Embedded fibre Bragg grating sensors in advanced composite materials

Fibre Bragg grating (FBG) sensors have been embedded in a number of advanced composite materials and fibre/metal laminates (FMLs). The post-fabrication FBG spectra were studied to examine the influence of manufacturing variables (such as composite stacking sequence and resin flow during processing) on the final profile of the spectrum and the functionality of the FBG sensor. Distortion and broadening of the width of the FBG spectra were observed in several of the specimens. As a result of a strong non-uniformity of the strain field caused by local asymmetric loading of the sensor, pronounced splitting of the spectra into multiple peaks was noted for FBG sensors embedded in angle-ply configurations. In contrast, the FBG spectra for the unidirectional specimens exhibited a single well-defined peak. Tensile tests carried out on these specimens showed excellent linearity within the test regime. However, for specimens exhibiting a multi-peak spectrum, it was observed that these specimens showed a tendency to produce strain anomalies during the loading event.