Modal analysis of high frequency acoustic signal approach for progressive failure monitoring in thin composite plates

During the past few decades, many successful research works have evidently shown remarkable capability of Acoustic Emission (AE) for early damage detection of composite materials. Modal Analysis of AE signals or Modal Acoustic Emission (MAE) offers a better theoretical background for acoustic emission analysis which is necessary to get more qualitative and quantitative result. In this paper, the application of MAE concept in a single channel AE source location detection method for failure characterization and monitoring in thin composite plates was presented. Single channel AE source location is one of the recent studies for composite early damage localization, owing to the growing interest and knowledge of modal analysis of AE wave. A tensile test was conducted for glass fiber epoxy resin specimen with small notch. A single channel of AE system was used to determine the AE source location on specimen under testing. The results revealed that AE single channel source location provides reasonable accuracy for glass fiber laminate which was tested

Development of fibre bragg grating (FBG) based pressure transducer with temperature compensation

In this work, an aluminium diaphragm fibre Bragg grating (FBG) pressure transducer with temperature compensation is been presented. FBG based sensors good for some applications such as pressure vessel, biomedical and combustion chamber. One of the greatest challenges for an FBG based transducer is the inconsistency in output wavelength due to temperature variations. This lead to huge variation pressure readings. In this study, two FBG are bonded on the diaphragm and base surface of the pressure transducer, respectively. The inconsistency of wavelength was eliminated by applying the temperature compensation technique. The result shows that this FBG pressure transducer has a sensitivity of 2.849 nm/MPa and a linear fitting coefficient of 99.97% in a pressure range from 0 to 0.2 MPa. This FBG pressure transducer is proven to be suitable for pressure measurement of gas or liquid with an average error of 1.97%

Review of high sensitivity fibre-optic pressure sensors for low pressure sensing

Fibre Bragg grating (FBG) pressure sensors show a great potential in replacing conventional electrical pressure sensors due to their numerous advantages. However, increasing their pressure sensitivity performance for low hydrostatic pressure measurement is still a challenge. This paper reviewed recent pressure sensitivity enhancement methods that could be divided into two groups, namely intrinsic and extrinsic. For the intrinsic enhancement method, this paper reviewed polymer FBGs, special fibre sensors, interferometric sensors, and special grating sensors. For the extrinsic enhancement method, polymer-based pressure transducers, diaphragm-based pressure transducers, and other structure-based pressure transducers were reviewed in detail

A highly sensitive multiplexed FBG pressure transducer based on natural rubber diaphragm and ultrathin aluminium sheet

Pressure measurement with a good sensitivity has always been a concern in most of the engineering applications and biomedical field. In this paper, a multiplexed FBG bonded on an ultrathin aluminium sheet which act as a cantilever deflected due to a deformation from a natural rubber based diaphragm has been proposed and studied. By using two gratings inscribed on a single optical fibre which senses the positive and negative strain has enhanced the sensitivity of the pressure transducer recorded at 329.56 pm/kPa or corresponding to 10.7893 kPa−1 across the range of 0 to 10 kPa with a good linearity of 99.76%. Furthermore, the thermal cross-sensitivity is compensated

Investigation of low frequency fibre Bragg grating accelerometer based on thermoplastic cantilever beam

Vibration measurement technique is very important in structural integrity monitoring. Various fibre Bragg grating (FBG) based accelerometers have been developed for vibration measurement. However, most of the researchers focused on high frequency monitoring and only few reported works are based on low frequency measurement. Therefore, this paper presented a low frequency FBG accelerometer based on Polyphenylene Ether (PPE) thermoplastic cantilever beam. The proposed FBG accelerometer was attached to a shaker and vibration signals were given with variations in frequency and acceleration. As a result, the FBG accelerometer has a sensitivity of 110 pm/g and natural frequency of 9 Hz. The proposed accelerometer capable to detect low frequency of 2 Hz at 0.04 g which is suitable for utilisation in seismic monitoring of earthquake

Delamination detection in thin-walled composite structures using acoustic pitch-catch technique with Fiber Bragg Grating Sensors.

Structural health monitoring (SHM) of a composite structure is essential in maintaining the integrity of the structure. Over the years, various studies have reported on the use of conventional electrical sensors in analysing acoustic wave propagation for delamination detection. However, electrical sensors are associated with drawbacks such as high signal attenuation, are prone to electromagnetic interference (EMI) and are not suitable for harsh environments. Therefore, this paper reported on the use of fiber Bragg grating (FBG) sensors for delamination detection. Two composite structures with delamination sizes of 10 cm × 2 cm and 10 cm × 6 cm were fabricated. Two FBGs were bonded before and after the delamination. In addition, three trials of impacts were induced at the centre of the structure. Multiple signal parameters were obtained and analysed, which were the time delay, amplitude difference and velocity difference. The experimental results revealed that the time delay, amplitude and velocity analysis varied for both the delamination sizes with an average percentage of 42.36%, 97.09% and 42.39%, respectively. Therefore, it was confirmed that the increase in delamination size resulted in a longer time delay, higher signal amplitude attenuation and slower wave propagatio

An Investigation of Acoustic Emission Signal Attenuation for Monitoring of Progressive Failure in Fiberglass Reinforced Composite Laminates

Glass fiber reinforced polymer (GFRP) laminates have a high damping characteristic which can retard ultra-high frequency guided wave signals from propagating along the plate. Owing to this, the identification of an effective area for sensor location is essential. Appropriate signal processing, including wavelet analysis was done, in order to observe the details of an acoustic emission (AE) signal which was emitted at a distance from it source. This study reveals that it is necessary to consider the near field and far field effects of AE signal attenuation, in particular, to determine a composite's micro failure characterization. Consequently, this attenuation behavior was used to develop the non-velocity based source mapping to monitor the progressive failure in composite laminates. This paper details the outcomes of the signal energy attenuation method with an improved algorithm for progressive failure monitoring in fiberglass reinforced composite laminates and the 'effective length' for better AE detection

Measurement of Dielectric Properties of Low-Density Polyethylene Nanocomposites Using “Sub-Hertz” Dielectric Spectroscopy

Recently, many studies have been conducted on the dielectric properties of Low-Density Polyethylene (LDPE) nanocomposites and produced different results. However, the composition of LDPE polymer and boron nitride (BN) as nanofiller has neither been well understood nor producing a convenient result. Similarly, the dielectric spectroscopy measured at “sub–hertz” frequency has been of little interest among researchers since it is often influenced by “conduction-like” effect. This research identified the dielectric properties of LDPE nanocomposites filled with hexagonal boron nitride (h-BN) nanofillers by using dielectric spectroscopy technique. The dielectric loss and relative permittivity for three different filler concentrations were investigated under “sub-hertz” frequency ranges at room temperature. The cylindrical electrode with guard ring configuration was used to conduct the experiment, in accordance to the ASTM D150 standard. The results revealed that 5 wt% filled polymer has lower loss tangent and permittivity compared to the unfilled polymer, due to the strong interaction between nano-particle and the polymer. This strong interaction is believed to limit the movement of the polymer chain. The decrease in loss tangent also indicates lower quasi-DC at low frequency. However, further increase in the filler loading has recorded an increment in the value of permittivity and loss tangent. This higher effective permittivity is mainly due to the influence of the filler permittivity

Effect of Humidity on Partial Discharge Characteristics of Epoxy/Boron Nitride Nanocomposite under High Voltage Stress

Partial discharge (PD) may lead to the degradation of insulating materials and affect the lifetime of high voltage equipment. This paper describes the effect of relative humidity on PD characteristic of epoxy/boron nitride (BN) nanocomposite under high voltage (HV) stress. In this work, CIGRE Method II was utilized as an electrode configuration. BN nanofiller was chosen because of its high insulating properties with high thermal conductivity. The PD characteristics such as PD charge magnitude, PD number or occurrence, and average of PD charge during certain of ageing time under HV stress against relative humidity were examined. The results revealed that PD number of humid samples is higher about 8~14% compared to the normal ones. It is considered due to the decrease of surface resistance of the humid samples. The PD charge magnitudes of humid samples are slightly higher compared to the normal ones. The epoxy/BN nanocomposite has lesser PD number and magnitude compared to the neat epoxy samples