Determination of process-induced residual stress in composite materials using embedded fiber optic sensors

A method to determine process-induced residual stress in composite materials using strain measurements from embedded fiber optic sensors is presented. This method allows non-destructive, real-time determination of residual macrostress in composite materials and may be useful for both process monitoring and control. Extrinsic Fabry-Perot interferometer strain sensors were embedded in Hercules AS4/3501-6 graphite/epoxy composite specimens prior to cure. The specimens were cured in a press, and the internal strains and temperatures developed during processing were monitored and recorded. Residual macrostresses were computed using these measurements and a viscoelastic model of the material. The results compare favorably with previous analytical predictions and experimental measurements from a destructive technique.