Detection and characterization of high-velocity impact damage in advanced composite plates using multi-sensing techniques

Abstract

Advanced composites are increasingly used in aerospace, naval, and automotive vehicles due to their high specific strength and stiffness. However, the mechanical properties of composite materials may degrade severely in the presence of damage. Damage due to impact in composite plates is often difficult to detect using any single technique. In this paper, the use of multiple sensing techniques to characterize high-velocity impact damage in advanced composites is reported. Broadband wave-based acoustic emission (AE) sensors are used to capture wave signals due to impact while shearography and ultrasonic (UT) immersion techniques are used to assess location and extent of damage after the impact. Five 48-ply [0/+45/90/−45]6s laminated AS4/PEEK composite plates were used as test specimens. Shearography images of all five test specimens were taken before impact testing to detect any pre-existing internal damage from fabrication. Three broadband AE sensors were mounted on the surface of the composite plates to capture the AE signals due to impact. A 3/8-inch diameter stainless steel ball fired from a gas gun facility was used as a projectile to inflict damage to the composite plates. The AE signals were instantaneously acquired during the impact tests and stored in a computer. The AE signals show existence of both the extensional and flexural modes, with extensional modes typically showing first. AE energy also increases to a threshold as the kinetic energy of impact increases. Shearography fringe patterns show existence of damage and this is confirmed and quantified with C-scan images from the UT immersion test. There is good correlation between AE parameters such as AE energy, AE amplitude, and AE count with impact energy and with damage on the composite plates. Due to the low contrast of the shearograms, UT C-scans are used to show extent of damage. This research demonstrates how multiple sensing techniques can be used to characterize high-velocity impact damage in advanced composites.