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18 pages, 9424 KiB

Open AccessArticle

Guided Wave-Convolutional Neural Network Based Fatigue Crack Diagnosis of Aircraft Structures

by Liang Xu, Shenfang Yuan, Jian Chen and Yuanqiang Ren

Sensors 2019, 19(16), 3567; https://doi.org/10.3390/s19163567 - 15 Aug 2019

Cited by 50 | Viewed by 4957

Fatigue crack diagnosis (FCD) is of great significance for ensuring safe operation, prolonging service time and reducing maintenance cost in aircrafts and many other safety-critical systems. As a promising method, the guided wave (GW)-based structural health monitoring method has been widely investigated for [...] Read more.

Fatigue crack diagnosis (FCD) is of great significance for ensuring safe operation, prolonging service time and reducing maintenance cost in aircrafts and many other safety-critical systems. As a promising method, the guided wave (GW)-based structural health monitoring method has been widely investigated for FCD. However, reliable FCD still meets challenges, because uncertainties in real engineering applications usually cause serious change both to the crack propagation itself and GW monitoring signals. As one of deep learning methods, convolutional neural network (CNN) owns the ability of fusing a large amount of data, extracting high-level feature expressions related to classification, which provides a potential new technology to be applied in the GW-structural health monitoring method for crack evaluation. To address the influence of dispersion on reliable FCD, in this paper, a GW-CNN based FCD method is proposed. In this method, multiple damage indexes (DIs) from multiple GW exciting-acquisition channels are extracted. A CNN is designed and trained to further extract high-level features from the multiple DIs and implement feature fusion for crack evaluation. Fatigue tests on a typical kind of aircraft structure are performed to validate the proposed method. The results show that the proposed method can effectively reduce the influence of uncertainties on FCD, which is promising for real engineering applications. Full article

(This article belongs to the Special Issue Selected Papers from 7th Asia-Pacific Workshop on Structural Health Monitoring 2018 (APWSHM 2018))

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14 pages, 10637 KiB

Open AccessArticle

Extraction Method of Crack Signal for Inspection of Complicated Steel Structures Using A Dual-Channel Magnetic Sensor

by Minoru Hayashi, Taisuke Saito, Yoshihiro Nakamura, Kenji Sakai, Toshihiko Kiwa, Izumi Tanikura and Keiji Tsukada

Sensors 2019, 19(13), 3001; https://doi.org/10.3390/s19133001 - 8 Jul 2019

Cited by 9 | Viewed by 3564

Abstract

Conventional eddy current testing (ECT) using a pickup coil probe is widely employed for the detection of structural cracks. However, the inspection of conventional ECT for steel structures is difficult because of the magnetic noise caused by the nonuniform permeability of steel. To [...] Read more.

Conventional eddy current testing (ECT) using a pickup coil probe is widely employed for the detection of structural cracks. However, the inspection of conventional ECT for steel structures is difficult because of the magnetic noise caused by the nonuniform permeability of steel. To combat this challenge, we have developed a small magnetic sensor probe with a dual-channel tunneling magnetoresistance sensor that is capable of reducing magnetic noise. Applying this probe to a complicated component of steel structures—such as the welds joining a U-shaped rib and deck plate together—requires the reduction of signal fluctuation caused by the distance (liftoff) variations between the sensor probe and the subject. In this study, the fundamental crack signal and the liftoff signal were investigated with the dual-channel sensor. The results showed that the liftoff signals could be reduced and differentiated from the crack signals by the differential parameters of the dual-channel sensor. In addition, we proposed an extraction technique for the crack signal using the Lissajous curve of the differential parameters. The extraction technique could be applied to the inspections not only for flat plates but also for welded angles to detect cracks without the influence of the liftoff signal. Full article

(This article belongs to the Special Issue Selected Papers from 7th Asia-Pacific Workshop on Structural Health Monitoring 2018 (APWSHM 2018))

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22 pages, 12660 KiB

Open AccessArticle

An Investigation on a Quantitative Tomographic SHM Technique for a Containment Liner Plate in a Nuclear Power Plant with Guided Wave Mode Selection

by Yonghee Lee and Younho Cho

Sensors 2019, 19(12), 2819; https://doi.org/10.3390/s19122819 - 24 Jun 2019

Cited by 7 | Viewed by 3854

Abstract

The containment liner plate (CLP) in a nuclear power plant is the most critical part of the structure of a power plant, as it prevents the radioactive contamination of the surrounding area. This paper presents feasibility of structural health monitoring (SHM) and an [...] Read more.

The containment liner plate (CLP) in a nuclear power plant is the most critical part of the structure of a power plant, as it prevents the radioactive contamination of the surrounding area. This paper presents feasibility of structural health monitoring (SHM) and an elastic wave tomography method based on ultrasonic guided waves (GW), for evaluating the integrity of CLP. It aims to check the integrity for a dynamic response to a damaged isotropic structure. The proposed SHM technique relies on sensors and, therefore, it can be placed on the structure permanently and can monitor either passively or actively. For applying this method, a suitable guided wave mode tuning is required to verify wave propagation. A finite element analysis (FEA) is performed to figure out the suitable GW mode for a CLP by considering geometric and material condition. Furthermore, elastic wave tomography technique is modified to evaluate the CLP condition and its visualization. A modified reconstruction algorithm for the probabilistic inspection of damage tomography algorithm is used to quantify corrosion defects in the CLP. The location and shape of the wall-thinning defects are successfully obtained by using elastic GW based SHM. Making full use of verified GW mode to Omni-directional transducer, it can be expected to improve utilization of the SHM based evaluation technique for CLP. Full article

(This article belongs to the Special Issue Selected Papers from 7th Asia-Pacific Workshop on Structural Health Monitoring 2018 (APWSHM 2018))

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14 pages, 7407 KiB

Open AccessArticle

A Spray-on, Nanocomposite-Based Sensor Network for in-Situ Active Structural Health Monitoring

by Wuxiong Cao, Pengyu Zhou, Yaozhong Liao, Xiongbin Yang, Dongyue Pan, Yehai Li, Baojun Pang, Li-min Zhou and Zhongqing Su

Sensors 2019, 19(9), 2077; https://doi.org/10.3390/s19092077 - 4 May 2019

Cited by 21 | Viewed by 3419

Abstract

A new breed of nanocomposite-based spray-on sensor is developed for in-situ active structural health monitoring (SHM). The novel nanocomposite sensor is rigorously designed with graphene as the nanofiller and polyvinylpyrrolidone (PVP) as the matrix, fabricated using a simple spray deposition process. Electrical analysis, [...] Read more.

A new breed of nanocomposite-based spray-on sensor is developed for in-situ active structural health monitoring (SHM). The novel nanocomposite sensor is rigorously designed with graphene as the nanofiller and polyvinylpyrrolidone (PVP) as the matrix, fabricated using a simple spray deposition process. Electrical analysis, as well as morphological characterization of the spray-on sensor, was conducted to investigate percolation characteristic, in which the optimal threshold (~0.91%) of the graphene/PVP sensor was determined. Owing to the uniform and stable conductive network formed by well-dispersed graphene nanosheets in the PVP matrix, the tailor-made spray-on sensor exhibited excellent piezoresistive performance. By virtue of the tunneling effect of the conductive network, the sensor was proven to be capable of perceiving signals of guided ultrasonic waves (GUWs) with ultrahigh frequency up to 500 kHz. Lightweight and flexible, the spray-on nanocomposite sensor demonstrated superior sensitivity, high fidelity, and high signal-to-noise ratio under dynamic strain with ultralow magnitude (of the order of micro-strain) that is comparable with commercial lead zirconate titanate (PZT) wafers. The sensors were further networked to perform damage characterization, and the results indicate significant application potential of the spray-on nanocomposite-based sensor for in-situ active GUW-based SHM. Full article

(This article belongs to the Special Issue Selected Papers from 7th Asia-Pacific Workshop on Structural Health Monitoring 2018 (APWSHM 2018))

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22 pages, 7943 KiB

Open AccessArticle

Wireless Sensor Networks Composed of Standard Microcomputers and Smartphones for Applications in Structural Health Monitoring

by Guido Morgenthal, Jan Frederick Eick, Sebastian Rau and Jakob Taraben

Sensors 2019, 19(9), 2070; https://doi.org/10.3390/s19092070 - 3 May 2019

Cited by 13 | Viewed by 5549

Abstract

Wireless sensor networks have attracted great attention for applications in structural health monitoring due to their ease of use, flexibility of deployment, and cost-effectiveness. This paper presents a software framework for WiFi-based wireless sensor networks composed of low-cost mass market single-board computers. A [...] Read more.

Wireless sensor networks have attracted great attention for applications in structural health monitoring due to their ease of use, flexibility of deployment, and cost-effectiveness. This paper presents a software framework for WiFi-based wireless sensor networks composed of low-cost mass market single-board computers. A number of specific system-level software components were developed to enable robust data acquisition, data processing, sensor network communication, and timing with a focus on structural health monitoring (SHM) applications. The framework was validated on Raspberry Pi computers, and its performance was studied in detail. The paper presents several characteristics of the measurement quality such as sampling accuracy and time synchronization and discusses the specific limitations of the system. The implementation includes a complementary smartphone application that is utilized for data acquisition, visualization, and analysis. A prototypical implementation further demonstrates the feasibility of integrating smartphones as data acquisition nodes into the network, utilizing their internal sensors. The measurement system was employed in several monitoring campaigns, three of which are documented in detail. The suitability of the system is evaluated based on comparisons of target quantities with reference measurements. The results indicate that the presented system can robustly achieve a measurement performance commensurate with that required in many typical SHM tasks such as modal identification. As such, it represents a cost-effective alternative to more traditional monitoring solutions. Full article

(This article belongs to the Special Issue Selected Papers from 7th Asia-Pacific Workshop on Structural Health Monitoring 2018 (APWSHM 2018))

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18 pages, 8357 KiB

Open AccessArticle

A Study of Sensor Placement Optimization Problem for Guided Wave-Based Damage Detection

by Rohan Soman, Pawel Kudela, Kaleeswaran Balasubramaniam, Shishir Kumar Singh and Pawel Malinowski

Sensors 2019, 19(8), 1856; https://doi.org/10.3390/s19081856 - 18 Apr 2019

Cited by 40 | Viewed by 5747

Abstract

Guided waves (GW) allow fast inspection of a large area and hence have attracted research interest from the structural health monitoring (SHM) community. Thus, GW-based SHM is ideal for thin structures such as plates, pipes, etc., and is finding applications in several fields [...] Read more.

Guided waves (GW) allow fast inspection of a large area and hence have attracted research interest from the structural health monitoring (SHM) community. Thus, GW-based SHM is ideal for thin structures such as plates, pipes, etc., and is finding applications in several fields like aerospace, automotive, wind energy, etc. The GW propagate along the surface of the sample and get reflected from discontinuities in the structure in the form of boundaries and damage. Through proper signal processing of the reflected waves based on their time of arrival, the damage can be detected and isolated. For complex structures, a higher number of sensors may be required, which increases the cost of the equipment, as well as the mass. Thus, there is an effort to reduce the number of sensors without compromising the quality of the monitoring achieved. It is of utmost importance that the entire structure can be investigated. Hence, it is necessary to optimize the locations of the sensors in order to maximize the coverage while limiting the number of sensors used. A genetic algorithm (GA)-based optimization strategy was proposed by the authors for use in a simple aluminum plate. This paper extends the optimization methodology for other shape plates and presents experimental, analytical, and numerical studies. The sensitivity studies have been carried out by changing the relative weights of the application demands and presented in the form of a Pareto front. The Pareto front allows comparison of the relative importance of the different application demands, and an appropriate choice can be made based on the information provided. Full article

(This article belongs to the Special Issue Selected Papers from 7th Asia-Pacific Workshop on Structural Health Monitoring 2018 (APWSHM 2018))

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14 pages, 3156 KiB

Open AccessArticle

Towards a Non-Invasive Technique for Healing Assessment of Internally Fixated Femur

by Wing Kong Chiu, Benjamin Steven Vien, Matthias Russ and Mark Fitzgerald

Sensors 2019, 19(4), 857; https://doi.org/10.3390/s19040857 - 19 Feb 2019

Cited by 15 | Viewed by 4655

Abstract

The lack of a quantitative method to adequately assess fractured bone healing that has undergone fixation limits prognostic capabilities on patients’ optimal return to work. This paper addresses the use of vibrational analysis to monitor the state of healing of a plate-screw fixated [...] Read more.

The lack of a quantitative method to adequately assess fractured bone healing that has undergone fixation limits prognostic capabilities on patients’ optimal return to work. This paper addresses the use of vibrational analysis to monitor the state of healing of a plate-screw fixated femur and supplement the current clinical radiographic assessment. This experimental study involves an osteotomised composite femur specimen enclosed by modelling clay to simulate the damping effect of overlying soft tissues. Epoxy adhesives are applied to the fractured region and to simulate the healing process. With the instrumentation described, the cross-spectrum and coherence are obtained and analysed in the frequency domain over a period of time. The results suggest that it is crucial to analyse the cross-spectrum and proposed healing index to quantitatively assess the stages of healing. The results also show that the mass loading effect due to modelling clay did not influence the proposed healing assessment technique. The findings indicate a potential non-intrusive technique to evaluate the healing of fractured femur by utilising the vibrational responses. Full article

(This article belongs to the Special Issue Selected Papers from 7th Asia-Pacific Workshop on Structural Health Monitoring 2018 (APWSHM 2018))

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9 pages, 3998 KiB

Open AccessArticle

Critical Excitation of the Fundamental Quasi-Shear Mode Wave in Waveguide Bars for Elevated Temperature Applications

by Jiuhong Jia, Zuoyu Liao, Xiaotao Cai, Yun Tu and Shan-Tung Tu

Sensors 2019, 19(4), 793; https://doi.org/10.3390/s19040793 - 15 Feb 2019

Cited by 8 | Viewed by 2595

Abstract

The safety of critical pressure equipment in elevated temperature is increasingly important. Moreover, the on-line monitoring method is potentially useful to improve their safety. A waveguide bar system can enable monitoring of critical equipment working in elevated temperature using reliable ultrasonic technology. Among [...] Read more.

The safety of critical pressure equipment in elevated temperature is increasingly important. Moreover, the on-line monitoring method is potentially useful to improve their safety. A waveguide bar system can enable monitoring of critical equipment working in elevated temperature using reliable ultrasonic technology. Among the waveguide bar system, the matching mechanism of the transducer and the waveguide bar is crucial to propagate the pure fundamental quasi-shear mode (shorten for SH0*) wave. In the present research, the loading line sources that can excite pure SH0* wave are investigated and the anti-plane shear loading source is selected. The critical values about the geometric dimensions of the junctions between the piezoelectric transducer and the waveguide bar are explored by simulation and experiments. On the condition that the excitation sources satisfy the critical values, the loading can be approximated to an anti-plane shear one to excite the pure SH0* wave. Some waveguide bar systems are designed based on the simulated critical values and some experiments at high temperature are carried out. The experimental results verify that the designed waveguide bar systems can excite the pure SH0* wave at elevated temperatures, which verify the reliability of the simulated critical results. Full article

(This article belongs to the Special Issue Selected Papers from 7th Asia-Pacific Workshop on Structural Health Monitoring 2018 (APWSHM 2018))

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