Passive SHM System for Corrosion Detection by Guided Wave Tomography

Abstract

Guided elastic waves emitted by a sensor and propagating to another one are often used as the physical way of detecting the defect in Structural Health Monitoring (SHM) systems of plate-like structures. However, the implementation of SHM systems is restricted in many situations by the necessity to store or to harvest the electric energy necessary to emit the waves. A promising way to overcome this constraint is to use techniques based on the cross-correlations of the ambient noise in place in the structure. The idea is to take advantage of the elastic noise naturally present in the structure (due to engine vibrations or aero-acoustic turbulences on the fuselage of an aircraft for example) in order to avoid the emission of the elastic waves by the SHM system. The complexity of the embedded SHM system is therefore reduced. We present here studies of noise cross-correlation techniques that have been conducted with the aim of doing passive guided wave tomography of extended defects (such as corrosion) using an array of piezoelectric (PZT) transducers. Noise is generated by spraying compressed air on the surface of a thin aluminum plate. Passive measurements are compared to active signals to demonstrate the effectiveness of the cross-correlation technique. Experimental results which come from tomographic time-of-flight imaging algorithms will also be described. Finally, an extension of this technique using Fiber Bragg Gratings (FBG) optic sensors will be presented.

V-1670-15