Fiber-Optic Raman Analysis for Composites and Solid Rocket Motors

We propose developing a compact, optical fiber-based Raman scattering instrument for rapid, in-situ analysis of composites, solid rocket motors, and propellants. The instrument will incorporate diode laser-based, full-spectrum Raman scattering forcontinuous in-situ remote monitoring of the composite and propellant chemistry. Narrow well defined Raman peaks and lack of sample preparation requirement make Raman scattering well suited for in-situ analysis of composites and solid rocket propellants.Raman spectroscopic analysis can be made via small (200 mm core), inert, silica/silica clad optical fibers. One fiber is used for sample excitation via laser diode, and another fiber collects the Raman scattered light and carries the signal to a remote,portable spectrograph. A semiconductor laser diode offers long life, can be very compact, and can operate at near-IR wavelengths where sample fluorescence is minimized while taking advantage of the very sensitive and full-spectrum capabilities of siliconCCD array Raman spectrum detection. Many optical fibers could be multiplexed to allow depth profiling of selected polymer/fiber composites and/or solid propellant regions such as bond line and areas adjacent to casing liner. Optical fibers could be castdirectly into a composite structure while the resin and fabric are being laid up. This would allow polymer chemistry monitoring during the curing process to ensure proper curing conditions and reduce excess cure time. Similar optical fibers could becast into witness panels of propellant mixtures without damaging the surrounding propellant, liners, insulator, or case structure. The Raman spectra will be used to monitor curing, migration of plasticisers and other contaminants, and other aging effectsthat could alter propellant chemistry. Phase I will determine the feasibility of casting optical fibers into typical resin/fiber composite systems and inert, propellant substitutes to measure propellant chemistry using Raman spectroscopy. Laboratoryresults have demonstrated the ability of Raman scattering to quickly identify the basic components used in polymer composites, solid rocket propellant, and commercial and military explosives.Rapid, in-situ determination of solid rocket propellantchemistry could greatly reduce the need for destructive testing to determine the chemical state of new and aging rocket motors. Similar technology can be applied to many composite manufacturing systems such as aircraft and vehicle manufacturing where epoxycuring and chemical stability issues are very important for service life.