Accurate structural health monitoring in composites: With fibre Bragg grating sensors

Compared to metals, composite materials offer higher stiffness, more resilience to corrosion, have lighter weights, and their mechanical properties can be tailored by their layup configuration. Despite these features, composite materials are susceptible to a diversity of damages, including matrix cracks, delamination, and fibre breakage. If...

A method for determining the position of FBG sensors accurately

Fibre Bragg grating sensors have gained a lot of attention in damage detection and strain measurement applications in the past few decades. These applications include matrix crack detection and delamination tip monitoring in composite structures, crack detection in concrete and civil engineering structures and etc. The damage localisation...

Evaluation of the mechanical performance of a composite multi-cell tank for cryogenic storage: Part II – Experimental assessment

This study focuses on the understanding of the thermal and structural behavior of an innovative Type IV multi-spherical composite-overwrapped pressure vessel through an experimental assessment that consists of hydrostatic testing at ambient conditions and pressure cycling with a cryogenic medium (LN₂). During hydro-burst testing at...

A Method for Determining the Length of FBG Sensors Accurately

In this letter, we propose a method for estimating the length of single-mode fiber Bragg grating type sensors with high accuracy. Our method is based on calculating the maximum oscillation frequency of the side-lobes of the FBG reflection spectrum. We show that this frequency is independent of the stress field to which the sensor is subjected...

Analysis of FBG reflection spectra under uniform and non-uniform transverse loads

Loads applied transversely on the external surface of waveguides change their circular cross-sectional geometry generating birefringence. Due to this effect the reflected spectrum of a Fibre Bragg grating (FBG) undergoes a splitting of the single peak of the Bragg wavelength. In this work, we employed the Transfer Matrix Method (TMM) for x-...

Characterisation of Transverse Matrix Cracks in Composite Materials Using Fibre Bragg Grating Sensors

In this paper, we propose a novel approach to characterise barely visible transverse matrix cracks in composite structures using fibre Bragg grating (FBG) optical sensors. Matrix cracks are one of the most prevalent types of damage in composite structures, and detecting them in the internal layers of composites has remained a challenge. In...

Design and Experimental Assessment of a Multi-spherical Composite- Overwrapped Pressure Vessel for Cryogenic Storage

In the field of cryogenic storage, the medium inside the pressure vessel is in a liquid state and thus is incompressible. Therefore the storage tank should be designed in a way, that makes the best possible use of the available space within an aircraft. A composite-overwrapped pressure vessel (COPV) based on intersecting spheres (multi-sphere)...

Calculation of the Mean Strain of Smooth Non-uniform Strain Fields Using Conventional FBG Sensors

In the past few decades, fibre Bragg grating (FBG) sensors have gained a lot of attention in the field of distributed point strain measurement. One of the most interesting properties of these sensors is the presumed linear relationship between the strain and the peak wavelength shift of the FBG reflected spectra. However, subjecting sensors to a...

Analysis of FBG reflection spectra under anti-symmetrical strain distributions using the approximated transfer matrix model

In this paper, we used the efficient formulation of the approximated transfer matrix model (ATMM) for the analysis of fibre Bragg grating (FBG) sensors' response under anti-symmetrical strain fields. Exploiting the flexible representation of the transfer matrices in this new model, we will analytically prove that any sort of anti-symmetrical...

Analysis of the Side-Lobes of FBG Reflection Spectra from Matrix Cracks in Composites

The previously described approximated transfer matrix model (ATMM) provides insight into the strain distribution along on fibre Bragg grating (FBG) sensor. In this paper we study the influence of matrix cracks in composites on the angular frequency of the side-lobes of the FBG reflection spectra in frequency space.

Classification of composite damage from FBG load monitoring signals

This paper describes a new method for the classification and identification of two major types of defects in composites, namely delamination and matrix cracks, by classification of the spectral features of fibre Bragg grating (FBG) signals. In aeronautical applications of composites, after a damage is detected, it is very useful to know the...

Modelling non-uniform strain distributions in aerospace composites using fibre Bragg gratings

In this paper the behaviour of fibre Bragg grating (FBG) sensors under non-uniform strain distributions was analysed. Using the fundamental matrix approach, the length of the FBG sensor was discretised, with each segment undergoing different strain values. FBG sensors that are embedded inside composites, also undergo such non-uniform strain...