrogate models was developed that address crack sizing for titanium, aluminum, and steel structures across multiple frequencies and for varying hole diameters. A comprehensive crack sizing evaluation study was performed under a wide range of test conditions, demonstrating improved sizing capability over using peak amplitude. Crack length estimates were found to have less error than crack depth estimates, although crack depth is the more critical parameter for informing maintenance actions.