Damage detection in foam core sandwich structures using guided waves

Abstract

Sandwich structures, consisting of two face sheets and an intermediate foam core, have a high potential in aerospace applications. However, they are rarely used because it is difficult to inspect them by the conventional non-destructive techniques. Indeed, non visible damage of the sandwich face sheets can in fact be accompanied by a large skin/foam core delamination. This paper describes a new approach to detect sub-interface damage in such structures by using ultrasonic guided waves. These waves are excited with a PZT disc permanently bonded on the structure and their interaction with foam core damages is detected by scanning the structure with an air-coupled transducer. To carry out this monitoring technique, the first step was to analyse the propagation of waves guided in such sandwiches with both numerical and experimental tools. This allowed selecting the specific waves and their frequency which will be the most sensitive to skin/foam core delaminations and to make easier the interpretation of the measured waveforms. Finally, an adapted signal processing was implemented in order to localize and to characterize delaminations in sandwich panels.