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 distributions, when located in the vicinity of failures such as matrix cracks or delamination of layers. This non-uniform strain distribution was created in an experimental setup. Finite element analysis was used to analytically model the strain distribution along the FBG length. The measured FBG outputs were then compared to the simulated results. There was a high amplitude correlation between the results of the measured and the simulated reflection spectra with a maximum of 0.97 among all cases.