Reliability Assessment of Nondestructive Evaluation via Eddy-Current Model-Based Inversion

The reliability of nondestructive evaluation (NDE) techniques is currently determined through probability-of-detection (POD) studies that rely on measurments of actual hardware copies of representative flaws. There is now a need to eliminate the inefficiencies and expenses of this method by using model-based standards derived from sophisticated engineering computer codes, that are, in turn, derived from rigorous applications of physical theories. This proopsal applies the concept of model-based inversion that is based upon Victor Technologies' well-known eddy-current code, VIC-3D(c), to solve the problem of reliably assessing NDE techniques. We will introduce the notion of `Probability of Inversion,' and show that the classical model-assisted POD (MAPOD) becomes a simple corollary to it. Furthermore, we will develop a rigorous electromagnetic model for anisotropic media, such as Ti-6Al-4V, which is a titanium alloy that is widely used in aerospace structures and engines. With these concepts we effectively enter the `digital age' of eddy-current NDE, leaving traditional emphasis on analog instruments behind.