High-Precision Noncontact Guided Wave Tomographic Imaging of Plate Structures Using a DHB Algorithm

Abstract

The safety diagnostic inspection of large plate structures, such as nuclear power plant containment liner plates and aircraft wings, is an important issue directly related to the safety of life. This research intends to present a more quantitative defect imaging in the structural health monitoring (SHM) technique by using a wide range of diagnostic techniques using guided ultrasound. A noncontact detection system was applied to compensate for such difficulties because direct access inspection is not possible for high-temperature and massive areas such as nuclear power plants and aircraft. Noncontact systems use unstable pulse laser and air-coupled transducers. Automatic detection systems were built to increase inspection speed and precision and the signal was measured. In addition, a new Difference Hilbert Back Projection (DHB) algorithm that can replace the reconstruction algorithm for the probabilistic inspection of damage (RAPID) algorithm used for imaging defects has been successfully applied to quantitative imaging of plate structure defects. Using an automatic detection system, the precision and detection efficiency of data collection has been greatly improved, and the same results can be obtained by reducing errors in experimental conditions that can occur in repeated experiments. Defects were made in two specimens, and comparative analysis was performed to see if each algorithm can quantitatively represent defects in multiple defects. The new DHB algorithm presented the possibility of observing and predicting the growth direction of defects through the continuous monitoring system.

Comparison of Ultrasonic Non-Contact Air-Coupled Techniques for Characterization of Impact-Type Defects in Pultruded GFRP Composites

“…The unfiltered reconstructed image was obtained using the linear interpolation, while the filtered image is obtained using the shape-preserving interpolation with the Hann filter. In the reconstructed images, an image artefact due to the boundary of the scan was observed, as mentioned in [30]. However, these edge artefacts did not influence the quality of the reconstruction because of the large The reconstruction algorithm was performed using the inverse Radon function that is available in the MATLAB image processing library.…”

“…Sinograms can be mathematically solved using different techniques [ 42 ] such as the traditional filtered back projection (FBP) algorithm, reconstruction algorithm for the probabilistic inspection of damage (RAPID), and difference Hilbert back projection (DHB) algorithm. The RAPID algorithm is not suitable for multi-defect imaging and is best used to visualize faults with fewer transmission and reception points [ 30 ]. These limitations can be overcome using the FBP algorithm, where the image precision is better, and it is well suited for multi-defect imaging; the only disadvantage is the visual artefacts, occurring near the scanning edge, where the information is distorted.…”

“…There were studies on ultrasonic tomography using contact transducers [ 26 , 27 , 28 , 29 ] which showed promising results with faster solutions; however, the biggest downside is that, for these contact techniques, the transducers are fixed at a permanent position, which offers a structural health monitoring solution, but is not suitable for in situ inspections. Another recent study was performed [ 30 ] using laser excitation; the air-coupled approach was used for isotropic materials and various tomographic reconstruction algorithms were discussed.…”

Ultrasonic Methods

“…To get the desired resolution, a large number of projections are required which can be collected either using transmission or reflection approach. Among the sensor arrangement topologies, the crosshole, doublecrosshole and fan-beam are the most popular ones (Park et al 2020). Several different tomographic reconstruction techniques exist, namely straight-ray, bent ray and diffraction tomography (Belanger and Cawley 2009;Willey et al 2014;Belanger et al 2010).…”

A Literature Review of Non-Contact Tools and Methods in Structural Health Monitoring

“…Another study by Park et al [99] similarly employed additional algorithms to improve non-contact tomography methods. Difference Hilbert Back Projection (DHB) algorithm was implemented to improve the tomography imaging accuracy of plate structures imperfections.…”