A comparatively recent technique that has shown some promise in the field of debond/delamination evaluation is the acoustic impact technique (AIT). It has been demonstrated successfully that AIT is capable of detection and location of debond defects in isotropic materials and all metal, mutually bonded components. AIT is the proverbial old wine in new bottles. It stems from the age old technique used by house wives and potters alike, which went under the name TAP TEST or the COIN TAP TEST. In AIT the erstwhile crude and subjective testing method has been automated and subjected to electronic data processing. Both these improvements have helped in rendering the results repeatable, quick to apply, accurate and, most important, independent of the operator and, hence more objective.

Four CFRP laminates of 20 layers each were studied. Two laminates were damaged by subjecting them to different energy levels of impact, while one laminate had flaws introduced in it at the time of manufacture itself. The remaining CFRP laminate was unimpacted and free of flaws. All the four laminates were scanned using the ultrasonic C-scan, which served as a reference. Subsequently, these laminates were subjected to AIT and the results obtained by two techniques were compared. Once a yardstick was established, AIT was employed to detect flaws on Ka-28 composite main rotor blade.

Investigations have been carried out on CFRP panels containing defects of different types and sizes, using the acoustic impact generator in association with the FFT analyzer for analysing the signals in the frequency domain