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

Abstract

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 nondestructive 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.

Novelty detection and dimension reduction via guided ultrasonic waves: Damage monitoring of scarf repairs in composite laminates

“…The effect of noise was tested which showed that OA can detect damage even in extremely noisy environments (SNR = 19). However, in the work by Pavlopoulou et al (2012a) OA exhibited a nonmonotonic behavior with the increasing damage which has been further studied and explained in the current work. For that purpose PCA was employed as a well-established technique, through which the drop in the Mahalanobis squared distance was explored even though the damage propagated.…”

“…As previously investigated by Pavlopoulou et al (2012a) there are certain cases where the introduced damage to the structure is considerable enough to cause a significant signal time shift. This was demonstrated through an OA on an aluminum repaired panel that was subjected to fatigue loading and which identified unexpected behavior which is discussed and explained in the current work.…”

“…OA proved to be the fastest technique, however, the assumption that the normal condition data follow a Gaussian distribution is not present in the other methods. Finally, Pavlopoulou et al (2012a) performed OA in order to detect crack propagation and the debonding of an external patch in an aluminum repaired structure, with significant success. However the Mahalanobis squared distance exhibited a slight drop in cases where damage kept increasing, a complication which will be further examined in this work.…”

Evaluation of instantaneous characteristics of guided ultrasonic waves for structural quality and health monitoring

“…Successful applications involve several engineering case studies based on high‐dimensional data sets . However, in complex structures that are subjected to extensive loading, novelty detection methods can potentially give false alarms .…”

“…This can occur if the ultimate shear strain of the adhesive is exceeded under loading. Previous research on this subject has utilised novelty detection methods to detect damage when a metallic repaired structure was subjected to cycling loads .…”