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

Advanced composites are increasingly used in aerospace, naval, and automoti ve vehicles due to their high specific strength and stiffness. However, the mechanical properties of composite materials may degrade severely in the p resence of damage. Damage due to impact in composite plates is often diffic ult to detect using any single technique. In this paper, the use of multipl e sensing techniques to characterize high-velocity impact damage in advance d composites is reported. Broadband wave-based acoustic emission (AE) senso rs are used to capture wave signals due to impact while shearography and ul trasonic (UT) immersion techniques are used to assess location and extent o f damage after the impact. Five 48-ply [0/ + 45/90/ - 45]6s laminated AS4/P EEK composite plates were used as test specimens. Shearography images of al l five test specimens were taken before impact testing to detect any preexi sting internal damage from fabrication. Three broadband AE sensors were mou nted on the surface of the composite plates to capture the AE signals due t o impact. A 3/8-inch diameter stainless steel ball fired from a gas gun fac ility was used as a projectile to inflict damage to the composite plates. T he AE signals were instantaneously acquired during the impact tests and sto red in a computer. The AE signals show existence of both the extensional an d flexural modes, with extensional modes typically showing first. AE energy also increases to a threshold as the kinetic energy of impact increases. S hearography 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 th e low contrast of the shearograms, UT C-scans are used to show extent of da mage. This research demonstrates how multiple sensing techniques can be use d to characterize high-velocity impact damage in advanced composites. (C) 2 001 Elsevier Science Ltd. All rights reserved.