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Non-destructive evaluation (NDE) is a groundbreaking
science that could greatly advance adhesives and sealants. NDE conveys
"proof of reliability" to engineers and designers that a bond joint is
properly constructed and reliable. It can provide an early warning of
defective adhesively-bonded structures without having to physically break
the bond apart to assess its maximum hold strength.
To further this area of scientific advancement, ASC partnered with Virginia
Tech for NDE research that involves the testing of a high resolution ultrasonic
technology, which was previously successful in detecting flaws in aerospace
composite materials.
Status:
Although the research project did not work out as originally planned due to the inability of the ultra-high resolution Phlite technique to reliably discriminate among good and defective bonds, a number of insights were gained into the technology. Successful applications of the Phlite approach to medical, sensing, and cure of thicker sealant joints suggests that the technique as merit for practical industrial applications. The studies involving propagation of ultrasonic waves along single lap joints as guided waves proved infeasible because of the complex wave path and the integrated signal obtained. Point-by-point evaluation (e.g. in a C-scan mode) of single lap joints offered potential for obtaining localized information about bond quality, but the frequency limits of the equipment proved inadequate to properly resolve the signals associated with propagation in the very thin bond line, resulting in output that could not be effectively deconvoluted. Increasing the ultrasonic frequency by about an order of magnitude is technically feasible and could result in a technique that could work for bonded joints. Nonetheless, the ability to determine a reliable locking point on the wave envelope remains challenging and distortion of the envelope can lead to ambiguity in the results. Although the technique offers promise for some applications, challenges remain in adapting it to robust application in the nondestructive evaluation of structural adhesive joints. The research has confirmed the exceptionally good resolution of the technique for discerning time of flight of ultrasonic signals, but also the limitations of understanding the outputs and translating these into meaningful correlation with joint properties for thin bondlines.
Additional Resources:
NDE Q&A
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