Structural Health Monitoring Systems based on embedded FBG sensors, to identify damage
conditions, are largely dependent on the spectral distortion of the sensors. The uneven stress gradient
occurring along the grating of FBG sensors, due to damage inside composite structures can be
estimated by analysing significant changes that appear in the FBG response spectra. However, the
stochastic nature of the distorted shape of the FBG spectra makes it difficult to interpret and quantify
the existing damage at the location of the FBG sensors. There are several indexing methods
proposed by researchers. We have previously presented a novel concept of the “Distortion Index
(DI)” which is defined using distorted spectra of FBG sensors. It was observed that the DI increases
with the increase in damage size.
The Distortion Index (DI) is introduced to create a correlation between the damage and the distortion
of the response spectra of a FBG sensor. This index provides the ability to generalise the distortion
of FBG spectra for a particular structure. The index can be used to quantify the damage in the
structure relative to its original condition, which can be the condition of structure during a regulated
time, i.e. a month uninterrupted operation or first hours in operation, of a structure can be used as no
damage condition.
In this paper we discuss the application of distortion index and comparison with available several
other indexes.
Structures can go through harsh environmental adversity and can experience material loss and cracks during their service lives. Infill material is used to ensure a supporting bed for a grouted repair. Epoxy grouts are used for repairing and rehabilitating structures, such as foundations, bridges, piers, transportation pipelines, etc., because they are resistant to typical chemicals and possess superior mechanical properties than other grouts. The resin based infill used inside the void or cracked space of the repair is vulnerable to shrinkage. When these filled grouts have high resin content, cracks can develop from residual stresses, which can affect the load transfer performance. It follows that interlayer separation and cracking of infill layer can occur in a grouted repair. In this study, volumetric shrinkage of two epoxy grouts was measured over 28 days using a Pycnometer. The highest volumetric shrinkage measured after 7 days was found to be 2.72%. The results suggest that the volumetric shrinkage can be reduced to 1.1% after 7 days, through the introduction of a coarse aggregate filler; a 2.5 times reduction in shrinkage. About 98% and 92% of the total shrinkage over the 28 day period, of the unfilled and filled grouts respectively, was found to occur within 7 days of mixing. The gel-time shrinkages were also calculated, to determine the “postgel” part of the curing contraction which subsequently produces residual stresses in the hardened grout systems.
Fibre optic sensors where embedded in an FRP panel during manufacture. Strain data was collected under uniform distributed loading and used to inversely predict distributed loads. A square FRP panel was manufactured while embedding an FBG sensor network. The panel was tested under various uniform distributed loads. Sensor data was collected and a strain signature was developed for each load case. A Finite Element Analysis was used to predict strain data at sensor locations and these were found to correlate well with the experimental values. Software was used to inversely predict distributed loading from the strain data with good accuracy. It was found with FEA and experimentally that the number of sensors could be reduced for this type of loading.
KEYWORDS: Fiber Bragg gratings, Sensors, Wavelets, Near infrared, Denoising, Structural health monitoring, Composites, Discrete wavelet transforms, Signal to noise ratio, Signal processing
During the past decade, many successful studies have evidently shown remarkable capability of Fiber Bragg Gratings (FBG) sensor for dynamic sensing. Most of the research works utilized the 1550 nm wavelength range of FBG sensors. However near infra-red (NIR) FBG sensors can offer the lower cost of Structural health Monitoring (SHM) systems which uses cheaper silicon sources and detectors. Unfortunately, the excessive noise levels that experienced in NIR wavelengths have caused the rejection of sensor that operating in this range of wavelengths for SHM systems. However, with the appropriate use of signal processing tools, these noisy signals can be easily ‘cleaned’. Wavelet analysis is one of the powerful signal processing tools nowadays, not only for time-frequency analysis but also for signal denoising. This present study revealed that the NIR FBG range gave good response to impact signals. Furthermore, these ‘noisy’ signals’ response were successfully filtered using one dimensional wavelet analysis.
Wind energy is seen as a viable alternative energy option for future energy demand. The blades of wind turbines are generally regarded as the most critical component of the wind turbine system. Ultimately, the blades act as the prime mover of the whole system which interacts with the wind flow during the production of energy. During wind turbine operation the wind loading cause the deflection of the wind turbine blade which can be significant and affect the turbine efficiency. Such a deflection in wind blade not only will result in lower performance in electrical power generation but also increase of material degradation due high fatigue life and can significantly shorten the longevity for the wind turbine material. In harnessing stiffness of the blade will contribute massive weight factor and consequently excessive bending moment. To overcome this excessive deflection due to wind loading on the blade, it is feasible to use shape memory alloy (SMA) wires which has ability take the blade back to its optimal operational shape. This paper details analytical and experimental work being carried out to minimize blade flapping deflection using SMA.
We report the use of fiber Bragg grating (FBG) sensors for strain measurement in a rectangular composite-bonded concrete beam. Three FBG sensors are multiplexed by using a frequency-modulated continuous wave technique and embedded at three different locations at the interface between the composite reinforcement and surfaces of the concrete beam specimen. Strain measurements were conducted with the concrete beam specimen subjected to a three-point bending test. The strains measured from the FBG sensors are compared with that from the external bonded electrical strain gauges.
In this paper we report of experimental studies on strain monitoring by using fiber Bragg grating sensors in concrete structures. The strain variation of the specimen under different loading conditions were monitored by the Fiber- optic Bragg grating (FBG) sensors. The FBG sensors have been pre-installed in the structure by embedding either inside the concrete specimen or at the interface between the concrete and the composites. The strain reading from the fiber grating sensor compares favorably with that obtained from the conventional strain gauge in uni-axial compression testing. The test result generally indicated that the concrete structures can be strengthened significantly by wrapping with glassfiber composites. The sensor embedded at the notch tip provides a very good indication of the health condition of the strengthened structure, especially in high stress concentration area. The strain sensitivity by using FBG sensor is 67 (mu) (epsilon) .
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