Speaker
Description
Ultrasound-excited active thermography method, which is frequently referred as vibrothermography or sonic-IR, is a promising non-destructive testing (NDT) technique. This technique involves exciting high-power ultrasounds in the inspected object while observing the surface temperature using an infrared camera. The ultrasonic vibrations induce frictional heat in the defective region in the object, enabling defect detection by identifying abnormal temperature regions in the observed thermal image. This inspection principle makes this technique highly effective for detecting closed defects such as closed cracks or poor adhesion (which are difficult to detect using other NDT methods). However, this technique should not be suitable for detecting voids or delaminations with large opening widths. Therefore, this study focuses on ultrasonic-excited active thermography inspection for delaminations in carbon fiber reinforced plastics (CFRPs), and quantitatively investigates the conditions under which delamination becomes detectable based on the opening widths of the delaminations and ultrasonic wave propagation. Active thermography inspections were performed on CFRP specimens with artificial delaminations, and after the inspections, the specimens were cut to observe the opening widths of the delaminations. The authors demonstrated in a previous paper that the waves excited in the inspected object are guided waves (the A0 mode Lamb waves in plate-like objects). The experimental results showed that delaminations could be detected when the opening widths were similar to or smaller than the amplitude of the standing waves generated by the propagation of guided waves in the specimens. On the other hand, the delaminations having larger opening width could not be detected (but only the edges of the delamination areas could be detected). Such large-width delaminations were clearly detected by conventional pulsed thermography method using xenon flash lamps, which was performed for comparison. These results imply that the amplitude of the input ultrasound or the active excitation method itself should be changed depending on the opening width of the defect to be detected. Detailed discussions on the relationship between detectable defect conditions and the waves propagating in the objects will be presented at the conference. These findings should be a fundamental guide for setting inspection conditions in ultrasound-excited active thermography method.
