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.
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.
In this study, cotton fabric and coconut shell were integrated in particleboard to reduce the use of wood. Particleboards containing mixed rubberwood and coconut shell with an equal weight ratio have been integrated with various layers of cotton fabric. These materials were bonded by urea formaldehyde with a content level of 12% by weight. Flexural and water absorption tests were conducted to analyze its mechanical properties and dimensional stability. Results of flexural test showed an increment at least double strength values in fabricated materials as compared to control sample. The existence of fabric in the particleboard system also improved the dimensional stability of the produced material. Enhancement of at least 39% of water absorption could help the dimensional stability of the produced material. Overall, these new particleboards showed better results with the incorporation of cotton fabric layers and this study provided better understanding on mechanical and physical properties of the fabricated particleboard.
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.
This paper discusses the use of Fibre Bragg grating sensors (FBG) in structural health monitoring (SHM) of Fibre
reinforced polymer (FRP) aerospace structures. The diminutive sensor provided the capability of embedding inside FRP
structures in order to monitor vital potential locations for damage. Some practical problems associate with manufacturing
process of FRP with embedded FBG sensors, interrelation of distortion to FBG spectra with damage, and interpretation
of FBG spectral responses for identifying the damage will be discussed.
The transmitted spectrums of conventional FBG sensors operating in near infrared region (Bragg wavelength ~ 830nm)
embedded in E-Glass/Vinylester composite sample were investigated at static and after fatigue loading. Also
transmitted waveforms of a FBG attached to a surface of single layer E-Glass/Vinylester composite sample which has
a purposely created hole closer to attached FBG sensor were examined in order to understand the FBG response in a
vicinity of a void/damage, under static loading situation. As a consequence, some conclusions were made on the
sensitivity and durability of the use of FBG sensors fabricated by conventional writing techniques in long term health
monitoring system of composite structures.
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