Passive guided wave tomography for SHM applications

Mesnil, Olivier; CEA; France

Chapuis, B.; CEA, LIST; France
Druet, T.; CEA; France

ID: ECNDT-0304-2018
Session: Guided Waves techniques 3
Room: G3
Date: 2018-06-15
Time: 09:20 - 09:40

Structural health monitoring (SHM) consists in embedding sensors in a structure like an aircraft or a naval ship in order to detect defects (for example corrosion) before a serious fault occurs in the structure. Guided elastic waves – which have the ability to propagate over long distances – emitted by a sensor and propagating to another one are often used as the physical way of detecting the defect. 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 tackle this constraint is to use passive techniques based on the use of the ambient acoustic noise in place in the structure. It has been shown that, under certain conditions, transient response between two sensors can be estimated from those passive techniques.

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 comparisons between results obtained with both active and passive techniques with the aim of doing passive tomography of extended defects (such as corrosion) using an array of piezoelectric (PZT) transducers. Noise is generated thanks to compressed air sprayed on the surface of an aluminum plate. Experimental results using passive tomographic algorithms will also be shown and described. Finally, an extension of this technique using purely passive guided wave sensors such as Fiber Bragg Grating (FBG) will be presented. Comparisons between PZT results and FBG results will be presented with the aim of noticing the possible advantages of FBG compared to PZT.