Volume 21, Issue 5 (September 1993)
Characterization of Defects in Graphite Fiber Based Composite Structures Using the Acoustic Impact Technique (AIT)
Acoustic Impact Technique (AIT), commonly known as “coin-tapping,” has been applied by previous investigators as a nondestructive evaluation technique to study disbonds in composite honeycomb structures. The experimental configuration adopted by previous investigators was somewhat restricted. In this study, a different approach to AIT is developed. This was done to overcome the experimental constraints encountered in the previous approaches. This paper presents experimental results obtained in the evaluation of defects commonly found in graphite based composite structures, such as delamination, fiber breakage, and misaligned fibers. The experimental approach adopted in this work has two main features. Primarily, the force-time history of the specimen's response to a low magnitude input pulse in different regions of the specimen is compared. Secondly, an Acoustic Emission (AE) wide band sensor was used in conjunction with the conventional acoustic impact technique. The combination of the AE sensor and AIT enabled the study of the material interaction with stress waves generated in the vicinity of the tapped region. Gross defects such as delaminations were identified through the change in the pulse width of the force input, while defects such as fiber breakage and misaligned fibers were successfully identified using AIT in conjunction with AE.