Cure monitoring of composites using fiber Bragg grating sensors

Residual strain and residual stress formed in cure process are two key factors that affect the quality of composite products, and both of them correlate closely with the process induced strain of pre-preg. The fiber Bragg grating (FBG) sensors were calibrated and embedded in pre-preg to in-situ monitor the strain and temperature evolution of laminates during the cure process. Based on the strain measured with the FBG sensors, the macro residual strain of the cross-ply laminate was studied. The results show that both of unidirectional and cross-ply laminates will shrink in the course of cure. There is a negative residual strain in the longitudinal direction and a positive residual strain in the transverse direction of any ply of a cross-ply laminate. The FBG sensor can be used as a tool to monitor the cure process and analyze the residual stress of composites, and makes it possible to monitor composite structures from manufacture stage to service stage continuously.