Model-Based Parametric Study of Surface-Breaking Defect Characterization Using Half-Skip Total Focusing Method

Abstract

As the demand of structural integrity in manufacturing industries is increasing, the ultrasonic array technique has drawn more attention thanks to its inspection flexibility and versatility. By taking advantage of the possibility of individual triggering of each array element, full matrix capture (FMC) data acquisition strategy has been developed that contains the entire information of an inspection scenario. Total focusing method (TFM) as one of the ultrasonic imaging algorithms, is preferably applied to FMC dataset since it uses all information in FMC to synthetically focus the sound energy at every image pixel in the region of interest. Half-skip TFM (HSTFM) is proposed in multi-mode TFM imaging that involves a backwall reflection wave path, so that the defect profile could be reconstructed for accurate defect characterization. In this paper, a method involving Snell’s law-based wave mode conversion is proposed to account for more reasonable wave propagation time when wave mode conversion happens at backwall reflection in HSTFM. A series of model based simulations (in software simSUNDT) are performed for parametric studies, with the intention of investigating the capability of defect characterization using HSTFM with varying tilt angle and relative position of surface-breaking notch to array probe. The results show that certain TFM modes could help with defect characterization, but the effectiveness is limited with varying defect features. It is inappropriate to address a certain mode for all characterization perspectives but rather a combination, i.e., multi-mode TFM, should be adopted for possible interpretation and characterization of defect features.

Imaging of vertical surface-breaking cracks in concrete members using ultrasonic shear wave tomography

“…This undesired, strong signature is a result of the aggregated finite bands of reflections from the specimen back wall (i.e., it is a back wall artifact). Similar patterns in HSTFM images have also been reported in previous research 39 , 40 , 49 on FMC datasets from metallic components. The inclined pattern of the signature observed here is due to the Half Matrix Capture of the array transducers, where all elements transmit individually but only those elements, which did not emit in the previous transmission act as receivers.…”

“…As all images were normalized to their maximum amplitude the visibility of the defect signature is improved. Such strategies to suppress the strong artifacts which are caused by the direct back wall reflections in Half-Skip images have also been reported earlier 49 .…”