Weld inspection by focused adjoint method.

This paper reports a methodology for the non-destructive ultrasonic evaluation of welds, based on probing, residue back-focusing and topological energy calculation using an enhanced (focused) adjoint method. The proposed method combines the advantages of time reversal to compensate for the cumulative distorsions experienced by a wave propagating in a heterogeneous medium, and topological imaging to highlight the defect location. The synergistic effect of this combined approach makes it possible to detect anomalies in the most efficient way. The method paves the way towards a matched-insonification imaging of anomalies in anisotropic media.

Topological imaging in bounded elastic media.

Detecting, imaging and sizing defects in a bounded elastic medium is still a difficult task, especially when access is complex. Adjoint methods simplify the task as they take advantage of prior information such as the geometry and material properties. However, they still reveal a number of important limitations. Artifacts observed on the conventional topological energy image result from wave interactions with the boundaries of the inspected medium. The paper describes a method for addressing these artifacts, which involves forward and adjoint fields specified in terms of the boundary conditions. Modified topological energies are then defined according to the type of analyzed flaw (open slit or inclusion). Comparison of the numerical results with the experimental data confirms the relevance of the approach.