Process monitoring during manufacturing of large-scale composite parts

One of the inherent problems with the processing of composites is the development of internal stresses and the resulting warpage, which results in out-of-tolerance components. This investigation examines possible fiber-optic sensor methods, which can be applied to measure internal strain and thus residual stress during production. Extrinsic Fabry-Perot Interferometers (EFPI) and Bragg gratings are utilizes to monitor the strain behavior during manufacturing of large-scale composite parts. Initially, a 24 in X 18 in X 1 in thick part was manufactured using the vacuum- assisted resin transfer molding (VARTM) technique. In this part, one Bragg grating, multiple thermocouples and a resin flow sensor (SMARTweave) were integrate to measure the flow and cure behavior during production. An AGEMA thermal image camera verified the temperature history on the part surface. In addition, several EFPI's and Bragg gratings were implemented into three temperature history on the part surface. In addition, several EFPI's and Bragg gratings were implemented into three 13 ft X 32 ft X 20.3 in civilian bridge deck test specimens manufactured with the VARTM process. The Bragg gratings showed great promise to capture the changes in strain due to the residual stress during cure. The actual implementation of fiber optics into large composite parts is a challenge and the problems of sensor survivability in these parts are addressed in this study. The fiber optic measurements in combination with SMARTweave's ability to monitor flow could lead to a sensor system, which allows feedback for process control of the VARTM technique. In addition, the optical fibers will be used for health monitoring during the lifetime of the part.