Use of SLDV and FBG for the Detection of Delamination in Composite Laminate Beams: A Comparative Study

The use of fibre-reinforced composite laminates in aerospace, maritime and civil structure has grown over recent decades. The advantage of composites is that they have high specific strength and stiffness, as well as resistance to chemical reactivity. However, they are prone to damage, such as matrix cracking and delamination. Thus, methods for detecting internalised defects, such as delamination, are of great interest. This paper presents two separate studies for the detection of delamination damage in composite beam specimens. The first study investigates the use of a scanning laser Doppler vibrometer on fibreglass beam specimens, whereas, the second study investigates the use of embedded fibre Bragg grating sensor arrays in carbon fibre beam specimens. For both studies, a curvature-based damage index algorithm was able to evaluate the location of the delamination damage, and the slope of curvature could be used to evaluate the depth of the delamination. However, deflection measurements are significantly affected by noise and peak damage detection occurs when the delamination is located in the middle layers of the beam. Strain measurements are less affected by noise and peak damage detection occurs when the delamination is located near the surface closest to the fibre optic and at a delamination depth to beam thickness ratio of 0.583:1. Finally, practical implementation of fibre Bragg grating sensor arrays in a structural health monitoring strategy is proposed.