Abstract
The microscopic size and the closed characteristics of zigzag line defects at the root of friction stir welded joints frequently result in a detection inability by off-the-shelf ultrasonic weld inspection techniques. To overcome this problem, we take advantage of a non-linear ultrasonic approach by employing a slanted contact pitch-catch mode scanning using chirp-coded excitation with subsequent pulse-inversion analysis. We validated that the observed nonlinearity correlates well with the micro-crack density along the weld path. Doing so, hot spots in the pulse-inversion chirp-coded weld harmonic images can be interpreted as zones with high concentrations of micro-flaws.
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