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

High-Resolution Fibre Bragg Grating (FBG) Pressure Transducer for Low-Pressure Detection

Fibre Bragg grating (FBG) pressure sensor has shown great potential in replacing the conventional electrical pressure sensor due to its adaptability to the harsh environment. However, increasing its resolution for low-pressure measurement is still a challenge. In this work, the bonding of FBG to a rubber-based diaphragm pressure transducer was proposed. The proposed pressure transducer had enhanced the sensitivity to 117.7 pm/kPa across the range of 40 kPa, which corresponded to the pressure resolution of 0.008 kPa. Furthermore, the proposed pressure transducer possessed a reference FBG for temperature compensation, where the overall temperature effect was less than 1%

A Study Of Fiber Bragg Grating Temperature Sensor For Under Water Temperature Monitoring

Fiber Bragg grating (FBG) sensors have been widely utilized as a sensor for measuring strain, temperature, and vibration measurements. In this study, an optical FBG sensor system was developed to monitor the temperature fluctuation in water. The sensor was delicately packaged to eliminate the influence of strain acting on the sensor. The sensor had been submerged in iced water and the temperature was constantly increased by using an electric immersion heater. The experimental data were obtained to determine the temperature sensitivity of the FBG sensor. It is found that the relationship between the changes in temperature and changes in Bragg wavelength is virtually higher in linearity with R2 = 0.9997 and has superior sensitivity which is 10.13 pm/°C. This finding proves that the FBG sensor could be a good candidate for temperature-sensing device

Invisibility and indistinguishability in structural damage tomography

Structural damage tomography (SDT) uses full-field or distributed measurements collected from sensors or self-sensing materials to reconstruct quantitative images of potential damage in structures, such as civil structures, automobiles, aircraft, etc. In approximately the past ten years, SDT has increased in popularity due to significant gains in computing power, improvements in sensor quality, and increases in measurement device sensitivity. Nonetheless, from a mathematical standpoint, SDT remains challenging because the reconstruction problems are usually nonlinear and ill-posed. Inasmuch, the ability to reliably reconstruct or detect damage using SDT is seldom guaranteed due to factors such as noise, modeling errors, low sensor quality, and more. As such, damage processes may be rendered invisible due to data indistinguishability. In this paper we identify and address key physical, mathematical, and practical factors that may result in invisible structural damage. Demonstrations of damage invisibility and data indistinguishability in SDT are provided using experimental data generated from a damaged reinforced concrete beam