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Applied Sciences
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Structural Monitoring Using Advanced NDT Techniques
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Structural Monitoring Using Advanced NDT Techniques

A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Materials Science and Engineering".

Deadline for manuscript submissions: closed (30 June 2022) | Viewed by 10191

Special Issue Editors

Prof. Dr. Il-Bum Kwon

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Guest Editor
Center for Safety Measurement, Korea Research Institute of Standards and Science (KRISS), Yuseong-gu, Daejeon 34114, Republic of Korea
Interests: fiber optic distributed sensors; structural health monitoring; impact damage detection of composites using fiber optic BOCDA sensors; physical sensing with metal-coated fibers; FBG sensors for multiplexed sensing; Fabry–Perot sensors for medical applications
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Yi-Qing Ni

E-Mail Website
Guest Editor
Hong Kong Branch of National Rail Transit Electrification and Automation Engineering Technology Research Center, Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Kowloon, Hong Kong
Interests: structural health monitoring; structural dynamics and control; smart materials and structures; sensors and actuators; bayesian inference and machine learning; high-speed rail and maglev safety
Special Issues, Collections and Topics in MDPI journals
Dr. Donghoon Kang

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Guest Editor
Railroad Safety Research Team, Korea Railroad Research Institute (KRRI), Uiwang, Gyeonggi-do 16105, Republic of Korea
Interests: nondestructive testing and evaluation skills; field application using structural health monitoring techniques; development of fiber optic sensors and field applications; convergence with internet of things technology
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Dae-Hyun Kim

E-Mail Website
Guest Editor
Department of Mechanical and Automotive Engineering, Seoul National University of Science and Technology (SeoulTech), Seoul 01811, Republic of Korea
Interests: fiber optic sensors; structural health monitoring; damage assessment with AI (deep learning) and IoT; physical sensing with FBG; composites; NDT/E
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Advanced NDT (nondestructive testing) techniques are excellent tools in order to safely maintain structures such as bridges, tunnels, and buildings, as well as cars, airplanes, ships, etc. Over the course of several decades, NDT techniques were developed to be more precise and automatic than conventional techniques, which are based on human experience. Laser ultrasonics is one such technique, which has fast defect imaging performance for plate-like materials. Machine vision is also developing well to detect some flaws in structures and materials. This vision technique is now converged with artificial intelligence and big data to clarify some targets from objects quickly and automatically. Advanced NDT techniques can involve many methods, such as holography, shearography, speckle photography, ESPI, etc. These techniques are now being developed for application in the evaluation of materials and structural status. Many advanced sensors have also been investigated for implementing real-time structural monitoring, such as wireless sensor networks, fiber optic sensors, etc. Fiber optic sensors are powerful tools for structural monitoring. FBG sensors are successfully deployed in many fields. However, these sensors are carefully prepared to be used properly for various needs.  Distributed fiber optic sensors can sense strain, temperature, vibration, and acoustics through one sensing optical fiber line. At present, the spatial resolution of these sensors is accomplished at a sub-centimeter range, which can be used to detect cracks on materials. This Special Issue of Applied Science, "Structural Monitoring Using Advanced NDT techniques", will provide recent achievements in structural monitoring and materials characterization using advanced NDT techniques. In addition, this Issue will include some papers presented in WCNDT (World Conference on Non-Destructive-testing) 2020. Your contribution is welcome and much appreciated as an author or a reviewer.

Prof. Dr. Il-Bum Kwon
Prof. Dr. Yi-qing Ni
Prof. Dr. Donghoon Kang
Prof. Dr. Dae-Hyun Kim
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Applied Sciences is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • structural health monitoring
  • wireless sensor networks
  • fiber optic sensors, distributed fiber optic sensors
  • vision systems, machine vision
  • holography, shearography
  • speckle photography, ESPI
  • composite materials
  • concrete and steel materials
  • damage detection
  • structural safety management
  • materials evaluation
  • strain, temperature, tilting, and vibration measurement
  • acoustic sensing

Published Papers (5 papers)

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Research

12 pages, 4347 KiB  
Article
Application of the Proposed Fiber Optic Time Differential BOCDA Sensor System for Impact Damage Detection of a Composite Cylinder
by Bo-Hun Choi, Dae-Cheol Seo, Yong-Seok Kwon and Il-Bum Kwon
Appl. Sci. 2021, 11(21), 10247; https://doi.org/10.3390/app112110247 - 01 Nov 2021
Cited by 5 | Viewed by 1330
Abstract
An optical-fiber-embedded composite cylinder was fabricated using the filament winding process with an interval of 12 mm in the longitudinal direction of the cylinder. The optical fiber was wound 160 turns around the cylinder, and the straight length was about 125 m. After [...] Read more.
An optical-fiber-embedded composite cylinder was fabricated using the filament winding process with an interval of 12 mm in the longitudinal direction of the cylinder. The optical fiber was wound 160 turns around the cylinder, and the straight length was about 125 m. After a total of twelve impact events of 5, 10, 15, and 20 J, the residual strain in the cylinder was measured using the proposed time differential BOCDA sensor system. This method makes the traditionally used optical delay unnecessary while increasing the degrees of freedom of using the modulation rate, which determines the spatial resolution of this measurement system. The modulation rates of optical light in the system were applied up to 16 Gbps, which is an eight-fold increase compared to our previous experiments. Damage maps were obtained by mapping the measured residual strain onto the structure of the cylinder, and compared using three spatial resolutions of 20, 10, and 6.25 mm. In the measured damage map, expansion deformation due to impact was measured at all impact points, and the impact location on the map and the actual location on the cylinder were exactly the same. The map measured from the composite showed a clear point-symmetrical shape with an increase in sharpness as the measurement resolution increased. At the highest resolution, material expansion and compression were observed to alternate with respect to the center of impact, like the surface deformation of a liquid caused by a thrown object. Furthermore, considered together with our previous experiments, we confirmed that this phenomenon propagated from the surface of the composite material to the interior, where the optical fiber was embedded. The total amount of residual strain formed around each impact point was linearly proportional to the applied external impact energy. Full article
(This article belongs to the Special Issue Structural Monitoring Using Advanced NDT Techniques)
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10 pages, 2840 KiB  
Article
High-Speed Time- and Frequency-Domain Terahertz Tomography of Glass-Fiber-Reinforced Polymer Laminates with Internal Defects
by Ji-Sang Yahng and Dae-Su Yee
Appl. Sci. 2021, 11(11), 4933; https://doi.org/10.3390/app11114933 - 27 May 2021
Cited by 2 | Viewed by 1710
Abstract
Composite materials are increasingly being utilized in many products, such as aircrafts, wind blades, etc. Accordingly, the need for nondestructive inspection of composite materials is increasing and technologies that allow nondestructive inspection are being studied. Existing ultrasound methods are limited in their ability [...] Read more.
Composite materials are increasingly being utilized in many products, such as aircrafts, wind blades, etc. Accordingly, the need for nondestructive inspection of composite materials is increasing and technologies that allow nondestructive inspection are being studied. Existing ultrasound methods are limited in their ability to detect defects due to high attenuation in composite materials, and radiographic examination methods could pose a danger to human health. Terahertz (THz) wave technology is an emerging approach that is useful for imaging of concealed objects or internal structures due to high transmittance in non-conductive materials, straightness, and safety to human health. Using high-speed THz tomography systems that we developed, we have obtained THz tomographic images of glass-fiber-reinforced polymer (GFRP) laminates with artificial internal defects such as delamination and inclusion. The defects have various thicknesses and sizes, and lie at different depths. We present THz tomographic images of GFRP samples to demonstrate the extent to which the defects can be detected with the THz tomography systems. Full article
(This article belongs to the Special Issue Structural Monitoring Using Advanced NDT Techniques)
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10 pages, 5946 KiB  
Article
A Technic for Ground Anchor Force Determination from Distributied Strain Using Fiber Optic OFDR Sensor with the Rejection of a Temperature Effect
by Il-Bum Kwon, Yong-Seok Kwon, Dae-Cheol Seo, Dong-Jin Yoon and Eunho Kim
Appl. Sci. 2020, 10(23), 8437; https://doi.org/10.3390/app10238437 - 26 Nov 2020
Cited by 4 | Viewed by 1923
Abstract
Anchor systems are widely used to stabilize soil slope and suppress slope failure. Thus, monitoring conditions of an anchor system is important to prevent disasters due to slope failure. The slope condition can be indirectly monitored by sensing the tensile force applied to [...] Read more.
Anchor systems are widely used to stabilize soil slope and suppress slope failure. Thus, monitoring conditions of an anchor system is important to prevent disasters due to slope failure. The slope condition can be indirectly monitored by sensing the tensile force applied to the anchor because the slope deformation directly affects the anchor force. Previously, we propose a way to monitor the tensile force of the anchor by measuring the strain field on a bearing plate using a distributed fiber optic sensor (OFDR) and experimentally demonstrate that the anchor force has a large correlation with the strain distribution on the bearing plate. However, it was found that a spatial variation of the strain and thermal strain due to temperature change makes it difficult to get a reliable correlation coefficient. In this study, we newly propose a way to get a reliable correlation coefficient between the anchor force and the strain field on the bearing plate. We install a distributed optical fiber sensor in two concentric circles on the bearing plate and measure circumferential strain distribution. We take average values of the strain field in each circle as representative strain values minimizing the spatial variation and takes a difference of the two strains to exclude the temperature effect. We experimentally demonstrate that the proposed method gives a reliable correlation coefficient between the anchor force and the strain field on the bearing plate. This technique can be applied to various anchor systems to monitor the anchor force and manage the anchor systems safely. Full article
(This article belongs to the Special Issue Structural Monitoring Using Advanced NDT Techniques)
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14 pages, 4926 KiB  
Article
Remaining Useful Strength (RUS) Prediction of SiCf-SiCm Composite Materials Using Deep Learning and Acoustic Emission
by Steph-Yves M. Louis, Alireza Nasiri, Jingjing Bao, Yuxin Cui, Yong Zhao, Jing Jin, Xinyu Huang and Jianjun Hu
Appl. Sci. 2020, 10(8), 2680; https://doi.org/10.3390/app10082680 - 13 Apr 2020
Cited by 6 | Viewed by 2402
Abstract
Prognosis techniques for prediction of remaining useful life (RUL) are of crucial importance to the management of complex systems for they can lead to appropriate maintenance interventions and improvements in reliability. While various data-driven methods have been introduced to predict the remaining useful [...] Read more.
Prognosis techniques for prediction of remaining useful life (RUL) are of crucial importance to the management of complex systems for they can lead to appropriate maintenance interventions and improvements in reliability. While various data-driven methods have been introduced to predict the remaining useful life (RUL) of machinery systems or batteries, no research has been reported on the remaining useful strength (RUS) prediction of silicon carbide fiber reinforced silicon carbide matrix (SiCf-SiCm) materials with pivotal role in its potential usage as a structural material in nuclear reactors and turbine engines. Knowledge of its degradation process is of the utmost importance to the manufacturers. For this purpose, two approaches based on the machine-learning techniques of random-forest (RF) and convolutional neural network (CNN) are proposed to predict the RUS of SiCf-SiCm using only acoustic emission (AE) signals generated during the material’s stress applying process. Experimental results show that the CNN models achieved better predictive performance than the RF models but the latter with expert-engineered features achieves better prediction for AE signals in the early stage of degradation. Additionally, our results demonstrate that both models can correctly predict the SiCf-SiCm RUS as evaluated by our robust testing method from which the best average root mean square error (RMSE) and Pearson correlation coefficient of 3.55 ksi units and 0.85 were obtained. Full article
(This article belongs to the Special Issue Structural Monitoring Using Advanced NDT Techniques)
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17 pages, 5130 KiB  
Article
Monitoring of Grouting Compactness in Tendon Duct Using Multi-Sensing Electro-Mechanical Impedance Method
by Bin Guo, Dongdong Chen, Linsheng Huo and Gangbing Song
Appl. Sci. 2020, 10(6), 2018; https://doi.org/10.3390/app10062018 - 16 Mar 2020
Cited by 9 | Viewed by 2032
Abstract
The structural integrity of post-tensioning prestressed concrete structures with tendon ducts highly depends on the grouting quality in construction. This paper proposes a real-time approach to monitoring the grouting compactness in tendon ducts using the multi-sensing electro-mechanical impedance (EMI) method. When Lead Zirconate [...] Read more.
The structural integrity of post-tensioning prestressed concrete structures with tendon ducts highly depends on the grouting quality in construction. This paper proposes a real-time approach to monitoring the grouting compactness in tendon ducts using the multi-sensing electro-mechanical impedance (EMI) method. When Lead Zirconate Titanate (PZT) transducers with different pre-selected dimensions are serially connected and mounted on a structure at distributed locations, each PZT provides unique resonance frequency coupled with the local structural physical property. Therefore, the impedance with multiple peaks of the serially connected multiple PZTs can be captured during a single measurement, which significantly simplifies the measurement procedure and reduces the data processing time. In addition, the wiring for the PZT sensors is also simplified. In this research, the feasibility of the proposed method was experimentally and numerically investigated to monitor the grouting compactness in a tendon duct specimen. The 3-dB mean absolute percentage deviation (MAPD) was applied to quantify the variations of the impedance signatures measured from five different grouting levels. Both experimental and numerical results verify the feasibility of using the proposed method for monitoring the grouting compactness in tendon ducts. Full article
(This article belongs to the Special Issue Structural Monitoring Using Advanced NDT Techniques)
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