Non-destructive inspection of adhesively bonded patch repairs using Lamb waves

Life extension of aging aircraft with adhesively bonded repair patches has received significant interest over the last 10–15 years. This repair method has several advantages over riveted patches since it introduces lower stresses in the repaired area and reduces weight. It is a promising repair technique, which can be also applied to composites, where the load transfer paths through mechanical fasteners can cause local damage. However, patch debonding might occur when the structure is loaded, and the damage might continue propagating in the substrate. As a result, a robust structural health monitoring system needs to be designed and implemented in order to continuously assess the integrity of the repaired area. This paper illustrates the non-destructive inspection with Lamb waves of a repaired aluminium flat plate with a bonded external patch. The damage developed was assessed with outlier analysis, which is a pattern recognition method.