NDT assessment of bonded assemblies - Image optimization for weak bond characterization using ultrasonic array transducer

Compromised interface bonds in structural components can lead to premature loss of structural integrity. Such defects are very difficult to detect using traditional acoustic inspection techniques. We assess the ability of linear ultrasonic Non-Destructive Testing (NDT) methods to detect or differentiate between weak-kissing bonds from healthy ones, by using a set of contaminated and non-contaminated bonds. An Ultrasonic Array Transducer (UAT) enables increased informational content, hence they have been used to detect and differentiate compromised bonds. Considerable research has been made into detecting weak bonds, but a practical, cost effective and industrially applicable solution remains elusive. The key problem is the signal changes are small, therefore we have developed an iterative testing methodology, in which the experimental variation in each of the following steps is significantly reduced: Sample Preparation; Data Acquisition; Imaging[1, 2]; Feature Analysis[3, 4]; Characterization/Classification; Interpretation. Our research addresses the issues related to UAT measurement techniques, specifically Full Matrix Capture (FMC)[1, 2] and Total Focusing Method (TFM)[1, 2], Scattering Matrix(derived) [3, 4] extraction in time domain, and other related or derived methods. Here the optimization of bondline imaging, resulting in higher quality and coherence of the imaging, is presented and discussed.