Dynamic measurement of internal strain on composite solid propellant constituents during laser induced combustion

Binder melt flow and ammonium perchlorate (AP) cracking have been topics for research for a long time. Both impact the burning rate dependence on pressure and the binder flow. Rapid depressurization of the combustion vessel is the most common tool used to study binder melt flow by studying the ripples on the quenched surface. Laminate propellants were used to study fundamental combustion phenomena such as the melt flow over the oxidizer/binder interface AP/hydroxyl-terminated polybutadiene (HTPB). This study starts with thermally induced strain measurements in single crystals of AP with thicknesses 1- to 2.5-mm and neat HTBP slabs then finishes with laminates of AP/HTPB. A CO2 laser ignited and burned samples over a range of heat fluxes. First ever in- situ mapping of the two-dimensional thermally-induced internal strain generated at ignition to steady state combustion were imaged using a high-speed polarization camera. Heating of the surface produced strain fields in the AP, HTPB, and laminate provide information on the thermal diffusion during the ignition and fully developed combustion. This paper demonstrates how using polarized high-speed video, the binder melt flow was more accurately observed and AP cracking mechanisms can be better studied.