A scanning spatial-wavenumber filter and PZT 2-D cruciform array based on-line damage imaging method of composite structure

Abstract

The spatial-wavenumber filtering technique of Lamb wave is gradually applied for damage inspection of composite structure in recent years because it is an effective approach to distinguish the wave propagating direction and mode. But for on-line damage monitoring of composite structure by using spatial-wavenumber filter, the problem is how to realize the spatial-wavenumber filtering of Lamb wave when the wavenumber response cannot be measured or modeled. This paper proposes a scanning spatial-wavenumber filter and piezoelectric sensor (referred to as PZT) 2-D cruciform array based on-line damage imaging method of composite structure. In this method, a 2-D cruciform array constructed by two linear PZT arrays is placed on composite structure permanently to acquire Lamb wave damage scattering signal on-line. For one linear PZT array, a scanning spatial-wavenumber filter which does not rely on any modeled or measured wavenumber response is designed to filter the damage scattering signal at a designed wavenumber bandwidth to give out a wavenumber-time image. Based on the image, the wavenumber of the damage scattering signal projecting at the array can be obtained. The same process can be also applied to the other linear PZT array to get the wavenumber projecting at that array direction. By combining with the two projection wavenumbers, the damage can be localized without blind angle. The method is validated on an aircraft composite oil tank of variable thickness. The validation results show that the damage direction estimation error is less than 2° and the damage distance estimation error is around 20 mm in the monitoring area of nearly 600 mm × 300 mm. It indicates an acceptable performance of the damage imaging method for complex composite structure.