Impact Monitoring in Aerospace Panels via Piezoelectric Rosettes

Abstract

This paper investigates the monitoring of impact damage in aircraft panels by the measurements of the resulting Acoustic Emissions (AEs) by Piezoelectric Rosettes. It has been recently demonstrated that the Piezoelectric Rosettes are essentially the dynamic equivalent of the Electrical Resistance Strain Gage Rosettes if certain conditions between the AE wavelength and the gage dimensions apply. Therefore, the Piezoelectric Rosettes can extract the principal strain angle of the AE wave, that is the wave propagation direction, without knowledge of the wave velocity. By intersecting two directions, the location of the AE source can be determined by a minimum of two Rosettes. Since no wave velocity is required, the AE source location is more accurate than conventional time-of-flight triangulation for complex structures where the wave velocity changes along different propagation directions (anisotropic materials) or along each propagation direction (tapered or layered geometries). The Piezoelectric Rosettes designed here are comprised of highly-flexible Macro-Fiber Composite (MFC) Piezotransducer patches that are conformable to curved surfaces and more durable than monolithic PZT sensors because they are less brittle. In this paper, the MFC Piezoelectric Rosettes are applied to monitoring the progression of damage during “blunt” impact tests of two curved carbon/epoxy composite panels with co-cured stringers and mechanically fastened shear-ties that are highly representative of aircraft fuselage structures. The damage progression was monitored satisfactorily without knowledge of the wave velocity in the panels and outside of certain time windows where the Rosette signals were saturated by the large impact loads. Additional impact tests are being planned to continue the development of this innovative impact monitoring technique.