Sensitivity of the Acoustic Impact Technique in Characterizing Defects/Damage in Laminated Composites

The sensitivity of the Acoustic Impact Technique (AIT) has been investigated in detecting delaminations, impact and moisture induced damage in laminated composites. The use of Acoustic Impact Technique has shown encouraging results by previous investigators in identifying defects like delamination and disbonds in honeycomb structures. Very limited work has been reported in the literature about the utility of AIT as a NDT tool for testing laminated structures. The present work investigates the sensitiveness of the AIT method in detecting delamination in laminated composites in terms of size, shape, position and degree of concentration. The technique has also been applied in identifying low velocity impact and moisture induced damage in laminated composites. The significant advantage of AIT is that this technique is attractive for field applications. The AIT method involves striking the structure with an instrumented impacter in the region of interest and recording the time history of the impulse. The response of the signals received from both good and defective zones of a specimen were anlayzed in the time domain. The experimental configuration used by previous investigators was very restrictive. In this study a different experimental set up for studying AIT is developed. The effectiveness of AIT was evaluated by making a comparative study with ultrasonic measurement in detecting similar types of defects. The results indicate the sensitiveness of AIT in detecting delamination in laminated composites in terms of size, depth and degree of concentration. The low velocity impact damage can also be identified using the AIT method. Moisture induced damage, shape of delamination and position of delamination along the edges and the center appear to be less sensitive for detection by the AlT method.