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Damage Detection of Structures Based on Piezoelectric Sensors

A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Physical Sensors".

Deadline for manuscript submissions: closed (30 November 2020) | Viewed by 39713

Special Issue Editor


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Guest Editor
Reinforced Concrete Lab., Department of Civil Engineering, Structural Engineering Division, Democritus University of Thrace, University Campus, Kimmeria, 67100 Xanthi, Greece
Interests: reinforced concrete structures; seismic design of reinforced structures; damage detection of structures based on piezoelectric sensors; seismic pathology of reinforced concrete structures; rehabilitation (repair-strengthening) of structures; pre-stressed concrete
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Special Issue Information

Dear Colleague,

Structural Health Monitoring (SHM) along with damage detection and assessment of damage severity level in non-accessible structural members of existing constructions using piezoelectric materials is becoming essential, since engineers often face the problem of detecting hidden damage. The immediate and continuous nature of the acquired information flow supplied by these materials enables real-time monitoring, direct control, and rapid intervention, thus permitting to avoid structural failures or even major disasters if damage occurs in crucial installations.

It has to be stressed that the detection of damage, the assessment of its severity level in non-accessible structural members, and, even more, the on-line diagnosis and assessment of the its possible evolution in time could probably be investigated on the basis of the properties of the piezoelectric material lead ZirconateTitanate (PZT).

These challenging fields of study have already become a special area of earthquake engineering research in reinforced concrete and steel structures that are rapidly developing. Research in these areas can become essential in the near future, since engineers in seismic-prone regions often face the problem of detecting hidden damage in non-accessible structural members and, moreover, have to design appropriate interventions.

Piezoelectric sensors can produce electrical charges when subjected to a strain field and, conversely, mechanical strain when subjected to an electrical field. The recent developments in “smart” piezoelectric materials have inspired researchers to establish new non-destructive evaluation and SHM methods. New sensors and PZT-based techniques have been implemented to obtain flexible, cost-effective, robust, wireless, and mobile software/hardware solutions.

This Special Issue seeks innovative work exploring new analytical methods and experimental techniques for the non-destructive evaluation and monitoring of structural members based on the properties of the piezoelectric sensors.

Prof. Dr. Chris Karayannis
Guest Editor

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Keywords

The particular topics of interest include, but are not limited to: 
  • Piezoelectric sensors for damage detection of structures 
  • Experimental testing for damage detection, identification, and assessment using piezoelectric sensors 
  • Structural Health Monitoring (SHM) of structures using PZTs 
  • Cracking diagnosis of reinforced concrete structural members 
  • Yielding detection and corrosion evaluation of structural steel and steel reinforcement
  • Real-time, continuous, and wireless monitoring of structures 
  • Finite-element modeling 
  • Electro-Mechanical Admittance (EMA) or Impedance (EMI) techniques for SHM 
  • New sensors and techniques for SHM applications 
  • Applications and development of PZT-based non-destructive techniques

Published Papers (12 papers)

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Research

25 pages, 11129 KiB  
Article
Flexural Damage Diagnosis in Reinforced Concrete Beams Using a Wireless Admittance Monitoring System—Tests and Finite Element Analysis
by Constantin E. Chalioris, Violetta K. Kytinou, Maristella E. Voutetaki and Chris G. Karayannis
Sensors 2021, 21(3), 679; https://doi.org/10.3390/s21030679 - 20 Jan 2021
Cited by 58 | Viewed by 5346
Abstract
The utilization and effectiveness of a custom-made, portable and low-cost structural health monitoring (SHM) system that implements the PZT-based electro-mechanical admittance (EMA) methodology for the detection and evaluation of the damage of flexural reinforced concrete (RC) beams is presented. Tests of large-scale beams [...] Read more.
The utilization and effectiveness of a custom-made, portable and low-cost structural health monitoring (SHM) system that implements the PZT-based electro-mechanical admittance (EMA) methodology for the detection and evaluation of the damage of flexural reinforced concrete (RC) beams is presented. Tests of large-scale beams under monotonic and cyclic reversal-imposed deformations have been carried out using an integrated wireless impedance/admittance monitoring system (WiAMS) that employs the voltage measurements of PZT transducers. Small-sized PZT patches that have been epoxy-bonded on the steel bars surface and on the external concrete face of the beams are utilized to diagnose damages caused by steel yielding and concrete cracking. Excitations and simultaneous measurements of the voltage signal responses of the PZT transducers have been carried out at different levels of the applied load during the tests using the developed SHM devices, which are remotely controlled by a terminal emulator. Each PZT output voltage versus frequency response is transferred wireless and in real-time. Statistical index values are calculated based on the signals of the PZT transducers to represent the differences between their baseline response at the healthy state of the beam and their response at each loading/damage level. Finite Element Modeling (FEM) simulation of the tested beams has also been performed to acquire numerical results concerning the internal cracks, the steel strains and the energy dissipation and instability parameters. FEM analyses are used to verify the experimental results and to support the visual observations for a more precise damage evaluation. Findings of this study indicate that the proposed SHM system with the implementation of two different PZT transducer settings can be effectively utilized for the assessment of structural damage caused by concrete cracking and steel yielding in flexural beams under monotonic and cyclic loading. Full article
(This article belongs to the Special Issue Damage Detection of Structures Based on Piezoelectric Sensors)
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19 pages, 15009 KiB  
Article
Piezoelectric Transducer-Based Diagnostic System for Composite Structure Health Monitoring
by Egidijus Dragašius, Darius Eidukynas, Vytautas Jūrėnas, Darius Mažeika, Mantas Galdikas, Arkadiusz Mystkowski and Joanna Mystkowska
Sensors 2021, 21(1), 253; https://doi.org/10.3390/s21010253 - 2 Jan 2021
Cited by 6 | Viewed by 2435
Abstract
This paper focuses on the investigation of the diagnostic system for health monitoring and defects, detecting in composite structures using a piezoelectric sensor. A major overview of structural defects in composite materials that have an influence on product performance as well as material [...] Read more.
This paper focuses on the investigation of the diagnostic system for health monitoring and defects, detecting in composite structures using a piezoelectric sensor. A major overview of structural defects in composite materials that have an influence on product performance as well as material strength is presented. Particularly, the proposed diagnostic (health monitoring) system enables to monitor the composite material plate defects during the exploitation in real-time. The investigated health monitoring system can indicate the material structure defects when the periodic test input signal is provided to excite the plate. Especially, the diagnostic system is useful when the defect placement is hard to be identified. In this work, several various numerical and experimental studies were carried out. Particularly, during the first study, the piezoelectric transducer was used to produce mechanical excitation to the composite plate when the impact response is measured with another piezoelectric sensor. The second study focuses on the defect identification algorithms of the raw hologram data consisting of the recorded oscillation modes of the affected composite plate. The main paper results obtained in both studies enable us to determine whether the composite material is characterized by mechanical defects occurring during the response to the periodic excitation. In case of damage, the observed response amplitude was decreased by 70%. Finally, using the time-domain experimental results, the frequency response functions (FRFs) are applied to damage detection assessment and to obtain extra damage information. Full article
(This article belongs to the Special Issue Damage Detection of Structures Based on Piezoelectric Sensors)
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26 pages, 7938 KiB  
Article
Developing a Multi-Element Sensor to Non-Destructively Monitor Several Fundamental Parameters Related to Concrete Durability
by Ming Jin, Yuefeng Ma, Haoyu Zeng, Jiaping Liu, Linhua Jiang, Guo Yang and Yue Gu
Sensors 2020, 20(19), 5607; https://doi.org/10.3390/s20195607 - 30 Sep 2020
Cited by 9 | Viewed by 2013
Abstract
A design scheme of multi-element sensor which included electrical resistivity probes, multiple Cl selective electrodes, and a steel corrosion monitoring system was proposed in this work. Embedding this multi-element sensor in concrete enables the real-time and non-destructive monitoring of internal electrical resistivity, [...] Read more.
A design scheme of multi-element sensor which included electrical resistivity probes, multiple Cl selective electrodes, and a steel corrosion monitoring system was proposed in this work. Embedding this multi-element sensor in concrete enables the real-time and non-destructive monitoring of internal electrical resistivity, free Cl (Clf) contents in the concrete pore solution at different depths, and steel corrosion parameters. Based on the monitoring data obtained by the multi-element sensor, the freezing-thawing (F-T) damage degree, the Clf diffusion coefficient, the quantitative relation between F-T damage degree and Clf diffusion coefficient, the initiation period of steel corrosion, and the critical content related to steel corrosion are determined. To conclude, the multi-element sensor provides key durability parameters for the establishment of the Clf diffusion model, the assessment of health condition, and the prediction of service life of concrete under the coexistence of the F-T cycle and Cl. Full article
(This article belongs to the Special Issue Damage Detection of Structures Based on Piezoelectric Sensors)
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17 pages, 4194 KiB  
Article
Natural Frequency Response Evaluation for RC Beams Affected by Steel Corrosion Using Acceleration Sensors
by Yuwei Zhang, Yongchun Cheng, Guojin Tan, Xiang Lyu, Xun Sun, Yunshuo Bai and Shuting Yang
Sensors 2020, 20(18), 5335; https://doi.org/10.3390/s20185335 - 17 Sep 2020
Cited by 4 | Viewed by 2487
Abstract
This paper presented a laboratory investigation for analyzing the natural frequency response of reinforced concrete (RC) beams affected by steel corrosion. The electrochemical acceleration technique induced the corroded RC beams until the predetermined value of the steel corrosion ratio was achieved. Then, the [...] Read more.
This paper presented a laboratory investigation for analyzing the natural frequency response of reinforced concrete (RC) beams affected by steel corrosion. The electrochemical acceleration technique induced the corroded RC beams until the predetermined value of the steel corrosion ratio was achieved. Then, the natural frequency responses of the corroded beams were tested utilizing piezoelectric acceleration sensors. The damage states of the corroded beams were assessed through the measurement of crack parameters and the equivalent elastic modulus of the beams, which aims to clarify the fundamental characteristics of the dynamic response for the corroded RC beam with the increased steel corrosion ratio. The results revealed that steel corrosion reduces the bending stiffness of the RC beams and, thus, reduces the modal frequency. The variation of natural frequency can identify the corrosion damage even if no surface cracking of the RC beam, and the second-order frequency should be more indicative of the damage scenario. The degradations of stiffness and the natural frequency were estimated in this study by the free vibration equation of a simply supported beam, and a prediction method for the RC beam’s residual service life was established. This study supports the use of variations in natural frequency as one diagnostic indicator to evaluate the health of RC bridge structures. Full article
(This article belongs to the Special Issue Damage Detection of Structures Based on Piezoelectric Sensors)
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16 pages, 3336 KiB  
Article
Steel Corrosion Evaluation of Basalt Fiber RPC Affected by Crack and Steel-Concrete Interface Damage Using Electrochemical Methods
by Hanbing Liu, Xiang Lyu, Yuwei Zhang, Guobao Luo and Wenjun Li
Sensors 2020, 20(18), 5027; https://doi.org/10.3390/s20185027 - 4 Sep 2020
Cited by 7 | Viewed by 2240
Abstract
Basalt fiber (BF) is a new anti-corrosion and environmentally friendly material, which is expected to delay the corrosion process of steel bars and improve the durability of reinforced reactive powder concrete (RPC). The electrochemical method is a nondestructive testing and real-time monitoring technique [...] Read more.
Basalt fiber (BF) is a new anti-corrosion and environmentally friendly material, which is expected to delay the corrosion process of steel bars and improve the durability of reinforced reactive powder concrete (RPC). The electrochemical method is a nondestructive testing and real-time monitoring technique used to characterize the corrosion behaviors of steel bars embedded in concrete structures. In this paper, the electrochemical technique was employed to evaluate the corrosion of steel bars embedded in basalt fiber modified reactive powder concrete (BFRPC). Besides, crack and steel-concrete interface damage (SCID) were considered as typical factors that affect steel corrosion in concrete. Thus, both reinforced fiber-free RPC and BFRPC specimens with crack and SCID were prepared for evaluating the steel corrosion behaviors by electrochemical methods. The results revealed that both crack and SCID would aggravate the steel corrosion, and the crack was the major factor that affects the corrosion process. Moreover, the excellent compactness of BFRPC and the bridging action of BF could effectively prevent the concrete cracking and steel corrosion process of concrete. Using reinforced BFRPC instead of ordinary concrete in practical projects could greatly extend the service life of steel bars. Full article
(This article belongs to the Special Issue Damage Detection of Structures Based on Piezoelectric Sensors)
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21 pages, 7416 KiB  
Article
Experimental Study on Damage Identification of Nano-SiO2 Concrete Filled GFRP Tube Column Using Piezoceramic Transducers
by Xixiang Chen and Yu Chen
Sensors 2020, 20(10), 2883; https://doi.org/10.3390/s20102883 - 19 May 2020
Cited by 5 | Viewed by 2037
Abstract
This paper proposes a new approach to damage detection of nano-SiO2 concrete-filled glass fiber reinforced polymer (GFRP) tube column using piezoceramic transducers. Stress waves are emitted and received by a pair of piezoceramic transducers embedded in the concrete-filled GFRP tube, and the [...] Read more.
This paper proposes a new approach to damage detection of nano-SiO2 concrete-filled glass fiber reinforced polymer (GFRP) tube column using piezoceramic transducers. Stress waves are emitted and received by a pair of piezoceramic transducers embedded in the concrete-filled GFRP tube, and the energy and damage indices at different levels of loading in the tube are obtained by wavelet packet to evaluate the damage degree of GFRP tube nano-SiO2 concrete column. Through the experimental studies, the effects of different nano-SiO2 contents, concrete grades, and superplasticizer on the damage were analyzed to gain load–displacement curves, load–energy index curves, and load–damage index curves. The results show that the wave method can be adopted to monitor the damage of GFRP tube nano-SiO2 concrete column. The specimens with 3% nano-SiO2 content have the smallest energy change rate, indicating that adding 3% nano-SiO2 content into concrete can effectively delay the development of damage. After the addition of superplasticizer, with the increase in the strength grade of concrete, the cracks in the specimen tend to develop slowly, and therefore the specimens have a stronger resistance to damage. The damage of the specimens with the nano-SiO2 content of 1% appeared the latest, while the damage without the nano-SiO2 specimen appeared the fastest. The experimental results show that this method can better monitor the damage of the Nano-SiO2 concrete in the glass fiber reinforced polymer (GFRP) tube. Full article
(This article belongs to the Special Issue Damage Detection of Structures Based on Piezoelectric Sensors)
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18 pages, 6617 KiB  
Article
Piezoceramic-Based Damage Monitoring of Concrete Structure for Underwater Blasting
by Jianfeng Si, Dongwang Zhong and Wei Xiong
Sensors 2020, 20(6), 1672; https://doi.org/10.3390/s20061672 - 17 Mar 2020
Cited by 4 | Viewed by 6335
Abstract
This paper developed a piezoelectric-transducer-based damage detection of concrete materials after blasting. Two specimens (with or without an energy-relieving structure) were subjected to a 40 m deep-underwater blasting load in an underwater-explosion vessel, and their damage was detected by a multifunctional piezoelectric-signal-monitoring and [...] Read more.
This paper developed a piezoelectric-transducer-based damage detection of concrete materials after blasting. Two specimens (with or without an energy-relieving structure) were subjected to a 40 m deep-underwater blasting load in an underwater-explosion vessel, and their damage was detected by a multifunctional piezoelectric-signal-monitoring and -analysis system before and after the explosion. Statistical-data analysis of the piezoelectric signals revealed four zones: crushing, fracture, damage, and safe zones. The signal energy was analyzed and calculated by wavelet-packet analysis, and the blasting-damage index was obtained after the concrete specimen was subjected to the impact load of the underwater explosion. The damage of the two specimens gradually decreased from the blast hole to the bottom of the specimen. The damage index of the specimen with the energy-relieving structure differed for the fracture area and the damage area, and the damage protection of the energy-relieving structure was prominent at the bottom of the specimen. The piezoelectric-transducer-based damage monitoring of concrete materials is sensitive to underwater blasting, and with wavelet-packet-energy analysis, it can be used for postblasting damage detection and the evaluation of concrete materials. Full article
(This article belongs to the Special Issue Damage Detection of Structures Based on Piezoelectric Sensors)
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18 pages, 5985 KiB  
Article
Detecting of the Longitudinal Grouting Quality in Prestressed Curved Tendon Duct Using Piezoceramic Transducers
by Tianyong Jiang, Bin He, Yaowen Zhang and Lei Wang
Sensors 2020, 20(4), 1212; https://doi.org/10.3390/s20041212 - 22 Feb 2020
Cited by 12 | Viewed by 3000
Abstract
To understand the characteristics of longitudinal grouting quality, this paper developed a stress wave-based active sensing method using piezoceramic transducers to detect longitudinal grouting quality of the prestressed curved tendon ducts. There were four lead zirconate titanate (PZT) transducers installed in the same [...] Read more.
To understand the characteristics of longitudinal grouting quality, this paper developed a stress wave-based active sensing method using piezoceramic transducers to detect longitudinal grouting quality of the prestressed curved tendon ducts. There were four lead zirconate titanate (PZT) transducers installed in the same longitudinal plane. One of them, mounted on the bottom of the curved tendon duct, was called as an actuator for generating stress waves. The other three, pasted on the top of the curved tendon duct, were called as sensors for detecting the wave responses. The experimental process was divided into five states during the grouting, which included 0%, 50%, 75%, 90%, and 100% grouting. The voltage signals, power spectral density (PSD) energy and wavelet packet energy were adopted in this research. Experimental results showed that all the amplitudes of the above analysis indicators were small before the grouting reached 90%. Only when the grouting degree reached the 100% grouting, these parameters increased significantly. The results of different longitudinal PZT sensors were mainly determined by the distance from the generator, the position of grouting holes, and the fluidity of grouting materials. These results showed the longitudinal grouting quality can be effectively evaluated by analyzing the difference between the signals received by the PZT transducers in the curved tendon duct. The devised method has certain application value in detecting the longitudinal grouting quality of prestressed curved tendon duct. Full article
(This article belongs to the Special Issue Damage Detection of Structures Based on Piezoelectric Sensors)
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20 pages, 5333 KiB  
Article
Sensor Fault Diagnosis for Impedance Monitoring Using a Piezoelectric-Based Smart Interface Technique
by Thanh-Canh Huynh, The-Duong Nguyen, Duc-Duy Ho, Ngoc-Loi Dang and Jeong-Tae Kim
Sensors 2020, 20(2), 510; https://doi.org/10.3390/s20020510 - 16 Jan 2020
Cited by 31 | Viewed by 3588
Abstract
For a structural health monitoring (SHM) system, the operational functionality of sensors is critical for successful implementation of a damage identification process. This study presents experimental and analytical investigations on sensor fault diagnosis for impedance-based SHM using the piezoelectric interface technique. Firstly, the [...] Read more.
For a structural health monitoring (SHM) system, the operational functionality of sensors is critical for successful implementation of a damage identification process. This study presents experimental and analytical investigations on sensor fault diagnosis for impedance-based SHM using the piezoelectric interface technique. Firstly, the piezoelectric interface-based impedance monitoring is experimentally conducted on a steel bolted connection to investigate the effect of structural damage and sensor defect on electromechanical (EM) impedance responses. Based on the experimental analysis, sensor diagnostic approaches using EM impedance features are designed to distinguish the sensor defect from the structural damage. Next, a novel impedance model of the piezoelectric interface-driven system is proposed for the analytical investigation of sensor fault diagnosis. Various parameters are introduced into the EM impedance formulation to model the effect of shear-lag phenomenon, sensor breakage, sensor debonding, and structural damage. Finally, the proposed impedance model is used to analytically estimate the change in EM impedance responses induced by the structural damage and the sensor defect. The analytical results are found to be consistent with experimental observations, thus evidencing the feasibility of the novel impedance model for sensor diagnosis and structural integrity assessment. The study is expected to provide theoretical and experimental foundations for impedance monitoring practices, using the piezoelectric interface technique, with the existence of sensor faults. Full article
(This article belongs to the Special Issue Damage Detection of Structures Based on Piezoelectric Sensors)
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18 pages, 4999 KiB  
Article
Circumferential SH Wave Piezoelectric Transducer System for Monitoring Corrosion-Like Defect in Large-Diameter Pipes
by Hao Zhang, Yuehao Du, Jihua Tang, Guozheng Kang and Hongchen Miao
Sensors 2020, 20(2), 460; https://doi.org/10.3390/s20020460 - 14 Jan 2020
Cited by 23 | Viewed by 3707
Abstract
The fundamental circumferential shear horizontal (CSH0) wave is of practical importance in monitoring corrosion defects in large-diameter pipes due to its virtually non-dispersive characteristics. However, so far, there have been limited CSH0 wave transducers which can be used to constitute [...] Read more.
The fundamental circumferential shear horizontal (CSH0) wave is of practical importance in monitoring corrosion defects in large-diameter pipes due to its virtually non-dispersive characteristics. However, so far, there have been limited CSH0 wave transducers which can be used to constitute a structural health monitoring (SHM) system for pipes. Moreover, the CSH0 wave’s capability of sizing the corrosion-like defect has not yet been confirmed by experiments. In this work, firstly, the mechanism of exciting CSH waves was analyzed. A method based on our previously developed bidirectional SH wave piezoelectric transducers was then proposed to excite the pure CSH0 mode and first order circumferential shear horizontal (CSH1) mode. Both finite element simulations and experiments show that the bidirectional transducer is capable of exciting pure CSH0 mode traveling in both circumferential directions of a 1-mm thick steel pipe from 100 to 300 kHz. Moreover, this transducer can also serve a sensor to detect CSH0 mode only by filtering circumferential Lamb waves over a wide frequency range from 100 to 450 kHz. After that, a method of sizing a rectangular notch defect by using CSH0 wave was proposed. Experiments on an 11-mm thick steel pipe show that the depth and circumferential extent of a notch can be accurately determined by using the proposed method. Finally, experiments were performed to investigate the reflection and transmission characteristics of CSH0 and CSH1 waves from notches with different depths. It was found that transmission coefficients of CSH0 mode decrease with the increasing of notch depth, which indicates that it is possible to monitor the depth change of corrosion defects by using CSH0 wave. Full article
(This article belongs to the Special Issue Damage Detection of Structures Based on Piezoelectric Sensors)
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23 pages, 6005 KiB  
Article
An EMI-Based Clustering for Structural Health Monitoring of NSM FRP Strengthening Systems
by Ricardo Perera, Lluis Torres, Antonio Ruiz, Cristina Barris and Marta Baena
Sensors 2019, 19(17), 3775; https://doi.org/10.3390/s19173775 - 31 Aug 2019
Cited by 38 | Viewed by 2745
Abstract
The use of fiber-reinforced polymers (FRP) in civil construction applications with the near-surface mounted (NSM) method has gained considerable popularity worldwide and can produce confident strengthening and repairing systems for existing concrete structures. By using this technique, the FRP reinforcement is installed into [...] Read more.
The use of fiber-reinforced polymers (FRP) in civil construction applications with the near-surface mounted (NSM) method has gained considerable popularity worldwide and can produce confident strengthening and repairing systems for existing concrete structures. By using this technique, the FRP reinforcement is installed into slits cut into the concrete cover using cement mortar or epoxy as bonding materials, yielding an attractive method to strengthen concrete structures as an advantageous alternative to the external bonding of FRP sheets. However, in addition to the two conventional failure modes of concrete beams, sudden and brittle debonding failures are still likely to happen. Due to this, a damage identification technology able to identify anomalies at early stages is needed. In this work, some relevant cluster-based methods and their adaptation to electromechanical impedance (EMI)-based damage detection in NSM-FRP strengthened structures are developed and validated with experimental tests. The performance of the proposed clustering approaches and their evaluation in comparison with the experimental observations have shown a strong potential of these techniques as damage identification methodology in an especially complex problem such as NSM-FRP strengthened concrete structures. Full article
(This article belongs to the Special Issue Damage Detection of Structures Based on Piezoelectric Sensors)
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16 pages, 4183 KiB  
Article
Wavenumber Imaging of Near-Surface Defects in Rails using Green’s Function Reconstruction of Ultrasonic Diffuse Fields
by Hui Zhang, Haiyan Zhang, Jiayan Zhang, Jianquan Liu, Wenfa Zhu, Guopeng Fan and Qi Zhu
Sensors 2019, 19(17), 3744; https://doi.org/10.3390/s19173744 - 29 Aug 2019
Cited by 6 | Viewed by 2562
Abstract
Wavenumber imaging with Green’s function reconstruction of ultrasonic diffuse fields is used to realize fast imaging of near-surface defects in rails. Ultrasonic phased array has been widely used in industries because of its high sensitivity and strong flexibility. However, the directly measured signal [...] Read more.
Wavenumber imaging with Green’s function reconstruction of ultrasonic diffuse fields is used to realize fast imaging of near-surface defects in rails. Ultrasonic phased array has been widely used in industries because of its high sensitivity and strong flexibility. However, the directly measured signal is always complicated by noise caused by physical limitations of the acquisition system. To overcome this problem, the cross-correlations of the diffuse field signals captured by the probe are performed to reconstruct the Green’s function. These reconstructed signals can restore the early time information from the noise. Experiments were conducted on rails with near-surface defects. The results confirm the effectiveness of the cross-correlation method to reconstruct the Green’s function for the detection of near-surface defects. Different kinds of ultrasonic phased array probes were applied to collect experimental data on the surface of the rails. The Green’s function recovery is related to the number of phased array elements and the excitation frequency. In addition, the duration and starting time of the time-windowed diffuse signals were explored in order to achieve high-quality defect images. Full article
(This article belongs to the Special Issue Damage Detection of Structures Based on Piezoelectric Sensors)
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