In Situ Monitoring of Curing Reaction in Solid Composite Propellant with Fiber-Optic Sensors

Abstract

Curing activity in the preparation of solid composite propellants determines the performance of solid rocket motors in operation. Limited by the lack of effective monitoring tools, the complete curing behavior and thermal-induced curing kinetics are rarely disclosed. It is still a challenge to monitor in situ and in real-time the physical and chemical cross-linking reaction during the curing of propellant. Herein, we demonstrate a promising approach based on optical fiber capable of being implanted inside the propellant to monitor the internal stress evolution during the curing process, by taking hydroxyl-terminated polybutadiene propellant as an example. Attributed to the strain and temperature sensitivity of a pair of optical fiber gratings, the thermal-assisted physico-chemical cross-linking states of curing process have been demonstrated in detail. By tracking the stress-induced wavelength shifts of fiber gratings and calculating the curing mechanism function, the complete curing roadmap, including the viscous flow stage, gel stage, hardening stage can be clearly revealed, and the curing completion times are obtained as 154, 81, and 40 h, at the curing temperatures of 60, 70, and 80 °C, respectively. The apparent activation energy of this curing system obtained by calculation is 73.88 kJ/mol. This flexible fiber-based sensor provides an effective tool for unraveling the cure kinetic mechanism, and paves a universal pathway to guide the preparation and applications of versatile composite materials for solid rocket motors.

Strain and Temperature Sensing Based on Different Temperature Coefficients fs-FBG Arrays for Intelligent Buoyancy Materials

“…The non-uniform temperature and strain fields were measured by fs-FBG array, and the central wavelength of the fs-FBG array moved to the short wavelength direction [34]. In the final D-E stage, the high viscosity of the material increased the internal friction and hindered the progress of chemical reactions, which were mainly the physical crosslinking processes [35]. At this point, the shrinkage strain reached its maximum, approximately −4891 µε, marking the end of curing.…”