Application Of Fiber Bragg Grating Sensors 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.

"DISCRIMINATION OF TEMPERATURE AND STRAIN INTERFERENCE IN FBG SENSORS USING TAPERED OPTICAL FIBER SENSOR "

"The optical fiber industry has progressed a lot in recent years. Earlier, they were used as a bed to carry light and image for medical applications, especially in endoscopy. In the mid-1960s, calls were widely used to transmit information. So far, optical fiber technology has been a worthy subject for research. Low loss rate, high bandwidth, electromagnetic reliability, small size, light weight, safety, relatively cheap price, low need for reconstruction and maintenance are the reasons for the attractiveness of optical fibers. In recent years, optical sensors, including FBG, are widely used in the field. Different methods have been used. Among these applications, we can refer to imaging in the fields of civil engineering, aerospace, marine sciences, oil and gas, composites and smart structures. Fiber Bragg Grating (FBG) sensors have found more usages in the industry to diagnose the safety of mechanical structures due to their high sensitivity, non-exposure to the electromagnetic field, linearity, and lightness. A limitation of the application of FBG sensors is the Inability to distinguish the effects of temperature and strain in the simultaneous measurement. For this purpose, we must somehow discriminate the effect of temperature from the strain. In this Article, by designing a tapered fiber-FBG composite sensor we have provided a solution for this problem. Studies performed on the designed composite sensor show that no sensitivity interference will occur in the sensor. In the composite sensor, a tapered fiber optic sensor with a temperature sensitivity of and a FBG sensor with the temperature and strain sensitivity of and, respectively, are used. Keywords: Tapered fiber, Temperature sensor, FBG sensor, Strain health monitor, Structural health monitor, Interferences. "

Distributed Optical Fiber Sensing and Applications Based on Large-Scale Fiber Bragg Grating Array: Review

To achieve data-driven intelligence in engineering applications, the key requirements for distributed optical fiber sensor networks are large capacity, long distance, dense distribution, fast response, and high signal-to-noise ratio (SNR). Combining the traditional optical reflectometry techniques with the large-scale fiber Bragg grating (FBG) array fabricated on-line by a fiber drawing tower, multiplexing and demodulation of thousands of FBG sensors is successfully demonstrated, which greatly expands the application of FBG sensors to the field of distributed sensing. In this work, the fabrication, demodulation, and applications of large-scale FBG arrays are reviewed. Firstly, the on-line fabrication technology and process of large-scale FBG arrays are introduced. Secondly, the demodulation techniques including wavelength demodulation based on optical time-domain reflectometry (OTDR) and optical frequency-domain reflectometry (OFDR), as well as phase demodulation based on phase-sensitive OTDR are reviewed, where we mainly focus on the key parameters such as multiplexing capacity, demodulation speed, spatial resolution, and SNR. Last, the applications of the large-scale FBG arrays are briefly discussed.

Theoretical modeling and simulation of fiber Bragg grating sensor interrogator based on linear variable filter.

With the increasing frequency of aviation accidents in recent years, aircraft safety has received increasing attention. Aircraft operating condition detection is an important part of aviation safety. Fiber Bragg grating (FBG) sensors, with their excellent characteristics, enable online monitoring of aircraft operating conditions. However, the application of FBG sensors in aviation is currently limited because it is difficult for FBG sensor interrogators to meet the requirements of small size, light weight, and good vibration resistance in the aviation field. Therefore, this paper proposes a linear variable filter (LVF)-based FBG sensor interrogator to meet the requirements. An optical model of the interrogator is established. The parameters which determine the performances of the interrogator are analyzed and the design criteria are discussed. According to the requirements in the aviation field, the optical system of the interrogator is designed. The simulation results show that the LVF-based FBG sensor interrogation system has a bandwidth range of 90 nm (1505 nm-1595 nm), a resolution of 2 pm, and a capacity of 15 FBG sensors.

Application of FBG Sensor to Safety Monitoring of Mine Shaft Lining Structure.

The use of fiber Bragg grating (FBG) sensors is proposed to solve the technical problem of poor sensor stability in the long-term safety monitoring of shaft lining structures. The auxiliary shaft of the Zhuxianzhuang coal mine was considered as the engineering background, and a test system implementing FBG sensors was established to monitor the long-term safety of the shaft lining structure. Indoor simulation testing revealed that the coefficient of determination (r2) between the test curves of the FBG sensor and the resistance strain gauge is greater than 0.99 in both the transverse and vertical strains. Therefore, the FBG sensor and resistance strain gauge test values are similar, and the error is small. The early warning value was obtained by calculation, according to the specific engineering geological conditions and shaft lining structure. The monitoring data obtained for the shaft lining at three test levels over more than three years reveal that the measured vertical strain value is less than the warning value, indicating that the shaft lining structure is currently in a safe state. The analysis of the monitoring data reveals that the vertical strain increment caused by the vertical additional force is approximately 0.0752 με/d. As the mine drainage progresses, the increasing vertical additional force acting on the shaft lining will compromise the safety of the shaft lining structure. Therefore, the monitoring must be enhanced to facilitate decision-making for safe shaft operation.

Analysis and Study of FBG Sensor in Crack Monitoring of Aircraft Structure

Based on the FBG sensing principle, the stress of each test point was measured by fatigue test with the change of tensile time using the strain sensitivity characteristics of FBG (fiber Bragg grating) sensor, and the experimental results were compared with the fatigue theory, FBG sensor can not only monitor the various stages of the crack growth, but also can effectively determine the time of occurrence of fatigue cracks and the top of the general location. This will provide a strong basis for the further application of FBG sensors in aircraft structural health monitoring.

Soil–Geogrid Interaction at Various Influencing Factors by Pullout Tests with Applications of FBG Sensors

The behavior of soil–geogrid interaction is a dominant factor in the long-term performance of geogrid-reinforced earth structures. This study investigates the interaction of sandy soil and the embedded geogrid by pullout tests with the application of a novel testing method using fiber Bragg grating (FBG) sensors. Three influencing parameters are considered: dry density of soil, initial normal stress, and fixing condition of the pullout back end. A displacement-controlled mode is used for the normal stress, and the pullout load is applied at a constant loading rate. The results indicate that for the case with a free back end, the peak shear stress mobilizes from the front face toward the back end with the elongation of the geogrid during the pullout process, before the entire slippage of the geogrid. With higher dry density or higher initial normal stress, the mobilization of the peak shear stress transmits more slowly and the distribution area of shear stress along the geogrid is accordingly narrower due to the corresponding higher resistance by the soil particles. However, the values of the peak shear stress in these two cases are still higher than in cases with lower dry density or lower initial normal stress. By contrast, a different distribution mode of shear stress along the soil–geogrid interface is identified for geogrid with a fixed back end, with maximum shear stress developing near the front face for all pullout displacements.

Wavelength-shifted chirped FBGs for temperature compensated strain measurement

Fiber Bragg grating (FBG) is the most researched and implemented sensor of all the available fiber optic sensors till date. Despite being highly sensitive and accurate, the applications of FBG sensors are limited. The main reasons for their limited applications are the high cost and bulkiness of the interrogation system, optical spectrum analyzer (OSA). In this paper, a wavelength shifted chirped FBG (CFBG) interrogation system is presented. It is an optical intensity based FBG interrogation system which can measure positive/negative strain and temperature changes simultaneously. This system is simple, cost effective, and compact with a strain resolution of around 1με. A chirp bandwidth of 5nm can easily provide a strain measurement range of about ±4000με. Essentially, this sensor design abrogates the need for OSA and makes FBG more suitable for field applications.

Strain Transfer Analysis of Embedded Fiber Bragg Grating Strain Sensor

Abstract Due to the difference in the physical and mechanical properties between the optical fiber, protective layer, adhesive layer, and the host material, the strains measured by a fiber Bragg grating (FBG) sensor may not be the actual strains of the host material, which impedes the reliable applications of FBG sensors. To overcome this problem, in this paper, the strain transfer formula was derived by using elastic analysis, the shear-lag method, and several reasonable assumptions taking into account temperature variations and nonaxial stresses, which was an improvement to an existing study (Li, H. N., Zhou, G. D., Ren, L., and Li, D. S., “Strain Transfer Analysis of Embedded Fiber Bragg Grating Sensor Under Nonaxial Stress,” Optic. Eng., Vol. 46, No. 5, 2007, 054402). The analytical results were validated by simulating the behavior of a bare optical fiber through finite element analysis. The data enabled the identification of the parameters that influence the strain transfer from the host material to the embedded FBG sensors and the impact of the temperature variation and sensor alignment angle on the measurement accuracy. This work provided additional knowledge for the improvement of the existing strain transfer theory of FBG sensors in order to achieve a more accurate strain measurement with this sensing technology.

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.

Mechanical Properties of Composites with Embedded FBG Sensors in Manufacturing Engineering

FBG (fiber Bragg grating) sensors are appropriate for embedding in composites manufacturing engineering. Influence of embedding FBG sensors on the composites tension, compression, CAI properties was studied in this paper. Results identified that the mechanical properties decreased obviously when a certain volume content of optical fibers embedded. FBG sensor permits the continuous monitoring of the host material when embedded in the middle 0 degree layer, consistent with strain gauges. Sensitivity coefficient of FBG sensor embedded is almost the same as that not embedded. It offers important reference value on the application of FBG sensors in aerospace composites.

FBG Sensor Technology to Interfacial Strain Measurement in CFRP-Strengthened Concrete Beam

Fiber-reinforced polymer (FRP) composite materials are very attractive for use in strengthening of civil engineering structures because of their high strength to weight and stiffness to weight ratios, being corrosion free, light weight, and potentially high durability. The requirement for any embedded sensor for monitoring strain in FRP-strengthened concrete structures is that the sensor should not be detrimental to the operational requirement of the strengthened structure. Owing to the compatibility with FRP materials, fiber Bragg grating (FBG) sensor is a good choice for embedding at the interface of the FRP-strengthened concrete structures. As the FBG sensors are more flexible and small size (diameter = 250 μm), it may be easily instrumented at the FRP–concrete interface with sufficient surface preparation and suitable adhesive. This article deals with the issues/methods in application of FBG sensors for interfacial strain measurement of reinforced concrete beams strengthened with carbon fiber-reinforced polymer (CFRP). It also describes the experimental studies which were carried out to identify the initiation and propagation of debonding of CFRP from concrete surface using FBG array sensors.

Application of high-speed fiber bragg grating sensing system for safety monitoring of modern ships

Structural health monitoring (SHM) can be understood as the integration of sensing intelligence and possibly also actuation devices to allow the structure loading and damaging conditions to be recorded, analyzed, localized and predicated. SHM sensing requirements are very well suited for fiber optic technology. The fiber Bragg grating (FBG) sensor is a promising sensor of SHM for many applications because of its good optical properties, small size, low insertion loss, antiRF, anti-electromagnetic interference, breakdown voltage, radiation-resistant, light weight, small and large signal bandwidth. There also are reports of the application of FBG sensors for SHM of large industrial and civil works such as dams, bridges [1−2] , aero plane [3] , and tunnels [4,5] . The development of ship’s SHM takes advantage of multidisciplinary work that is being done, and most of the applications reported are about ship hull monitoring systems [6,7] . Previous studies mostly focus on the measurement of static stress [8] . For a modern ship, the thruster is a key part of the propulsion machinery, and the stability of its related equipments has a great influence on the propulsion efficiency of the ship. Electric resistance strain sensors are difficult to be used for the stress measurement for the thruster because of the electromagnetic disturbance and other complicated environment. Low-speed FBG sensors cannot meet the requirements due to the propulsion machinery’s 100 Hz arising vibration frequency. The high-speed FBG sensing system can be used to measure dynamic stress and achieve the goal of safety monitoring in advanced ships. In this letter, the application of a high-speed FBG sensing system for SHM of modern ships is proposed. We apply this sensing system to give on-site tests to an advanced ship. Strain distribution of the bases and supporting frames of its large turbine thrusters are measured both onshore and in the sea when it runs at different work conditions. The maximum natural frequency of this measured structure is 335 Hz. To test all the monitoring points synchronously, an 8-channel senor system is applied, and the data acquisition frequency was 1000 Hz. Most monitoring points are set with single-line sensors for unilateral stress, and the others are set with triple directions sensors to measure shear stress. Temperature compensation is taken with additional FBGs to eliminate the effect of cross-sensitivity between temperature and strain on FBG sensors. As for every single monitoring point, the max and average stress-gas turbine power factor (GTPF): N/Ne curves are analyzed. Then we synthesize all the results from three-time onshore tests and acquire the static stress-GTPF curves. Results from the test at sea are discussed together, thus we can accomplish completely prediction of the dynamic stress-GTPF curve when we did not obtain dynamic data in every work condition because of some objective reason. We examine the vibration amplitude of the wave length of signal light from each specific monitoring point under the same work condition for all tests and find it barely affected by the environment factors, unlike the absolute wave length. Those experimental results are accordant with mechanical theories, and the final reports have obtained clients’ approval. FBGs are periodic alterations in the index of refraction of the fiber core, and only the specified wavelength (Bragg wavelength) related to its grating period is reflected for an input light wave form a broadband source.

Review of fiber Bragg grating sensor technology

The current status of the fiber Bragg grating (FBG) sensor technology was reviewed. Owing to their salient advantages, including immunity to electromagnetic interference, lightweight, compact size, high sensitivity, large operation bandwidth, and ideal multiplexing capability, FBG sensors have attracted considerable interest in the past three decades. Among these sensing physical quantities, temperature and strain are the most widely investigated ones. In this paper, the sensing principle of FBG sensors was briefly introduced first. Then, we reviewed the status of research and applications of FBG sensors. As very important for industrial applications, multiplexing and networking of FBG sensors had been introduced briefly. Moreover, as a key technology, the wavelength interrogation methods were also reviewed carefully. Finally, we analyzed the problems encountered in engineering applications and gave a general review on the development of interrogation methods of FBG sensor.

Multi-Functional Measurement Using a Single FBG Sensor

This paper describes the measurement of average strain, strain distribution and vibration of a cantilever beam made of Carbon Fiber Reinforced Plastics (CFRP), using a single Fibre Bragg Grating (FBG) sensor mounted on the beam surface. Average strain is determined from the displacement of the peak wavelength of reflected spectrum from the FBG sensor. Two unstrained reference FBG sensors were used to compensate for temperature drift. Measured strains agree with those measured by a resistance foil strain gauge attached to the sample. Stress distributions are measured by monitoring the variation in the full width at half maximum (FWHM) values of the reflected spectrum, using a proposed optical analytical model, described in the paper. FWHM values were measured for both the cantilever test beam and for a reference beam, loaded using a four-point bending rig. The trend of the stress distribution for the test beam matches with our analytical model, however with a relatively large noise present in the experimentally determined data. The vibration of a cantilever beam was measured by temporal analysis of the peak reflection wavelength. This technique is very stable as measurements are not affected by variations in the signal amplitude. Finally an application of FBG sensors for damage detection of CFRP plates, by measuring the natural frequency, is demonstrated. With small defects of different sizes applied to the CFRP plate, the natural frequency decreased with damage size.

Real-time monitoring of transverse thermal strain of carbon fiber reinforced composites under long-term space environment using fiber optic sensors

Composites are promising alternatives for space structures because of their versatile characteristics such as high specific stiffness and strength. When composite structures are exposed to the space environments (low Earth orbit, LEO), however, they are known to undergo considerable temperature change induced by the direct sunlight and the Earth's shadow in addition to ultraviolet, high vacuum, atomic oxygen and so forth. Therefore, for the successful completion of their missions, it is important for the structures to maintain the consistent dimensional stability in such a thermal cycling condition. The coefficient of thermal expansion (CTE) of the structures is suitable to express the dimensional stability, and it is needed to be monitored throughout the mission. For this purpose, fiber optic sensors, which have many advantages, were investigated to check their suitability in this paper. Two fiber Bragg grating (FBG) sensors have been adopted for the simultaneous measurement of thermal strain and temperature to get the CTE change of a carbon/epoxy composite laminate. LEO conditions with high vacuum, ultraviolet and thermal cycling environments were simulated in a thermal vacuum chamber. As a pre-test, a FBG temperature sensor was calibrated and a FBG strain sensor was evaluated through the comparison with the electric strain gauge (ESG) attached on an aluminum specimen in the same temperature range as the thermal cycling. The change of the transverse CTE in a composite laminate exposed to the space environment was measured for intervals of aging cycles in real time. As a whole, there was no abrupt change of the CTE after 1000 aging cycles. After aging, however, the CTE decreased a little all over the test temperature range. These changes are thought to have been caused by outgassing, moisture desorption, matrix cracking, etc. In this paper, embedding application of FBG sensors to composites operated under space environment and their successful real-time monitoring of thermal deformations over a long time was shown.

Counting wavelength demodulation of FBG sensors

Measuring amplitude of signal is the usual method in wavelength demodulation of fiber Bragg grating (FBG) sensors recently. This method is easy to be disturbed and has low precision. In this paper, a novel counting wavelength demodulation scheme of FBG sensors using a high birefringent fiber (HBF) loop mirror is reported. This demodulator has simple structure, high precision, cheap price and convenient use. The resolution of the loop mirror device with a HBF of 30 meters long is 0.067 nm. For a center wavelength of FBG of about 1550 nm and a 40 nm shift range of its reflection wavelength, the relative error of measurement is only ± 0.001. This wavelength demodulation device has significance for widespread application of FBG sensors.

1202 機能性繊維のアルミニウムマトリックスへの埋め込み

This paper describes embedment of a FBG (Fiber Bragg Grating) sensor in an aluminum matrix for health monitoring of aluminum based composites as a new application of FBG sensor in the field of structural materials. As FBG sensors are not handled at high temperatures, high temperature stability of them was investigated to select a method of embedding them in aluminum matrix. Taking the results into consideration, a FBG sensor was successfully embedded in aluminum by the interphase forming/bonding method using copper insert. The aluminum specimen was tensile tested under monitoring the peak shift of wavelength of the reflected light from the embedded FBG sensor, and the results showed that it has a possibility to work as a strain sensor in aluminum matrix.