Fiber Bragg Grating Strain Gauge Research Articles

Sensor-Enhanced Thick Laminated Composite Beams: Manufacturing, Testing, and Numerical Analysis.

This study investigates the manufacturing, testing, and analysis of ultra-thick laminated polymer matrix composite (PMC) beams with the aim of developing high-performance PMC leaf springs for automotive applications. An innovative aspect of this study is the integration of Fiber Bragg Grating (FBG) sensors and thermocouples (TCs) to monitor residual strain and exothermic reactions in composite structures during curing and post-curing manufacturing cycles. Additionally, the Calibration Coefficients (CCs) are calculated using Strain Gauge measurement results under static three-point bending tests. A major part of the study focuses on developing a properly correlated Finite Element (FE) model with large deflection (LD) effects using geometrical nonlinear analysis (GNA) to understand the deformation behavior of ultra thick composite beam (ComBeam) samples, advancing the understanding of large deformation behavior and filling critical research gaps in composite materials. This model will help assess the internal strain distribution, which is verified by correlating data from FBG sensors, Strain Gauges (SGs), and FE analysis. In addition, this research focuses on the application of FBG sensors in structural health monitoring (SHM) in fatigue tests under three-point bending with the support of load-deflection sensors: a new approach for composites at this scale. This study revealed that the fatigue performance of ComBeam samples drastically decreased with increasing displacement ranges, even at the same maximum level, underscoring the potential of FBG sensors to enhance SHM capabilities linked to smart maintenance.

Experimental study on axial compression monitoring of pile foundation based on sensor-enabled piezoelectric geocable

In concealed underground projects, pile foundations may cause severe engineering accidents owing to factors such as construction technology, geological conditions, and material properties. Accordingly, the construction industry has invariably focused on developing high-precision, distributed, and low-cost monitoring and disaster warning methods. Therefore, a new sensing material, sensor-enabled piezoelectric geocable (SPGC), was developed to monitor the deformation and failure of a pile foundation. Three model piles were constructed, and packaging and layout processes for the SPGC sensing material were proposed. Moreover, a fiber Bragg grating (FBG) sensor and resistance strain gauge were installed for comparison. Pile foundation failure and static load tests were performed using a large servo hydraulic press. The monitored effect was evaluated by obtaining the impedance and voltage signals of the SPGC. Pile foundation failure test results show that the mutation of impedance and voltage signals can be used as combined monitoring data, and the electrical signal of the SPGC can be used in three stages of early warning response. These findings ensure that pile foundation damage can be located, damage precursors can be identified, and timely warning can be provided. The static load test results indicate that the SPGC data are in good agreement with the FBG sensor and strain gauge data. The impedance of the SPGC increases linearly with the load. Accordingly, a linear calculation formula relating impedance and strain is derived. The research results are expected to provide a new technical method for pile foundation construction and long-term operation and maintenance monitoring.

Adit deformation prediction based on ICEEMDAN dispersion entropy and LSTM-BP

Changes in the overburden load and dynamic compaction disturb the upper part of the mine’s adit. Some positions of the adit’s surrounding rock are cracked, and the roof, floor, and two sides are deformed to varying degrees. Accurate and effective adit deformation prediction is helpful to the underground safety decision. Considering the accuracy of adit deformation measurement and the complexity of the underground environment, fiber Bragg grating (FBG) advantages are combined for monitoring the adit deformation. The adits’ deformation during coal mining is predicted by combining the improved adaptive noise complete ensemble empirical mode decomposition (ICEEMDAN) and dispersion entropy analysis with the GA-optimized short and long-term memory network and back-propagation neural network (GA-LSTM-BP) prediction model. This study compares the No. 5 FBG strain gauge to seven other prediction models using it as an example. Compared to other comprehensive algorithms, absolute error (MAE), relative error (MSE), and root mean square error (RMSE) decrease by 0.05–3.07, 0.05–26.96, and 0.13–4.53, respectively, and linear regression correlation coefficient (R2) reaches 0.99. This shows that the model has higher accuracy in predicting adit deformation. The model is applied to the No. 3 FBG strain gauge and No. 1 FBG proximity gauge data for verification and comparative analysis. It also indicates that the accuracy of this model for adit deformation prediction is higher than that of other comprehensive ones.

Discussion on pile axial load test methods and their applicability in cold regions

The measurement of pile axial load is of great significance to determining pile foundation design parameters such as skin friction and end bearing capacity and analyzing load transfer mechanisms. Affected by the temperature and ice content of frozen ground, the interface contact relationship between pile foundation and frozen soil is complicated, making pile axial load measurements more uncertain than that in non-frozen ground. Therefore, it is necessary to gain an in-depth understanding of the current pile axial load test methods. Four methods are systematically reviewed: vibrating wire sensors, strain gauges, sliding micrometers, and optical fiber strain sensors. At the same time, the applicability of the four test methods in frozen soil regions is discussed in detail. The first two methods are mature and commonly used. The sliding micrometer is only suitable for short-term measurement. While the Fiber Bragg grating (FBG) strain gauge meets the monitoring requirements, the Brillouin optical time-domain reflectometer (BOTDR) needs further verification. This paper aims to provide a technical reference for selecting and applying different methods in the pile axial load test for the stability study and bearing capacity assessment of pile foundations in cold regions.

Smart Railway Traffic Monitoring Using Fiber Bragg Grating Strain Gauges.

There is today ample evidence that fiber Bragg gratings (FBGs) distributed along a railway track can provide robust axle counting and bring numerous assets compared to competing technologies in this practical environment. This work brings two relevant originalities with respect to the state-of-the-art solutions. First, a study of the strain distribution in the rail cross-section is performed to determine the sensitivity according to the charge and the position on the rail. Secondly, the technology is deployed along the rail track as a smart object where the sensor head is composed of four FBG wavelength-division-multiplexed in a single telecommunication-grade optical fiber and interrogated by a miniaturized read-out device. Two FBGs ensure the detection of the train direction and another two bring the required redundancy to reach a safety integrity level (SIL) 4. The read-out unit has been specifically developed for the application and contains a vertical-cavity surface-emitting laser (VCSEL) and a photodiode driven by a high-speed microprocessor unit that processes the data and communicates the useful information, i.e., the number of axles. On-field tests confirm that the proposed approach makes the installation process easier while it democratizes the technology.

Applications of multi-type fiber Bragg grating sensors in explosion dynamic measurement

The immunity to electromagnetic interference performance of fiber Bragg grating (FBG) is a potential advantage in explosion measurement with electromagnetic pulses. Firstly, with the help of wavelet analysis and contrasting resistance strain gauge, the dynamic response performance of FBG is verified by Split Hopkinson Pressure Bar (SHPB). Then, a concrete explosion-proof model is designed and built. FBG acceleration sensors and FBG strain gauges are arranged on the inner wall of the model to measure dynamic signals during the explosion. The hinge thickness of the FBG acceleration sensor is increased to improve its working frequency. Through the comparative analysis of the test results by various sensors, it’s considered that the FBG sensor has good dynamic response performance at its working frequency. Finally, according to the measurement results and wavelet transformation, the characteristics of blast waves are analyzed by combining with the time domain and frequency domain.

Strain Modal Testing with Fiber Bragg Gratings for Automotive Applications.

Strain Modal Testing (SMT), based on strain sensors signal processing, is an unconventional approach to perform Experimental Modal Analysis which is typically based on data measured by accelerometers. SMT is still mainly restricted to academia and requires additional investigation for a successful transition towards industry. This paper critically reviews why the automotive sector can benefit from this relatively new approach for a variety of reasons. Moreover, a case study representative of the automotive field is analyzed and discussed. Specifically, an SMT methodology is applied to evaluate the modal properties of a reinforced composite roof belonging to a racing solar powered vehicle. In the experimental activity, signals from Fiber Bragg Grating (FBG) sensors, strain gauges, and accelerometers were simultaneously acquired and further processed. The advantages of using optical fibers were discussed, together with their weaknesses and ongoing challenges. The FBG results were compared with the conventional analysis performed with the accelerometers, emphasizing the main similarities and discrepancies.

Strain Sensor’s Network for Low-Velocity Impact Location Estimation on Carbon Reinforced Fiber Plastic Structures: Part-II

Identification of low velocity impact (LVI) location in composite aircraft structures is seamless need for safe, reliable operation and maintenance of aerospace industry. To locate the LVI’s an optimized sensor network has designed using the strain response from fiber Bragg grating (FBG) & resistance strain gauge (RSG) sensor bonded to the composite structure. Strain scan (SS) algorithm has been developed to locate such events reported as Part-I. In this work, we have developed a novel algorithm based on weighted energy (WE) of the sensor response. The LVI’s has been carried out on composite structures & the locations of LVI’s have estimated using SS, WE & previously developed machine learning base support vector machine (SVM) algorithms. The WE and SS algorithms are based on proximity of events (closer to the sensor, higher the response), whereas LS-SVR is a data-driven approach. Further, we have compared the performance of the developed algorithms and algorithms cited in the literature using the performance index (PI), a measure of estimation efficiency as a function of the number of sensors, dimension/area of the structure, error & number of test cases. It is established that WE algorithm shown suprema performance over the other algorithm with 34 mm mean Euclidian distance error & PI value of 5.5.

Abnormal diagnosis of fiber Bragg grating strain gauges in health monitoring system

Abnormal diagnosis of fiber Bragg grating strain gauges in health monitoring system

Strain, natural frequency, damping coefficient and elastic modulus of mortar beams determined by fiber Bragg grating (FBG) sensors

Abstract Structural health monitoring can detect anomalies in time, allowing the implementation of more efficient maintenance and repair actions in special engineering structures. An alternative in the monitoring and evaluation of structures in civil engineering is the use of optical fibers inscribed with Bragg gratings (FBG or Fiber Bragg Grating). This paper aims to compare available techniques to estimate the elastic module of cementitious composites, as well as contribute to the application of optical fiber sensors in the monitoring of strain, natural vibration frequency, damping coefficient and elastic modulus of mortar beams. The FBG sensors manufactured and calibrated by the authors presented a good precision for measuring those parameters in mortar samples. The results show that FBG sensors and strain gauge sensors present a similar result for strain and estimation of the elastic module (static and dynamic), therefore, bare FBGs could be further investigated for non-destructive testing.

Experimental study on three-point bending performance of CFRP shaft embedded FBG sensor

The bending deformation of Carbon Fiber Reinforced Polymer (CFRP) shaft is one of the important indicators reflecting its performance. Monitoring the deformation of CFRP shaft under different loads is of great significance for the optimal design of CFRP shaft. Fiber Bragg Grating (FBG) sensor is small in diameter, easy to be embedded inside the CFRP shaft, which has little influence on the structure itself. In addition, it can realize "one fiber multi-point" measurement, which is very suitable for the internal monitoring of anisotropy composites. This paper proposes a pre-embedded FBG sensor to monitor CFRP shaft strain. Prepared CFRP shaft test piece. Four FBG sensors are embedded inside the shaft, and four FBG sensors and four strain gauges are pasted on the surface of the shaft. The CFRP shaft was subjected to three-point bending loading on a universal testing machine. The strain data obtained by FBG sensor and strain gauge under various loads were compared and analyzed. The feasibility and accuracy of the embedded FBG sensor to monitor CFRP shaft strain were verified.

Dynamic Responses Measured by Optical Fiber Sensor for Structural Health Monitoring

An optical fiber sensing system integrating a fiber Bragg grating (FBG) sensor, a long-period fiber grating (LPFG) optical filter and a photodetector is presented to monitor the dynamic response of a structure subjected to base excitation and impact loading. The FBG sensor is attached to a test specimen and connected to an LPFG filter. As the light reflected from the FBG sensor is transmitted through the long-period fiber grating filter, the intensity of the light is modulated by the wavelength, which is affected by the strain of the FBG. By measuring the intensity of the light using a photodetector, the wavelength reflected from the FBG sensor can be demodulated, thus leading to the determination of the strain in the structure. To demonstrate its effectiveness, the proposed sensing system was employed to measure the dynamic strain of a beam subjected to mechanical testing. The mechanical tests comprised three load scenarios: base excitation by a shaker at resonant frequency, impact loading by a hammer and shock test on a drop table. To monitor the dynamic strain during the test and validate the accuracy of the measurement of the FBG sensor, strain gauge was used as reference. Experimental results show good correlation between the measurements of FBG sensor and strain gauge. The present work provides a fast response and easy-to-implement optical fiber sensing system for structural health monitoring based on real-time dynamic strain measurements.

Ex Vivo Biomechanical Study of Apical Versus Papillary Neochord Anchoring for Mitral Regurgitation

Neochordoplasty is an important repair technique, but optimal anchoring position is unknown. Although typically anchored at papillary muscles, new percutaneous devices anchor the neochordae at or near the ventricular apex, which may have an effect on chordal forces and the long-term durability of the repair. Porcine mitral valves (n= 6) were mounted in a left heart simulator that generates physiologic pressure and flow through the valves, and chordal forces were measured with Fiber Bragg Grating strain gauge sensors. Isolated mitral regurgitation was induced by cutting P2 primary chordae, and the regurgitant valve was repaired with polytetrafluoroethylene neochord with apical anchoring, followed by papillary muscle fixation for comparison. In both situations, the neochord was anchored to a customized force-sensing post positioned to mimic the relevant invivo placement. Echocardiographic and hemodynamic data confirmed that the repairs restored physiologic hemodynamics. Forces on the chordae and neochord were lower for papillary fixation than for the apical fixation (p= 0.003). In addition, the maximum rate of change of force on the chordae and neochordae was higher for apical fixation than for papillary fixation (p= 0.028). Apical neochord anchoring results in effective repair of mitral regurgitation, albeit with somewhat higher forces on the chordae and neochord suture, as well as an increased rate of loading on the neochord compared with the papillary muscle fixation. These results may guide strategies to reduce stresses on neochordae as well as aid optimal patient selection.

Abstract 16974: Experimental Insights Into Transapical Neochordplasty: A Quantitative Examination of Neochord Placement Using an Ex Vivo Left Heart Simulator

Introduction: Neochordoplasty is an important repair technique, though the optimal anchoring position is unknown. While typically anchored at papillary muscles, new percutaneous devices anchor the chordae at or near the ventricular apex, which we hypothesize will result in significantly higher forces on the chordae and neochord. Methods: Porcine mitral valves were dissected (n=3) and mounted in a custom 3D printed left heart simulator generating physiological pressure and flow. Hemodynamic and echocardiographic data were collected, and chordal forces were measured using Fiber Bragg Grating (FBG) strain gauge sensors. Isolated MR was induced by cutting P2 primary chordae resulting in prolapse. Regurgitant valves were then repaired with a PTFE neochord with transapical fixation, followed by papillary fixation for comparison. In both cases, the neochord was anchored to a customized force-sensing post positioned to mimic in vivo placement ( Fig. A ). Results: Hemodynamic and echocardiographic data confirmed that both techniques resulted in elimination of MR in all valves and restoration of physiologic hemodynamics. Peak forces on the chordae and neochord were lower for papillary than the transapical fixation (p=0.04). Force tracings were compiled for each class of chordae at baseline, after prolapse, and after both repair techniques ( Fig. B ). The maximum dF/dt for the neochord suture was 30.6 N/s with the papillary fixation and 51.7 N/s with the transapical fixation. These may translate into increased stress on the mitral valve apparatus. Conclusions: Transapical fixation results in higher peak forces on the chordae and noechord suture as well as an increased rate of loading on the neochord when compared to the papillary muscle fixation and may influence repair durability.

Performance Deterioration of Heavy-Haul Railway Bridges under Fatigue Loading Monitored by a Multisensor System

Heavy-haul railway bridges play an increasingly essential role in the transportation in China due to the increasing transport volume. The performance deterioration of the scale models of a typical heavy-haul railway bridge under fatigue loading is monitored in this work, based on a multisensor system including the fiber-reinforced polymer optical fiber Bragg grating and electrical resistance strain gauges, linear variable displacement transducer, and accelerometer. Specifically, by monitoring/observing on the failure mode, fatigue life, load-midspan deflection response, material strain development, and so forth, this work develops an S-N model by comparing the relationship between fatigue life and rebar stress range with that between fatigue life and load level and proposes a damage evolution model considering the coupling of the stiffness degradation and inelastic deformation of specimens. It is found that the fatigue life of specimens is determined by the fatigue life of the rebar at the bottom and it may be lower than 2.0 million cycles with a 30-ton axle weight when environmental factors are taken into account. The predictions of the models agree well with experimental results. Therefore, this work furthers the understanding of the fatigue performance deterioration of the bridges by using a multisensor system.

Field study of residual forces developed in pre-stressed high-strength concrete (PHC) pipe piles

A large-scale field testing program for the study of residual forces in pre-stressed high-strength concrete (PHC) pipe piles is presented in this paper. Five open-ended PHC pipe piles with 13 or 18 m in embedded length were installed and used for static loading tests at a building site in Hangzhou, China. All the piles were instrumented with fiber Bragg grating (FBG) strain gauges. The residual forces in these piles were recorded during and after installation. The measured load transfer data along a pile during the static loading tests are reported. The effect of the residual force on the interpretation of the load transfer behavior is discussed. The field data show that residual force along the installed pile increases approximately exponentially to the neutral plane and then reduces towards the toe. The residual force decreases with time to a stable value after pile jacking due to the secondary interaction between the pile and the disturbed soil around the pile and other factors. The large residual forces along the PHC pipe piles significantly affect the evaluation of the pile load distributions, and thus the shaft and toe resistances. The conventional bearing capacity theory tends to overestimate the shaft resistance at positions above the neutral plane and underestimate the shaft resistance at positions below the neutral plane, and the toe resistance for an open-ended PHC pipe piles founded in stratified soils.

Laboratory measurements of vortex- and wake-induced vibrations of a tandem arrangement of two flexible risers

The dynamic response of two flexible model risers in tandem arrangement immersed in a stepped current was analyzed. The risers, with an external diameter of 20 mm and a total length of 6200 mm, had an aspect ratio of 310. They were hinged to the support structure at the center-to-center distances away 3-12 times the external diameter. The top 1200 mm was exposed to a uniform current at a speed which was up to 0.9 m/s (the Reynolds number was 18000) and the rest in still water. The dynamic responses, which were obtained through the Fiber Bragg Grating strain gauges mounted on the surface, were analyzed by studying the cross-flow amplitudes and modal weights. The cross-flow vibration were observed up to the third mode, and the modal transformation from the second mode to the third mode was clearly observed. The experiment confirmed that the typical vortex-induced vibration (VIV) had occurred on the up-stream riser. But for the down-stream riser, the main excitation mechanism was wake-induced vibration (WIV). The modal transformation of WIV was more complex than that of VIV, which might be helpful for other researchers to study the interference effect.

Condition Monitoring and Damage Location of Wind Turbine Blades by Frequency Response Transmissibility Analysis

Incipient defects occurring in long wind turbine (WT) blades are difficult to detect using the existing condition monitoring (CM) techniques. To tackle this issue, a new WT blade CM method is studied in this paper with the aid of the concept of transmissibility of frequency response functions. Different from the existing CM techniques that judge the health condition of a blade by interpreting individual CM signals, the proposed method jointly utilizes the CM signals measured by a number of neighboring sensors. This offers the proposed technique a unique capability of both damage detection and location. The proposed technique has been experimentally verified by using the real CM data collected during the fatigue and static tests of a full-scale WT blade. The experiment has shown that the new technique is effective not only in damage detection but also in damage location when either fiber Bragg grating strain gauges or accelerometers are used for data acquisition.

Fabrication of FBG Strain Gauge Used for High Temperature Strain Monitoring

Fiber Bragg Grating (FBG) sensing technology is widely used in detection of temperature, strain and etc. Now the application of FBG sensor is limited below 200°C. Application over 200°C is still an engineering challenge since no suitable FBG strain gauge. In this paper, FBG strain gauge structure which consists of three FBGs is designed and fabricated based on the theoretical strain and stress analysis. This strain gauge can be used for the real-time high temperature strain monitoring situation. The elastic high-temperature alloy (10MoWVNb) is chosen as the substrate. The three FBGs with a similar performance are fabricated on the substrate by high-temperature glue. Among the three FBGs, FBG1 is used for the horizontal strain monitoring, FBG2 is used for the longitudinal strain monitoring, and FGB3 is used for high temperature cross-sensitive compensation. The fabricated high temperature FBG gauge is demonstrated suitable for high temperature strain monitoring by experiment.

Inflow Parameter Effects on Wind Turbine Tower Cyclic Loading

Wind turbine towers are fatigue-critical structures subjected to a variety of atmospheric wind regimes at onshore installations. At a commercial wind farm in Southwestern Ontario, the structural steel supporting tower of a multi-megawatt horizontal-axis turbine has been instrumented with a fiber Bragg grating strain gauge array. A nearby meteorological mast allows wind conditions to be classified on the basis of horizontal turbulence intensity and vertical wind shear. Data has been collected over a measurement campaign spanning multiple months, and a sample of the tower's cyclic loading history has been compiled. Comparisons are drawn between accumulated hourly loading cycle spectra for operation across different upwind inflow parameters.