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Sensor Technologies for Health Monitoring of Composite Structures
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Sensor Technologies for Health Monitoring of Composite Structures

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

Deadline for manuscript submissions: closed (31 October 2017) | Viewed by 117921

Special Issue Editors

Prof. Dr. M. H. Ferri Aliabadi

E-Mail Website
Guest Editor
Department of Aeronautics, Faculty of Engineering, Imperial College London, London, UK
Interests: aeronautics; fracture mechanics; structural health monitoring; computational mechanics
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Zahra Sharif Khodaei

E-Mail Website
Guest Editor
Department of Aeronautics, Imperial College London, South Kensington Campus, Exhibition Road, London SW7 2AZ, UK
Interests: piezoelectric transducres for health monitoring; fibre optic sensors for strain monitoring; condition-based maintenance for composites; uncertainty quantification; reliability and risk analysis
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Advances in sensor technology have led to Structural Health Monitoring (SHM), increasingly being considered as a viable alternative to Non-Destructive Inspection (NDI), for composite materials.

The main goal of SHM is damage detection and characterization from sensor data, with a high level of reliability, in complex structures. The performance and structural integrity of the sensors (embedded/surface mounted), subjected to operational and environmental loads, are of particular interest.

This Special Issue aims to highlight advances in technology, manufacturing, and modelling of sensors and actuators for health monitoring of aerospace, civil, and marine composite structures. Topics include, but are not limited to:

  • Piezoelectric transducers,

  • Fibre Optic sensors,

  • PVDF transducers

  • Carbon Nano-Tube (CNT) based sensors

  • Graphene Nano-Pellet (GNP) based sensors

  • Wireless technology

  • Hybrid technology

  • 3D printing technology for sensors

Prof. M.H. Ferri Aliabadi
Dr. Zahra Sharif Khodaei
Guest Editors

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Keywords

  • Structural Health Monitoring

  • Composites

  • Ultrasonic Guided Waves

  • Fibre Optics

  • Damage detection

  • Uncertainty quantification

  • Reliability analysis

  • Strain sensors

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Published Papers (20 papers)

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Research

24 pages, 7606 KiB  
Article
Features of Cross-Correlation Analysis in a Data-Driven Approach for Structural Damage Assessment
by Jhonatan Camacho Navarro, Magda Ruiz, Rodolfo Villamizar, Luis Mujica and Jabid Quiroga
Sensors 2018, 18(5), 1571; https://doi.org/10.3390/s18051571 - 15 May 2018
Cited by 12 | Viewed by 4707
Abstract
This work discusses the advantage of using cross-correlation analysis in a data-driven approach based on principal component analysis (PCA) and piezodiagnostics to obtain successful diagnosis of events in structural health monitoring (SHM). In this sense, the identification of noisy data and outliers, as [...] Read more.
This work discusses the advantage of using cross-correlation analysis in a data-driven approach based on principal component analysis (PCA) and piezodiagnostics to obtain successful diagnosis of events in structural health monitoring (SHM). In this sense, the identification of noisy data and outliers, as well as the management of data cleansing stages can be facilitated through the implementation of a preprocessing stage based on cross-correlation functions. Additionally, this work evidences an improvement in damage detection when the cross-correlation is included as part of the whole damage assessment approach. The proposed methodology is validated by processing data measurements from piezoelectric devices (PZT), which are used in a piezodiagnostics approach based on PCA and baseline modeling. Thus, the influence of cross-correlation analysis used in the preprocessing stage is evaluated for damage detection by means of statistical plots and self-organizing maps. Three laboratory specimens were used as test structures in order to demonstrate the validity of the methodology: (i) a carbon steel pipe section with leak and mass damage types, (ii) an aircraft wing specimen, and (iii) a blade of a commercial aircraft turbine, where damages are specified as mass-added. As the main concluding remark, the suitability of cross-correlation features combined with a PCA-based piezodiagnostic approach in order to achieve a more robust damage assessment algorithm is verified for SHM tasks. Full article
(This article belongs to the Special Issue Sensor Technologies for Health Monitoring of Composite Structures)
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17 pages, 7624 KiB  
Article
Structural Health Monitoring of a Composite Panel Based on PZT Sensors and a Transfer Impedance Framework
by Michal Dziendzikowski, Patryk Niedbala, Artur Kurnyta, Kamil Kowalczyk and Krzysztof Dragan
Sensors 2018, 18(5), 1521; https://doi.org/10.3390/s18051521 - 11 May 2018
Cited by 37 | Viewed by 4575
Abstract
One of the ideas for development of Structural Health Monitoring (SHM) systems is based on excitation of elastic waves by a network of PZT piezoelectric transducers integrated with the structure. In the paper, a variant of the so-called Transfer Impedance (TI) approach to [...] Read more.
One of the ideas for development of Structural Health Monitoring (SHM) systems is based on excitation of elastic waves by a network of PZT piezoelectric transducers integrated with the structure. In the paper, a variant of the so-called Transfer Impedance (TI) approach to SHM is followed. Signal characteristics, called the Damage Indices (DIs), were proposed for data presentation and analysis. The idea underlying the definition of DIs was to maintain most of the information carried by the voltage induced on PZT sensors by elastic waves. In particular, the DIs proposed in the paper should be sensitive to all types of damage which can influence the amplitude or the phase of the voltage induced on the sensor. Properties of the proposed DIs were investigated experimentally using a GFRP composite panel equipped with PZT networks attached to its surface and embedded into its internal structure. Repeatability and stability of DI indications under controlled conditions were verified in tests. Also, some performance indicators for surface-attached and structure-embedded sensors were obtained. The DIs’ behavior was dependent mostly on the presence of a simulated damage in the structure. Anisotropy of mechanical properties of the specimen, geometrical properties of PZT network as well as, to some extent, the technology of sensor integration with the structure were irrelevant for damage indication. This property enables the method to be used for damage detection and classification. Full article
(This article belongs to the Special Issue Sensor Technologies for Health Monitoring of Composite Structures)
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14 pages, 3223 KiB  
Article
Plane Wave SH0 Piezoceramic Transduction Optimized Using Geometrical Parameters
by Guillaume Boivin, Martin Viens and Pierre Belanger
Sensors 2018, 18(2), 542; https://doi.org/10.3390/s18020542 - 10 Feb 2018
Cited by 9 | Viewed by 3565
Abstract
Structural health monitoring is a prominent alternative to the scheduled maintenance of safety-critical components. The nondispersive nature as well as the through-thickness mode shape of the fundamental shear horizontal guided wave mode (SH 0 ) make it a particularly attractive candidate for ultrasonic [...] Read more.
Structural health monitoring is a prominent alternative to the scheduled maintenance of safety-critical components. The nondispersive nature as well as the through-thickness mode shape of the fundamental shear horizontal guided wave mode (SH 0 ) make it a particularly attractive candidate for ultrasonic guided wave structural health monitoring. However, plane wave excitation of SH 0 at a high level of purity remains challenging because of the existence of the fundamental Lamb modes (A 0 and S 0 ) below the cutoff frequency thickness product of high-order modes. This paper presents a piezoelectric transducer concept optimized for plane SH 0 wave transduction based on the transducer geometry. The transducer parameter exploration was initially performed using a simple analytical model. A 3D multiphysics finite element model was then used to refine the transducer design. Finally, an experimental validation was conducted with a 3D laser Doppler vibrometer system. The analytical model, the finite element model, and the experimental measurement showed excellent agreement. The modal selectivity of SH 0 within a 20 ∘ beam opening angle at the design frequency of 425 kHz in a 1.59 mm aluminum plate was 23 dB, and the angle of the 6 dB wavefront was 86 ∘ . Full article
(This article belongs to the Special Issue Sensor Technologies for Health Monitoring of Composite Structures)
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13 pages, 1835 KiB  
Article
Stress Prediction for Distributed Structural Health Monitoring Using Existing Measurements and Pattern Recognition
by Wei Lu, Jun Teng, Qiushi Zhou and Qiexin Peng
Sensors 2018, 18(2), 419; https://doi.org/10.3390/s18020419 - 1 Feb 2018
Cited by 14 | Viewed by 4173
Abstract
The stress in structural steel members is the most useful and directly measurable physical quantity to evaluate the structural safety in structural health monitoring, which is also an important index to evaluate the stress distribution and force condition of structures during structural construction [...] Read more.
The stress in structural steel members is the most useful and directly measurable physical quantity to evaluate the structural safety in structural health monitoring, which is also an important index to evaluate the stress distribution and force condition of structures during structural construction and service phases. Thus, it is common to set stress as a measure in steel structural monitoring. Considering the economy and the importance of the structural members, there are only a limited number of sensors that can be placed, which means that it is impossible to obtain the stresses of all members directly using sensors. This study aims to develop a stress response prediction method for locations where there are insufficent sensors, using measurements from a limited number of sensors and pattern recognition. The detailed improved aspects are: (1) a distributed computing process is proposed, where the same pattern is recognized by several subsets of measurements; and (2) the pattern recognition using the subset of measurements is carried out by considering the optimal number of sensors and number of fusion patterns. The validity and feasibility of the proposed method are verified using two examples: the finite-element simulation of a single-layer shell-like steel structure, and the structural health monitoring of the space steel roof of Shenzhen Bay Stadium; for the latter, the anti-noise performance of this method is verified by the stress measurements from a real-world project. Full article
(This article belongs to the Special Issue Sensor Technologies for Health Monitoring of Composite Structures)
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4737 KiB  
Article
Integration of High-Resolution Laser Displacement Sensors and 3D Printing for Structural Health Monitoring
by Shu-Wei Chang, Tzu-Kang Lin, Shih-Yu Kuo and Ting-Hsuan Huang
Sensors 2018, 18(1), 19; https://doi.org/10.3390/s18010019 - 22 Dec 2017
Cited by 8 | Viewed by 5763
Abstract
This paper presents a novel experimental design for complex structural health monitoring (SHM) studies achieved by integrating 3D printing technologies, high-resolution laser displacement sensors, and multiscale entropy SHM theory. A seven-story structure with a variety of composite bracing systems was constructed using a [...] Read more.
This paper presents a novel experimental design for complex structural health monitoring (SHM) studies achieved by integrating 3D printing technologies, high-resolution laser displacement sensors, and multiscale entropy SHM theory. A seven-story structure with a variety of composite bracing systems was constructed using a dual-material 3D printer. A wireless Bluetooth vibration speaker was used to excite the ground floor of the structure, and high-resolution laser displacement sensors (1-μm resolution) were used to monitor the displacement history on different floors. Our results showed that the multiscale entropy SHM method could detect damage on the 3D-printed structures. The results of this study demonstrate that integrating 3D printing technologies and high-resolution laser displacement sensors enables the design of cheap, fast processing, complex, small-scale civil structures for future SHM studies. The novel experimental design proposed in this study provides a suitable platform for investigating the validity and sensitivity of SHM in different composite structures and damage conditions for real life applications in the future. Full article
(This article belongs to the Special Issue Sensor Technologies for Health Monitoring of Composite Structures)
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8793 KiB  
Article
Strain Gauges Based on CVD Graphene Layers and Exfoliated Graphene Nanoplatelets with Enhanced Reproducibility and Scalability for Large Quantities
by Volkan Yokaribas, Stefan Wagner, Daniel S. Schneider, Philipp Friebertshäuser, Max C. Lemme and Claus-Peter Fritzen
Sensors 2017, 17(12), 2937; https://doi.org/10.3390/s17122937 - 18 Dec 2017
Cited by 25 | Viewed by 8935
Abstract
The two-dimensional material graphene promises a broad variety of sensing activities. Based on its low weight and high versatility, the sensor density can significantly be increased on a structure, which can improve reliability and reduce fluctuation in damage detection strategies such as structural [...] Read more.
The two-dimensional material graphene promises a broad variety of sensing activities. Based on its low weight and high versatility, the sensor density can significantly be increased on a structure, which can improve reliability and reduce fluctuation in damage detection strategies such as structural health monitoring (SHM). Moreover; it initializes the basis of structure–sensor fusion towards self-sensing structures. Strain gauges are extensively used sensors in scientific and industrial applications. In this work, sensing in small strain fields (from −0.1% up to 0.1%) with regard to structural dynamics of a mechanical structure is presented with sensitivities comparable to bulk materials by measuring the inherent piezoresistive effect of graphene grown by chemical vapor deposition (CVD) with a very high aspect ratio of approximately 4.86 × 108. It is demonstrated that the increasing number of graphene layers with CVD graphene plays a key role in reproducible strain gauge application since defects of individual layers may become less important in the current path. This may lead to a more stable response and, thus, resulting in a lower scattering.. Further results demonstrate the piezoresistive effect in a network consisting of liquid exfoliated graphene nanoplatelets (GNP), which result in even higher strain sensitivity and reproducibility. A model-assisted approach provides the main parameters to find an optimum of sensitivity and reproducibility of GNP films. The fabricated GNP strain gauges show a minimal deviation in PRE effect with a GF of approximately 5.6 and predict a linear electromechanical behaviour up to 1% strain. Spray deposition is used to develop a low-cost and scalable manufacturing process for GNP strain gauges. In this context, the challenge of reproducible and reliable manufacturing and operating must be overcome. The developed sensors exhibit strain gauges by considering the significant importance of reproducible sensor performances and open the path for graphene strain gauges for potential usages in science and industry. Full article
(This article belongs to the Special Issue Sensor Technologies for Health Monitoring of Composite Structures)
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13671 KiB  
Article
Microwave Non-Destructive Inspection and Prediction of Modulus of Rupture and Modulus of Elasticity of Engineered Cementitious Composites (ECCs) Using Dual-Frequency Correlation
by Kwok L. Chung, Chunwei Zhang, Yuanyuan Li, Li Sun and Mohamed Ghannam
Sensors 2017, 17(12), 2831; https://doi.org/10.3390/s17122831 - 6 Dec 2017
Cited by 12 | Viewed by 4462
Abstract
This research article presents dual-frequency correlation models for predicting the growth of elasticity and flexural strength of engineered cementitious composites (ECCs) using microwave nondestructive inspection technique. Parallel measurements of microwave properties and mechanical properties of ECC specimens were firstly undertaken in the sense [...] Read more.
This research article presents dual-frequency correlation models for predicting the growth of elasticity and flexural strength of engineered cementitious composites (ECCs) using microwave nondestructive inspection technique. Parallel measurements of microwave properties and mechanical properties of ECC specimens were firstly undertaken in the sense of cross-disciplinary experiments. Regression models were developed via means of nonlinear regression to the measured data. The purpose of the study is: (i) to monitor the flexural strength and elasticity growth; and (ii) to predict their mature values under the influence of different initial water contents, via microwave effective conductance at early ages. It has been demonstrated that both the modulus of rupture (MOR) and modulus of elasticity (MOE) can be accurately modeled and correlated by microwave conductance using exponential functions. The moduli developed as a function of conductance whereas the regression coefficient exhibited a linear relation with water-to-binder ratio. These findings have highlighted the effectiveness of the microwave non-destructive technique in inspecting the variation of liquid phase morphology of ECCs. The dual-frequency correlation can be used for structural health monitoring, which is not only for prediction but also provides a means of verification. Full article
(This article belongs to the Special Issue Sensor Technologies for Health Monitoring of Composite Structures)
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8981 KiB  
Article
Modeling of Sensor Placement Strategy for Shape Sensing and Structural Health Monitoring of a Wing-Shaped Sandwich Panel Using Inverse Finite Element Method
by Adnan Kefal and Mehmet Yildiz
Sensors 2017, 17(12), 2775; https://doi.org/10.3390/s17122775 - 30 Nov 2017
Cited by 66 | Viewed by 8138
Abstract
This paper investigated the effect of sensor density and alignment for three-dimensional shape sensing of an airplane-wing-shaped thick panel subjected to three different loading conditions, i.e., bending, torsion, and membrane loads. For shape sensing analysis of the panel, the Inverse Finite Element Method [...] Read more.
This paper investigated the effect of sensor density and alignment for three-dimensional shape sensing of an airplane-wing-shaped thick panel subjected to three different loading conditions, i.e., bending, torsion, and membrane loads. For shape sensing analysis of the panel, the Inverse Finite Element Method (iFEM) was used together with the Refined Zigzag Theory (RZT), in order to enable accurate predictions for transverse deflection and through-the-thickness variation of interfacial displacements. In this study, the iFEM-RZT algorithm is implemented by utilizing a novel three-node C°-continuous inverse-shell element, known as i3-RZT. The discrete strain data is generated numerically through performing a high-fidelity finite element analysis on the wing-shaped panel. This numerical strain data represents experimental strain readings obtained from surface patched strain gauges or embedded fiber Bragg grating (FBG) sensors. Three different sensor placement configurations with varying density and alignment of strain data were examined and their corresponding displacement contours were compared with those of reference solutions. The results indicate that a sparse distribution of FBG sensors (uniaxial strain measurements), aligned in only the longitudinal direction, is sufficient for predicting accurate full-field membrane and bending responses (deformed shapes) of the panel, including a true zigzag representation of interfacial displacements. On the other hand, a sparse deployment of strain rosettes (triaxial strain measurements) is essentially enough to produce torsion shapes that are as accurate as those of predicted by a dense sensor placement configuration. Hence, the potential applicability and practical aspects of i3-RZT/iFEM methodology is proven for three-dimensional shape-sensing of future aerospace structures. Full article
(This article belongs to the Special Issue Sensor Technologies for Health Monitoring of Composite Structures)
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6291 KiB  
Article
Stretchable, Highly Durable Ternary Nanocomposite Strain Sensor for Structural Health Monitoring of Flexible Aircraft
by Feng Yin, Dong Ye, Chen Zhu, Lei Qiu and YongAn Huang
Sensors 2017, 17(11), 2677; https://doi.org/10.3390/s17112677 - 20 Nov 2017
Cited by 91 | Viewed by 8622
Abstract
Harmonious developments of electrical and mechanical performances are crucial for stretchable sensors in structural health monitoring (SHM) of flexible aircraft such as aerostats and morphing aircrafts. In this study, we prepared a highly durable ternary conductive nanocomposite made of polydimethylsiloxane (PDMS), carbon black [...] Read more.
Harmonious developments of electrical and mechanical performances are crucial for stretchable sensors in structural health monitoring (SHM) of flexible aircraft such as aerostats and morphing aircrafts. In this study, we prepared a highly durable ternary conductive nanocomposite made of polydimethylsiloxane (PDMS), carbon black (CB) and multi-walled carbon nanotubes (MWCNTs) to fabricate stretchable strain sensors. The nanocomposite has excellent electrical and mechanical properties by intensively optimizing the weight percentage of conducting fillers as well as the ratio of PDMS pre-polymer and curing agent. It was found that the nanocomposite with homogeneous hybrid filler of 1.75 wt % CB and 3 wt % MWCNTs exhibits a highly strain sensitive characteristics of good linearity, high gauge factor (GF ~ 12.25) and excellent durability over 105 stretching-releasing cycles under a tensile strain up to 25% when the PDMS was prepared at the ratio of 12.5:1. A strain measurement of crack detection for the aerostats surface was also employed, demonstrating a great potential of such ternary nanocomposite used as stretchable strain sensor in SHM. Full article
(This article belongs to the Special Issue Sensor Technologies for Health Monitoring of Composite Structures)
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2834 KiB  
Article
A Pattern Recognition Approach to Acoustic Emission Data Originating from Fatigue of Wind Turbine Blades
by Jialin Tang, Slim Soua, Cristinel Mares and Tat-Hean Gan
Sensors 2017, 17(11), 2507; https://doi.org/10.3390/s17112507 - 1 Nov 2017
Cited by 58 | Viewed by 6145
Abstract
The identification of particular types of damage in wind turbine blades using acoustic emission (AE) techniques is a significant emerging field. In this work, a 45.7-m turbine blade was subjected to flap-wise fatigue loading for 21 days, during which AE was measured by [...] Read more.
The identification of particular types of damage in wind turbine blades using acoustic emission (AE) techniques is a significant emerging field. In this work, a 45.7-m turbine blade was subjected to flap-wise fatigue loading for 21 days, during which AE was measured by internally mounted piezoelectric sensors. This paper focuses on using unsupervised pattern recognition methods to characterize different AE activities corresponding to different fracture mechanisms. A sequential feature selection method based on a k-means clustering algorithm is used to achieve a fine classification accuracy. The visualization of clusters in peak frequency−frequency centroid features is used to correlate the clustering results with failure modes. The positions of these clusters in time domain features, average frequency−MARSE, and average frequency−peak amplitude are also presented in this paper (where MARSE represents the Measured Area under Rectified Signal Envelope). The results show that these parameters are representative for the classification of the failure modes. Full article
(This article belongs to the Special Issue Sensor Technologies for Health Monitoring of Composite Structures)
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3909 KiB  
Article
Brillouin Optical Correlation Domain Analysis in Composite Material Beams
by Yonatan Stern, Yosef London, Eyal Preter, Yair Antman, Hilel Hagai Diamandi, Maayan Silbiger, Gadi Adler, Eyal Levenberg, Doron Shalev and Avi Zadok
Sensors 2017, 17(10), 2266; https://doi.org/10.3390/s17102266 - 2 Oct 2017
Cited by 5 | Viewed by 4595
Abstract
Structural health monitoring is a critical requirement in many composites. Numerous monitoring strategies rely on measurements of temperature or strain (or both), however these are often restricted to point-sensing or to the coverage of small areas. Spatially-continuous data can be obtained with optical [...] Read more.
Structural health monitoring is a critical requirement in many composites. Numerous monitoring strategies rely on measurements of temperature or strain (or both), however these are often restricted to point-sensing or to the coverage of small areas. Spatially-continuous data can be obtained with optical fiber sensors. In this work, we report high-resolution distributed Brillouin sensing over standard fibers that are embedded in composite structures. A phase-coded, Brillouin optical correlation domain analysis (B-OCDA) protocol was employed, with spatial resolution of 2 cm and sensitivity of 1 °K or 20 micro-strain. A portable measurement setup was designed and assembled on the premises of a composite structures manufacturer. The setup was successfully utilized in several structural health monitoring scenarios: (a) monitoring the production and curing of a composite beam over 60 h; (b) estimating the stiffness and Young’s modulus of a composite beam; and (c) distributed strain measurements across the surfaces of a model wing of an unmanned aerial vehicle. The measurements are supported by the predictions of structural analysis calculations. The results illustrate the potential added values of high-resolution, distributed Brillouin sensing in the structural health monitoring of composites. Full article
(This article belongs to the Special Issue Sensor Technologies for Health Monitoring of Composite Structures)
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2637 KiB  
Article
Fibre Bragg Gratings in Embedded Microstructured Optical Fibres Allow Distinguishing between Symmetric and Anti-Symmetric Lamb Waves in Carbon Fibre Reinforced Composites
by Ben De Pauw, Sidney Goossens, Thomas Geernaert, Dimitrios Habas, Hugo Thienpont and Francis Berghmans
Sensors 2017, 17(9), 1948; https://doi.org/10.3390/s17091948 - 24 Aug 2017
Cited by 10 | Viewed by 5650
Abstract
Conventional contact sensors used for Lamb wave-based ultrasonic inspection, such as piezo-electric transducers, measure omnidirectional strain and do not allow distinguishing between fundamental symmetric and anti-symmetric modes. In this paper, we show that the use of a single fibre Bragg grating created in [...] Read more.
Conventional contact sensors used for Lamb wave-based ultrasonic inspection, such as piezo-electric transducers, measure omnidirectional strain and do not allow distinguishing between fundamental symmetric and anti-symmetric modes. In this paper, we show that the use of a single fibre Bragg grating created in a dedicated microstructured optical fibre allows one to directly make the distinction between these fundamental Lamb wave modes. This feature stems from the different sensitivities of the microstructured fibre to axial and transverse strain. We fabricated carbon fibre-reinforced polymer panels equipped with embedded microstructured optical fibre sensors and experimentally demonstrated the strain waves associated with the propagating Lamb waves in both the axial and transverse directions of the optical fibre. Full article
(This article belongs to the Special Issue Sensor Technologies for Health Monitoring of Composite Structures)
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4702 KiB  
Article
Influence of the Spatial Dimensions of Ultrasonic Transducers on the Frequency Spectrum of Guided Waves
by Vykintas Samaitis and Liudas Mažeika
Sensors 2017, 17(8), 1825; https://doi.org/10.3390/s17081825 - 8 Aug 2017
Cited by 6 | Viewed by 5053
Abstract
Ultrasonic guided wave (UGW)-based condition monitoring has shown great promise in detecting, localizing, and characterizing damage in complex systems. However, the application of guided waves for damage detection is challenging due to the existence of multiple modes and dispersion. This results in distorted [...] Read more.
Ultrasonic guided wave (UGW)-based condition monitoring has shown great promise in detecting, localizing, and characterizing damage in complex systems. However, the application of guided waves for damage detection is challenging due to the existence of multiple modes and dispersion. This results in distorted wave packets with limited resolution and the interference of multiple reflected modes. To develop reliable inspection systems, either the transducers have to be optimized to generate a desired single mode of guided waves with known dispersive properties, or the frequency responses of all modes present in the structure must be known to predict wave interaction. Currently, there is a lack of methods to predict the response spectrum of guided wave modes, especially in cases when multiple modes are being excited simultaneously. Such methods are of vital importance for further understanding wave propagation within the structures as well as wave-damage interaction. In this study, a novel method to predict the response spectrum of guided wave modes was proposed based on Fourier analysis of the particle velocity distribution on the excitation area. The method proposed in this study estimates an excitability function based on the spatial dimensions of the transducer, type of vibration, and dispersive properties of the medium. As a result, the response amplitude as a function of frequency for each guided wave mode present in the structure can be separately obtained. The method was validated with numerical simulations on the aluminum and glass fiber composite samples. The key findings showed that it can be applied to estimate the response spectrum of a guided wave mode on any type of material (either isotropic structures, or multi layered anisotropic composites) and under any type of excitation if the phase velocity dispersion curve and the particle velocity distribution of the wave source was known initially. Thus, the proposed method may be a beneficial tool to explain and predict the response spectrum of guided waves throughout the development of any structural health monitoring system. Full article
(This article belongs to the Special Issue Sensor Technologies for Health Monitoring of Composite Structures)
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1944 KiB  
Article
Adhesive Defect Monitoring of Glass Fiber Epoxy Plate Using an Impedance-Based Non-Destructive Testing Method for Multiple Structures
by Wongi S. Na and Jongdae Baek
Sensors 2017, 17(6), 1439; https://doi.org/10.3390/s17061439 - 19 Jun 2017
Cited by 6 | Viewed by 6090
Abstract
The emergence of composite materials has revolutionized the approach to building engineering structures. With the number of applications for composites increasing every day, maintaining structural integrity is of utmost importance. For composites, adhesive bonding is usually the preferred choice over the mechanical fastening [...] Read more.
The emergence of composite materials has revolutionized the approach to building engineering structures. With the number of applications for composites increasing every day, maintaining structural integrity is of utmost importance. For composites, adhesive bonding is usually the preferred choice over the mechanical fastening method, and monitoring for delamination is an essential factor in the field of composite materials. In this study, a non-destructive method known as the electromechanical impedance method is used with an approach of monitoring multiple areas by specifying certain frequency ranges to correspond to a certain test specimen. Experiments are conducted using various numbers of stacks created by attaching glass fiber epoxy composite plates onto one another, and two different debonding damage types are introduced to evaluate the performance of the multiple monitoring electromechanical impedance method. Full article
(This article belongs to the Special Issue Sensor Technologies for Health Monitoring of Composite Structures)
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4891 KiB  
Article
Long-Term In-Service Monitoring and Performance Assessment of the Main Cables of Long-Span Suspension Bridges
by Yang Deng, Yang Liu and Suren Chen
Sensors 2017, 17(6), 1414; https://doi.org/10.3390/s17061414 - 16 Jun 2017
Cited by 24 | Viewed by 6567
Abstract
Despite the recent developments in structural health monitoring, there remain great challenges for accurately, conveniently, and economically assessing the in-service performance of the main cables for long-span suspension bridges. A long-term structural health monitoring technique is developed to measure the tension force with [...] Read more.
Despite the recent developments in structural health monitoring, there remain great challenges for accurately, conveniently, and economically assessing the in-service performance of the main cables for long-span suspension bridges. A long-term structural health monitoring technique is developed to measure the tension force with a conventional sensing technology and further provide the in-service performance assessment strategy of the main cable. The monitoring system adopts conventional vibrating strings transducers to monitor the tension forces of separate cable strands of the main cable in the anchor span. The performance evaluation of the main cable is conducted based on the collected health monitoring data: (1) the measured strand forces are used to derive the overall tension force of a main cable, which is further translated into load bearing capacity assessment using the concept of safety factor; and (2) the proposed technique can also evaluate the uniformity of tension forces from different cable strands. The assessment of uniformity of strand forces of a main cable offers critical information in terms of potential risks of partial damage and performance deterioration of the main cable. The results suggest the proposed low-cost monitoring system is an option to provide approximate estimation of tension forces of main cables for suspension bridges. With the long-term monitoring data, the proposed monitoring-based evaluation methods can further provide critical information to assess the safety and serviceability performance of main cables. Full article
(This article belongs to the Special Issue Sensor Technologies for Health Monitoring of Composite Structures)
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5936 KiB  
Article
Artificial Neural Network-Based Early-Age Concrete Strength Monitoring Using Dynamic Response Signals
by Junkyeong Kim, Chaggil Lee and Seunghee Park
Sensors 2017, 17(6), 1319; https://doi.org/10.3390/s17061319 - 7 Jun 2017
Cited by 30 | Viewed by 5277
Abstract
Concrete is one of the most common materials used to construct a variety of civil infrastructures. However, since concrete might be susceptible to brittle fracture, it is essential to confirm the strength of concrete at the early-age stage of the curing process to [...] Read more.
Concrete is one of the most common materials used to construct a variety of civil infrastructures. However, since concrete might be susceptible to brittle fracture, it is essential to confirm the strength of concrete at the early-age stage of the curing process to prevent unexpected collapse. To address this issue, this study proposes a novel method to estimate the early-age strength of concrete, by integrating an artificial neural network algorithm with a dynamic response measurement of the concrete material. The dynamic response signals of the concrete, including both electromechanical impedances and guided ultrasonic waves, are obtained from an embedded piezoelectric sensor module. The cross-correlation coefficient of the electromechanical impedance signals and the amplitude of the guided ultrasonic wave signals are selected to quantify the variation in dynamic responses according to the strength of the concrete. Furthermore, an artificial neural network algorithm is used to verify a relationship between the variation in dynamic response signals and concrete strength. The results of an experimental study confirm that the proposed approach can be effectively applied to estimate the strength of concrete material from the early-age stage of the curing process. Full article
(This article belongs to the Special Issue Sensor Technologies for Health Monitoring of Composite Structures)
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12722 KiB  
Article
Impact Damage Localisation with Piezoelectric Sensors under Operational and Environmental Conditions
by Mohammad Saleh Salmanpour, Zahra Sharif Khodaei and M. H. Ferri Aliabadi
Sensors 2017, 17(5), 1178; https://doi.org/10.3390/s17051178 - 22 May 2017
Cited by 66 | Viewed by 7302
Abstract
Guided-wave structural health monitoring (SHM) systems with piezoelectric sensors are investigated for localisation of barely visible impact damage in CFRP plates under vibration and different thermal conditions. A single baseline set is used in a delay-and-sum algorithm with temperature correction for damage localisation [...] Read more.
Guided-wave structural health monitoring (SHM) systems with piezoelectric sensors are investigated for localisation of barely visible impact damage in CFRP plates under vibration and different thermal conditions. A single baseline set is used in a delay-and-sum algorithm with temperature correction for damage localisation in a large temperature range. Damage localisation is also demonstrated under transient thermal conditions, with signals recorded while the temperature is rapidly decreased. Damage severity due to successive impact events is studied under constant temperature. Damage is also localised when the plate is subjected to random vibration. Full article
(This article belongs to the Special Issue Sensor Technologies for Health Monitoring of Composite Structures)
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4467 KiB  
Article
Structural Analysis of Polymer Composites Using Spectral Domain Optical Coherence Tomography
by Muhammad Faizan Shirazi, Mansik Jeon and Jeehyun Kim
Sensors 2017, 17(5), 1155; https://doi.org/10.3390/s17051155 - 18 May 2017
Cited by 11 | Viewed by 5304
Abstract
The structural analysis of nylon/graphene oxide (NY/GO) and polyetherblockamide/ trisilinolphenyl-polyhederal oligomeric silsesquioxane (PEBA/t-POSS) composites were performed using high-resolution spectral domain optical coherence tomography (SD-OCT). This optical technology revealed both cross-sectional, as well as sub-layer depth information of sample. The non-destructive real-time imaging demonstrated [...] Read more.
The structural analysis of nylon/graphene oxide (NY/GO) and polyetherblockamide/ trisilinolphenyl-polyhederal oligomeric silsesquioxane (PEBA/t-POSS) composites were performed using high-resolution spectral domain optical coherence tomography (SD-OCT). This optical technology revealed both cross-sectional, as well as sub-layer depth information of sample. The non-destructive real-time imaging demonstrated the nature of defects in the composites. The thickness and location of each defect point in the composites were measured using A-scan analysis on the SD-OCT images. The cross-sectional and volumetric images clearly demonstrate the effectiveness of SD-OCT for composite research, as well as the for industrial quality assurance of polymer materials. Full article
(This article belongs to the Special Issue Sensor Technologies for Health Monitoring of Composite Structures)
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4390 KiB  
Article
A Modified Lamb Wave Time-Reversal Method for Health Monitoring of Composite Structures
by Liang Zeng, Jing Lin and Liping Huang
Sensors 2017, 17(5), 955; https://doi.org/10.3390/s17050955 - 26 Apr 2017
Cited by 34 | Viewed by 5905
Abstract
Because the time reversal operator of Lamb waves varies with frequency in composite structures, the reconstructed signal deviates from the input signal even in undamaged cases. The damage index captures the discrepancy between the two signals without differentiating the effects of time reversal [...] Read more.
Because the time reversal operator of Lamb waves varies with frequency in composite structures, the reconstructed signal deviates from the input signal even in undamaged cases. The damage index captures the discrepancy between the two signals without differentiating the effects of time reversal operator from those of damage. This results in the risk of false alarm. To solve this issue, a modified time reversal method (MTRM) is proposed. In this method, the frequency dependence of the time reversal operator is compensated by two steps. First, an amplitude modulation is placed on the input signal, which is related to the excitability, detectability, and attenuation of the Lamb wave mode. Second, the damage index is redefined to measure the deviation between the reconstructed signal and the modulated input signal. This could indicate the presence of damage with better performance. An experimental investigation is then conducted on a carbon fiber-reinforced polymer (CFRP) laminate to illustrate the effectiveness of the MTRM for identifying damage. The results show that the MTRM may provide a promising tool for health monitoring of composite structures. Full article
(This article belongs to the Special Issue Sensor Technologies for Health Monitoring of Composite Structures)
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1230 KiB  
Article
Simulation Study of the Localization of a Near-Surface Crack Using an Air-Coupled Ultrasonic Sensor Array
by Steven Delrue, Vladislav Aleshin, Mikael Sørensen and Lieven De Lathauwer
Sensors 2017, 17(4), 930; https://doi.org/10.3390/s17040930 - 22 Apr 2017
Cited by 8 | Viewed by 5438
Abstract
The importance of Non-Destructive Testing (NDT) to check the integrity of materials in different fields of industry has increased significantly in recent years. Actually, industry demands NDT methods that allow fast (preferably non-contact) detection and localization of early-stage defects with easy-to-interpret results, so [...] Read more.
The importance of Non-Destructive Testing (NDT) to check the integrity of materials in different fields of industry has increased significantly in recent years. Actually, industry demands NDT methods that allow fast (preferably non-contact) detection and localization of early-stage defects with easy-to-interpret results, so that even a non-expert field worker can carry out the testing. The main challenge is to combine as many of these requirements into one single technique. The concept of acoustic cameras, developed for low frequency NDT, meets most of the above-mentioned requirements. These cameras make use of an array of microphones to visualize noise sources by estimating the Direction Of Arrival (DOA) of the impinging sound waves. Until now, however, because of limitations in the frequency range and the lack of integrated nonlinear post-processing, acoustic camera systems have never been used for the localization of incipient damage. The goal of the current paper is to numerically investigate the capabilities of locating incipient damage by measuring the nonlinear airborne emission of the defect using a non-contact ultrasonic sensor array. We will consider a simple case of a sample with a single near-surface crack and prove that after efficient excitation of the defect sample, the nonlinear defect responses can be detected by a uniform linear sensor array. These responses are then used to determine the location of the defect by means of three different DOA algorithms. The results obtained in this study can be considered as a first step towards the development of a nonlinear ultrasonic camera system, comprising the ultrasonic sensor array as the hardware and nonlinear post-processing and source localization software. Full article
(This article belongs to the Special Issue Sensor Technologies for Health Monitoring of Composite Structures)
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