Health Monitoring of Stiffened Metallic Plates Using Nonlinear Wave Interaction and Embedded PZT Transducers

Abstract

AbstractThe ultimate strength of a structural component can be limited in the presence of microscopic imperfections, which serve as the origin of damage process. These micro imperfections are considerably shorter than the acoustic wavelength of the frequencies normally used in ultrasonic nondestructive technique. As a result, the sensitivity of the linear acoustic characteristics (attenuation, velocity etc.) is not sufficient enough to detect the microscopic imperfections of a structure. But, these micro imperfections produce local excess nonlinearity, which is higher than the intrinsic nonlinearity of the intact structure. On the other hand, weakly or incompletely bonded interfaces (e.g., contact-type defects, cracks, debondings, delaminations and loosening in bolted joints) also exhibit highly nonlinear behavior as the contact area changes frequently when elastic waves propagate through the interface. The various nonlinear techniques for damage detection developed in the recent years are: non-linear resonant ultrasound spectroscopy (NRUS) and non-linear wave modulation spectroscopy (NWMS).The later consists of two methods, namely harmonics generation and sidebands generation. In this work a simulation study has been carried out using ANSYS Finite Element (FE) software, where the NWMS methodology is adopted for the case of a stiffened aluminum plate for different degrees of damage in the form of different delamination lengths. A damage index (DI) is defined by taking into account the relative amplitude of the harmonics or the side-bands with respect to the carrier frequency amplitude. It is found that the DI increases with the increase in delamination length.KeywordsNonlinear wave interactionContact-type defectsNon-linear wave modulation spectroscopyStiffened plateDelaminationStructural health monitoring