The application of Fermat's principle for imaging anisotropic and inhomogeneous media with application to austenitic steel weld inspection

Ultrasonic inspection in anisotropic and inhomogeneous media has long presented a challenge because of the complex steering of ultrasonic paths. An approach is presented in which the true geometry of a previously used austenitic steel weld model is distorted so that, from one viewing location, all ultrasound travels in straight lines with a constant isotropic velocity. The mapping from the real space to this distorted space is accomplished using Fermat's theorem of least travel time applied through ray tracing. Applications specific to inspection design and data interpretation for manual ultrasonic inspection of welds in austenitic steel plates are given. Validation of some intermediate results is provided using finite element analysis.