Nondestructive evaluation of corrosion damage of Al-alloys by in-situ AE monitoring and nonlinear elastic wave spectroscopy testing

Significant amount of corrosion damage was revealed during recent complete inspections of airplane structures after years of service. The corrosion damage was located inside airplane’s hull and remained undetected until reaching hull’s outer surface. Therefore a demand for means of timely detection and non-destructive evaluation of corrosion damage arose. This work investigates the possibilities of monitoring on-going corrosion process by acoustic emission (AE) and of determining overall corrosion damage by the nonlinear wave modulation spectroscopy method (NWMS). Specimens made of Al-alloy L-beams simulating stringer reinforcements of airplane structure were studied. The samples were repeatedly immersed in sea salt solution. The acoustic emission activity was recorded in situ during corrosion process. Nonlinear parameters of the samples were measured in between corrosion tests by NWMS method. The current dynamics of a corrosion process was determined by AE, the amount of corrosion damage was corresponding to the nonlinear parameters obtained by NWMS. Since both methods can use the same type of piezoelectric transducers, they form a convenient part of a structure health monitoring system.