Fiber Bragg Grating Acoustic Emission Research Articles

Online Diagnosis of Small Faults in Rolling Bearings Using FBG Acoustic Emission Sensors Inside the Accelerated Life Tester

Rolling bearings are widely used in many industries and their online diagnosis is very important. However, there is still no effective way to detect small faults online. In this article, a fiber Bragg grating (FBG) acoustic emission (AE) sensing method is proposed and tested inside an accelerated bearing life tester (ABLT). The FBGAE sensors are small, resistant to electromagnetic interference, intrinsically explosion-proof, and are thus fit for the inner environment of an ABLT, which is small, has high electromagnetic interference, and is full of lubrication oil. Therefore, we could install the FBG AE sensors inside an ABLT. The experimental system based on the principle of tunable narrowband laser demodulation is built up to collect the AE signals of faulty rolling bearings with different fault types. Then, with the envelope demodulation algorithm, we obtained the fault characteristic frequencies of the bearings that were consistent with the theoretical fault frequencies. The results show that the FBG AE sensors are sensitive to the small faults of rolling bearings and can be used inside an ABLT.

Image Classification-Based Defect Detection of Railway Tracks Using Fiber Bragg Grating Ultrasonic Sensors

Structural health monitoring (SHM) is vital to the maintenance of civil infrastructures. For rail transit systems, early defect detection of rail tracks can effectively prevent the occurrence of severe accidents like derailment. Non-destructive testing (NDT) has been implemented in railway online and offline monitoring systems using state-of-the-art sensing technologies. Data-driven methodologies, especially machine learning, have contributed significantly to modern NDT approaches. In this paper, an efficient and robust image classification model is proposed to achieve railway status identification using ultrasonic guided waves (UGWs). Experimental studies are conducted using a hybrid sensing system consisting of a lead–zirconate–titanate (PZT) actuator and fiber Bragg grating (FBG) sensors. Comparative studies have been firstly carried out to evaluate the performance of the UGW signals obtained by FBG sensors and high-resolution acoustic emission (AE) sensors. Three different rail web conditions are considered in this research, where the rail is: (1) intact without any defect; (2) damaged with an artificial crack; and (3) damaged with a bump on the surface made of blu-tack adhesives. The signals acquired by FBG sensors and AE sensors are compared in time and frequency domains. Then the research focuses on damage detection using a convolutional neural network (CNN) with the input of RGB spectrum images of the UGW signals acquired by FBG sensors, which are calculated using Short-time Fourier Transform (STFT). The proposed image classifier achieves high accuracy in predicting each railway condition. The visualization of the classifier indicates the high efficiency of the proposed paradigm, revealing the potential of the method to be applied to mass railway monitoring systems in the future.

Design of a novel fiber grating acoustic emission sensor based on coupling cone structure

A novel fiber Bragg grating (FBG) acoustic emission (AE) sensor based on coupling cone structure is proposed in this paper, which is flexible and reusable. The sensor is fabricated by additive manufacturing technology. The numerical modeling of the coupling cone structure was performed using finite element analysis. The influence of the coupling cone angle and material on the AE detection performance was studied. The main parameters of the coupling cone structure are determined. The AE detection of material tensile tests was studied by edge-filter-demodulation of spectrum technology. The experimental results demonstrated that the coupling cone FBG AE (Cone-FBG-AE) sensor has advantages of high sensitivity, flexibility and adjustable positioning, and can be reused. It realizes real-time monitoring of AE signals in the tensile process of the specimen, which is consistent with the effect of the resonant AE sensor. The Cone-FBG-AE sensor has great application value in the fields of health monitoring, such as aero-engines, microcracks of structural defects.

Design Optimization of Sensitivity-Enhanced Structure for Fiber Bragg Grating Acoustic Emission Sensor Based on Additive Manufacturing.

A four-loop shaped structure of fiber Bragg grating (FBG) acoustic emission (AE) sensor based on additive manufacturing (AM) technology is proposed in the letter. The finite element analysis (FEA) method was used to model and analyze the sensor structure. We aimed at improving the sensitivity, the static load analysis, and the dynamic response analysis of the normal FBG acoustic emission sensor and the FBG AE sensor with improved structure parameters. We constructed the FBG AE sensor experimental system based on a narrowband laser demodulation method and test on real acoustic emission signals. The results demonstrated that the response sensitivity of the FBG acoustic emission sensor was 1.47 times higher than the sensitivity of the normal FBG sensor. The sensitivity coefficient of PLA-AE-FBG2 sensor was 3.057, and that of PLA-AE-FBG1 was 2.0702. Through structural design and parameter optimization, the sensitivity and stability of the FBG AE sensor are improved. The four-loop shaped sensor is more suitable for the health monitoring in fields such as aero-engine blade, micro-crack of structure, and crack growth in bonded joints. While ensuring the sensing characteristics, sensitivity, and stability of the four-loop shaped sensor have been enhanced. It is possible to apply the FBG AE sensor in some complex engineering environments.

Fibre Bragg Grating Based Acoustic Emission Measurement System for Structural Health Monitoring Applications.

Fiber Bragg grating (FBG)-based acoustic emission (AE) detection and monitoring is considered as a potential and emerging technology for structural health monitoring (SHM) applications. In this paper, an overview of the FBG-based AE monitoring system is presented, and various technologies and methods used for FBG AE interrogation systems are reviewed and discussed. Various commercial FBG AE sensing systems, SHM applications of FBG AE monitoring, and market potential and recent trends are also discussed.

Cold Crack Monitoring and Localization in Welding Using Fiber Bragg Grating Sensors

A study on the design, framework, experimental arrangement, data acquisition, and subsequent analysis of cold crack detection using fiber Bragg grating (FBG) sensors during welding is presented. Cold crack induced acoustic emission (AE) events are detected by multiple FBG sensor configurations and using a commercial FBG AE interrogation system. The crack locations are theoretically predicted using a method of linear localization based on the differences in the time of arrival of the AE events at different FBG sensors. The approach is experimentally validated by employing packaged and unpackaged FBG sensor arrays in a welding experiment with gas tungsten arc welding on ultrahigh toughness high hardness armor steel. Frequency analysis of the AE events is also carried out to understand the cold crack characteristics. The weld region of the steel plate is diced into 1-mm cross-sectional pieces, and the positions of the cold cracks are identified using scanning electron microscope imaging and then cross correlated with the measured AE events, and thereby confirming the correct identification of cold crack location using the FBG sensing method.

Application of Fiber Bragg Grating Acoustic Emission Sensors in Thin Polymer-Bonded Explosives.

Fiber Bragg grating (FBG) acoustic emission (AE) sensors have been used in many applications. In this paper, based on an FBG AE sensor, the sensing principle of the interaction between the AE wave and the sensor is introduced. Then, the directionality of the FBG AE sensor on the surface of a thin polymer-bonded explosive (PBX) material is studied. Finally, the time coefficient location method is proposed to correct the AE time detected by the FBG AE sensor, thereby improving the accuracy of location experiments.

Development of high temperature acoustic emission sensing system using fiber Bragg grating

In some applications in structural health monitoring (SHM), the acoustic emission (AE) detection technology is used in the high temperature environment. In this paper, a high-temperature-resistant AE sensing system is developed based on the fiber Bragg grating (FBG) sensor. A novel high temperature FBG AE sensor is designed with a high signal-to-noise ratio (SNR) compared with the traditional FBG AE sensor. The output responses of the designed sensors with different sensing fiber lengths also are investigated both theoretically and experimentally. Excellent AE detection results are obtained using the proposed FBG AE sensing system over a temperature range from 25 ℃ to 200 ℃. The experimental results indicate that this FBG AE sensing system can well meet the application requirement in AE detecting areas at high temperature.

Research on Fiber Bragg Grating Acoustic Emission Technology Applied in Helicopter Bearing Detection

Fiber bragg grating acoustic emission technology can be applied in bearing detection against on the issue of existing nondestructive testing for helicopter structural components mostly not realizing in-situ on-line monitoring. Description of Fiber grating acoustic emission detection principle, with the strengths and weaknesses of fiber bragg grating sensor; detailed analysis of fault mechanism and frequency of helicopter bearing, and study of the resonance demodulation algorithm for signal post-processing; proposing a case of bearing on-line detection compared with other detection technologies against consistent analysis result.