Study the effect of engagement force of ultrasound transducer on crack detectability in sonic IR imaging

Sonic IR imaging has been shown broad applications for detecting different types of defects in various materials. The principle of this technology is rather simple. The natural occurrence of acoustic chaos can increase the IR signal level and enhance the defect detection. This is due to the non-linear coupling between the ultrasound transducer and the target. In last year's QNDE, we presented the results from studying the effect of coupling materials in Sonic IR Imaging. We have shown the results with several coupling materials and quantitatively distinguished their different levels of effect on the detectability of a defect. We continued our study on this non-linear coupling issue. In this paper, we present our results on how engagement force between the ultrasound transducer and the target will also affect crack detectability. Correlation between the acoustic energy and the thermal energy in the crack of an aluminum sample is analyzed and discussed as well.