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A new damage feature index is presented for the structural health monitoring based on Hilbert-Huang transform (HHT). The energy marginal spectrum of the dynamic signal is used to construct damage characteristic parameter, which can reflect the signal energy variation and benefit the structural damage detection. A sinusoidal wave with frequency change and a composite plate vibration experiment with pre-defined damage are designed to verify the effectiveness of characteristic parameter in damage detection. Results obtained from simulation and test show that the extracted non-model-based damage feature index is available and sensitive in damage detection of time-varying system., Peer Reviewed

Modern aerospace, automotive, marine, mechanical and civil structures rely on advanced composites for their added benefits over conventional metallic structures. The complex damage process in composites involves a variety of failure modes, such as matrix cracking, fibre-matrix debonding, fibre fracture and delamination. In structural composites, the initiation of a crack or fracture does not indicate a catastrophic failure. A stable crack propagation stage associated with a steady increase in external load precedes catastrophic failure. Further, due to the alignment of the fibres to the load path, some designs exhibit reserve strength after crack formation, increasing until final collapse. The design and assessment of such structures require adequate consideration of strength and fracture behaviour. An accurate prediction of static collapse behaviour for marine structures is essential for assessing the reserve strength and likelihood of damage. This thesis attempts to gain an insight into the complex stress distribution and numerically model the secondary reserve strength of structures.The issue of frequent keel failures of yachts made out of marine composites is a mystery to many boat builders and designers and the past two decades have seen a number of casualties and material loss. The main thrust of this study was to identify the key variables responsible for these keel failures and to understand the out-of-plane load transfer in Top-hat-stiffeners (THS). This research investigates the damage mechanisms of curved composite structures (L-bends and THSs) and estimates the residual strength after the initial failure. This is vital in estimating the time required to obtain assistance before the boat capsizes.Experimental and numerical investigations are carried out to understand the out-of-plane load transfer in the THS. Specimens were manufactured by hand-layup and vacuum-infused process, and tested until final collapse. Acoustic-emission, embedded optical-fibre sen

Structural Health Monitoring (SHM) is a topic of great interest in structural engineering due to the ageing of the built infrastructures and the growing use of innovative structural systems and construction materials. Although several sensing technologies have been developed for use in SHM systems, fiber optic sensors, especially Fiber Bragg grating sensors (FBGs), are now attracting much attention due to their advantages over other types of sensors. This paper presents a new FBG strain sensor with an unsymmetrical packaging configuration designed to be fixed to the surface of the monitored structure. A 3D Finite Element numerical analysis of the sensor, packaging and adhesive used to fix the system to the host structure was conducted to study the influence of (1) the thickness and mechanical properties of the adhesive, and (2) the configuration of the packaging on the accuracy of the sensor. The results obtained from the numerical models show that the strains measured by the proposed system and the actual strains in the host structure differ by less than 2.5% due to the fact that the packaging contains only one layer of composite material in an unsymmetrical configuration. The proposed design can thus be said to be an improvement compared to the typical configurations of optical fiber surface strain sensors. © 2010 Elsevier Ltd.

Structural Health Monitoring (SHM) is a topic of great interest in structural engineering due to the ageing of the built infrastructures and the growing use of innovative structural systems and construction materials. Although several sensing technologies have been developed for use in SHM systems, fiber optic sensors, especially Fiber Bragg grating sensors (FBGs), are now attracting much attention due to their advantages over other types of sensors. This paper presents a new FBG strain sensor with an unsymmetrical packaging configuration designed to be fixed to the surface of the monitored structure. A 3D Finite Element numerical analysis of the sensor, packaging and adhesive used to fix the system to the host structure was conducted to study the influence of (1) the thickness and mechanical properties of the adhesive, and (2) the configuration of the packaging on the accuracy of the sensor. The results obtained from the numerical models show that the strains measured by the proposed system and the actual strains in the host structure differ by less than 2.5% due to the fact that the packaging contains only one layer of composite material in an unsymmetrical configuration. The proposed design can thus be said to be an improvement compared to the typical configurations of optical fiber surface strain sensors. © 2010 Elsevier Ltd.

Fiber Bragg grating (FBG) sensor technology has been attracting substantial industrial interests for the last decade. FBG sensors have seen increasing acceptance and widespread use for structural sensing and health monitoring applications in composites, civil engineering, aerospace, marine, oil & gas, and smart structures. One transportation system that has been benefitted tremendously from this technology is railways, where it is of the utmost importance to understand the structural and operating conditions of rails as well as that of freight and passenger service cars to ensure safe and reliable operation. Fiberoptic sensors, mostly in the form of FBGs, offer various important characteristics, such as EMI/RFI immunity, multiplexing capability, and very long-range interrogation (up to 230 km between FBGs and measurement unit), over the conventional electrical sensors for the distinctive operational conditions in railways. FBG sensors are unique from other types of fiber-optic sensors as the measured information is wavelength-encoded, which provides self-referencing and renders their signals less susceptible to intensity fluctuations. In addition, FBGs are reflective sensors that can be interrogated from either end, providing redundancy to FBG sensing networks. These two unique features are particularly important for the railway industry where safe and reliable operations are the major concerns. Furthermore, FBGs are very versatile and transducers based on FBGs can be designed to measure a wide range of parameters such as acceleration and inclination. Consequently, a single interrogator can deal with a large number of FBG sensors to measure a multitude of parameters at different locations that spans over a large area.

In this letter, we present results for the spatial performance of a fiber Bragg grating (FBG) sensor to continuous-wave acousto-ultrasonic (AU) signals. The FBG AU sensor is an intensity sensor, using a transmit reflect detection system. The AU sensor was used to receive actively generated continuous-wave ultrasonic signals from a PZT transducer. We present results showing the received signal strength as a function of longitudinal, lateral, and angular separation in small aluminum panels. Measurements were taken for distances of less then 100 mm and at angles from 0 to 90 degrees between the sensor and the transducer. These results show no direct dependence between the received signal strength and the spatial separation, in the range considered. Only variations due to interference were observed.

In this letter, we present results for the spatial performance of a fiber Bragg grating (FBG) sensor to continuous-wave acousto-ultrasonic (AU) signals. The FBG AU sensor is an intensity sensor, using a transmit reflect detection system. The AU sensor was used to receive actively generated continuous-wave ultrasonic signals from a PZT transducer. We present results showing the received signal strength as a function of longitudinal, lateral, and angular separation in small aluminum panels. Measurements were taken for distances of less then 100 mm and at angles from 0 to 90 degrees between the sensor and the transducer. These results show no direct dependence between the received signal strength and the spatial separation, in the range considered. Only variations due to interference were observed.

Baccini, D., Hinckley, S., Canning, J., Cook, K., Allwood, G., Wild, G., ... & Banos, C. (2019, December). Gamma irradiation response in photonic crystal and standard optical fiber Bragg grating sensors for radiation dosimetry. In AOS Australian Conference on Optical Fibre Technology (ACOFT) and Australian Conference on Optics, Lasers, and Spectroscopy (ACOLS) 2019. International Society for Optics and Photonics. https://doi.org/10.1117/12.2539904

Allwood, G., Richardson, S., Wild, G., & Hinckley, S. (2019, December). Standardization of FBG sensors in dual-bus fiber networks. In AOS Australian Conference on Optical Fibre Technology (ACOFT) and Australian Conference on Optics, Lasers, and Spectroscopy (ACOLS) 2019. International Society for Optics and Photonics. https://doi.org/10.1117/12.2539903