TY - JOUR A1 - Barzegar, M. A1 - Lugovtsova, Yevgeniya A1 - Bulling, Jannis A1 - Mishurova, Tatiana A1 - Pasadas, Dario J. A1 - Ribeiro, Artur L. A1 - Ramos, Helena G. T1 - Adhesive Porosity Analysis of Composite Adhesive Joints Using Ultrasonic Guided Waves N2 - Adhesively bonded composite joints can develop voids and porosity during fabrication, leading to stress concentration and a reduced load-carrying capacity. Hence, adhesive porosity analysis during the fabrication is crucial to ensure the required quality and reliability. Ultrasonic-guided wave (UGW)-based techniques without advanced signal processing often provide low-resolution imaging and can be ineffective for detecting small-size defects. This article proposes a damage imaging process for adhesive porosity analysis of bonded composite plates using UGWs measured by scanning laser Doppler vibrometer (LDV). To implement this approach, a piezoelectric transducer is mounted on the composite joint specimen to generate UGWs, which are measured over a densely sampled area. The signals obtained from the scan are processed using the proposed signal processing in different domains. Through the utilization of filter banks in frequency and wavenumber domains, along with the root-mean-square calculation of filtered signals, damage images of the adhesive region are obtained. It has been observed that different filters provide information related to different void sizes. Combining all the images reconstructed by filters, a final image is obtained which contains damages of various sizes. The images obtained by the proposed method are verified by radiography results and the porosity analysis is presented. The results indicate that the proposed methodology can detect the pores with the smallest detectable pore area of 2.41 mm^2, corresponding to a radius of 0.88 mm, with an overall tendency to overestimate the pore size by an average of 11%. KW - Adhesives KW - Damage imaging KW - Nondestructive testing (NDT) KW - Porosity analysis KW - Signal processing KW - Ultrasonic guided waves (UGWs) PY - 2024 DO - https://doi.org/10.1109/TUFFC.2024.3371671 VL - 71 IS - 4 SP - 485 EP - 495 PB - Institute of Electrical and Electronics Engineers (IEEE) AN - OPUS4-59970 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Ahmadi, Samim A1 - Kästner, L. A1 - Hauffen, Jan Christian A1 - Jung, P. A1 - Ziegler, Mathias T1 - Photothermal-SR-Net: A customized deep unfolding neural network for photothermal super resolution imaging N2 - This article presents deep unfolding neural networks to handle inverse problems in photothermal radiometry enabling super-resolution (SR) imaging. The photothermal SR approach is a well-known technique to overcome the spatial resolution limitation in photothermal imaging by extracting high-frequency spatial components based on the deconvolution with the thermal point spread function (PSF). However, stable deconvolution can only be achieved by using the sparse structure of defect patterns, which often requires tedious, handcrafted tuning of hyperparameters and results in computationally intensive algorithms. On this account, this article proposes Photothermal-SR-Net, which performs deconvolution by deep unfolding considering the underlying physics. Since defects appear sparsely in materials, our approach includes trained block-sparsity thresholding in each convolutional layer. This enables to super-resolve 2-D thermal images for nondestructive testing (NDT) with a substantially improved convergence rate compared to classic approaches. The performance of the proposed approach is evaluated on various deep unfolding and thresholding approaches. Furthermore, we explored how to increase the reconstruction quality and the computational performance. Thereby, it was found that the computing time for creating high-resolution images could be significantly reduced without decreasing the reconstruction quality by using pixel binning as a preprocessing step. KW - Deep unfolding KW - Defect reconstruction KW - Elastic net KW - Inverse problems KW - Iterative shrinkage thresholding KW - Neural network KW - Nondestructive testing (NDT) KW - Photothermal imaging KW - Super resolution (SR) KW - Thermography PY - 2022 DO - https://doi.org/10.1109/tim.2022.3154803 SN - 1557-9662 VL - 71 SP - 1 EP - 9 PB - IEEE AN - OPUS4-54678 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Shokouhi, Parisa A1 - Wolf, Julia A1 - Wiggenhauser, Herbert T1 - Detection of delamination in concrete bridge decks by joint amplitude and phase analysis of ultrasonic array measurements N2 - The accuracy and precision of low-frequency (center frequency of approximately 55 kHz) ultrasonic testing for detection and characterization of delamination in concrete bridge decks were evaluated. A multiprobe ultrasonic testing system (with horizontally polarized shear-wave transducers) was used to detect built-in delamination defects of various size, depth, and severity (i.e., thickness) in a test specimen—a 6.1 m × 2.4 m × 216 mm (20 ft × 8 ft × 8.5 in.) reinforced concrete slab-built to simulate a concrete bridge deck. The collected data sets were reconstructed applying synthetic aperture focusing technique (SAFT). The reconstructed measurement results were then used to assess the condition of the concrete slab at individual points [point-by-point data collection and two-dimensional (2D) reconstruction] as well as along lines, where data were collected at smaller steps and reconstructed in a three-dimensional (3D) format. The local-phase information was also calculated, superimposed on the reconstructed images and used as complementary information in condition assessment. The precision and accuracy of condition assessments were evaluated. The results indicated that, using the multiprobe ultrasonic array, delamination defects as small as 30 cm² (1 ft²) could be reliably detected. Deep delaminations [i.e., those deeper than 150 mm (6 in.)] were directly detected and characterized, whereas shallow delaminations [shallower than 65 mm (2.5 in.)] were detected only indirectly. The precision of the measurements was demonstrated by comparing repeated measurements at several test points. Similar measurement results obtained on a delaminated portion of a real bridge deck support the conclusions of the validation study. KW - Concrete bridge deck KW - Bridge deck evaluation KW - Delamination KW - Nondestructive testing (NDT) KW - Ultrasonic testing PY - 2014 DO - https://doi.org/10.1061/(ASCE)BE.1943-5592.0000513 SN - 1084-0702 VL - 19 IS - 3 SP - 04013005-1 EP - 04013005-11 PB - Soc. CY - Reston, Va. AN - OPUS4-31261 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Shokouhi, Parisa A1 - Zoëga, Andreas A1 - Wiggenhauser, Herbert ED - Thompson, D.O. ED - Chimenti, D.E. T1 - Nondestructive evaluation of damage in concrete under uniaxial compression N2 - Surface wave velocities over the sonic frequency range (<20 KHz) were measured on concrete specimens undergoing various cycles of loading and unloading. Acoustic Emission test (AE) was conducted simultaneously to monitor the microcracking activities. The sonic surface wave velocity was found to be highly stress-dependent. The observed changes in surface wavespeed are repeatable and follow a particular trend. By measuring the wave velocities in both loading and unloading phases, the effects of stress and stress-induced damages could be distinguished. The observed trend could be explained by a combination of acoustoelasticity and microcracking theories. T2 - 36th Annual Review of Progress in Quantitative Nondestructive Evaluation CY - Kingston, RI, USA DA - 2009-07-26 KW - Nondestructive testing (NDT) KW - Microcracking KW - Sonic wave velocity KW - Concrete KW - Load KW - Stress PY - 2010 UR - http://link.aip.org/link/?APCPCS/1211/1525/1 SN - 978-0-7354-0748-0 SN - 0743-0760 SN - 0094-243X N1 - Serientitel: AIP conference proceedings – Series title: AIP conference proceedings SP - 1525 EP - 1532 CY - Melville, NY AN - OPUS4-22642 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -