Monitoring of process induced strains in a single fibre composite using FBG sensor: A methodological study

A partially embedded long fibre-Bragg grating (FBG) into an epoxy cylindrical specimen is used to monitor the strain distribution evolution along its axis when subjected to subsequent cycles of thermal ageing at 70° and 110 °C. Assuming a total volume reduction of 2.5% at full cure, the epoxy conversion at the end of the thermal cycles was found ∼85%. Using strain data from the FBG, the coefficient of thermal expansion was evaluated as ∼11.5 × 10−5 C−1. Based on the strain data from the FBG, numerical simulations of an equivalent thermo-elastic matrix were performed to obtain the residual stresses in the specimen at the end of the thermal cycles. The results demonstrate the capability of FBG sensors in providing important information on the degree of cure and evolution of fabrication induced strains inside the epoxy.