Laser Bond Inspection Device for Composites: Has the Holy Grail Been Found?

Originally published in NTIAC newsletter: Volume 30, No. 2, June 2005.

Authored by Richard H Bossi, Kevin R Housen, and Craig T Walters

SUMMARY
Extensive experimental development, supported by 1-and 2-D hydrodynamic code simulations has demonstrated that the strength of bonds can be tested using calibrated weak shock waves (stress waves) generated at the surface of composite (and other) joints. Previously full-scale roof testing of bonded structure has been the only sure method of detecting “kissing” or weak bonds. Laser bond inspection (LBI), using high-intensity stress waves, has been shown to provide a method for localized testing of bond strength.
Controlled stress waves of sufficient intensity have been shown to be useful for adhesion evaluation. Gupta, et.al. demonstrated that internal bonds could be evaluated with shock waves [3-5]. Recently, high peak power, short burst laser systems have been shown to reliably and repeatedly test the strength of internal bondlines in composite joints of reasonable (6 to 15 mm total thickness) [6]. Modeling of the method has shown that the laser beam shape results in controlled, very localized testing of bond strength. A compact high peak power laser system and team delivery method has been designed for factory implementation. To date, numerous tests on composite to composite bonds have shown the method to be sensitive to weak bonds created by
poor adhesive mixing, improper surface preparation and/or contamination.

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