Embedded Fiber Bragg Gratings for the Process and Structural Health Monitoring of Composite Boosters for Space Applications

Abstract

Within an ESA funded development project, fiber optical sensors were integrated into a dry wound composite booster demonstrator (L=2.5 m, D=0.8 m, t=12 mm) for the Ariane 6 launcher. The aim was to detect the resin flow front during the vacuum assisted infusion of the carbon fiber preform. Furthermore, the strains during the subsequent burst test were measured with the same sensors. Therefore 16 optical fibers with 98 inscribed fiber Bragg gratings (FBG) were manually placed into the preform within specific layers and positions. The optical fibers were successfully guided through the infusion and vacuum assembly and connected to a Micron Optics Si255 interrogator which was mounted directly at the mandrel. During the infusion and curing process the demonstrator tank and the entire measurement equipment rotated in an oven and was heated up to a temperature of 125° C during curing. Therefore a special air cooled box was designed to keep the equipment’s environmental temperature below its maximum operational temperature of 60 °C and thus guarantee its function during the whole process. The gained resin flow front data was compared with an infusion simulation carried out by the Institut für Verbundwerkstoffe GmbH, Kaiserslautern. The comparison of the results showed the potential of this measurement method for the flow front detection in thick-walled laminates. Following the manufacturing, a burst test of the demonstrator was performed. The strains were measured with the same FBGs while the demonstrator was pressurized with water until its burst pressure of approx. 450 bar.