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 this paper, we will show that the formation of cracks in the internal layers of composite structures alters the side-lobes of the reflection spectra of FBG sensors by adding new harmonics to them. We argue that the spread and the location of these harmonics depends on both the mechanical properties of the composite material and the location of the crack along the length of the FBG sensor. Via computer simulations and experimental measurements, we validate our hypotheses, and the results are in agreement with our model.