Combustion-induced crack/debond propagation in a metalized propellant

Combustion-induced crack propagation and debond in polyester-based high-elongation propellants with EPDM insulators and Kevlar/epoxy cases were investigated. Test samples were installed in a windowed test chamber and rapidly pressurized in a combustion environment. The effects of chamber pressurization rate on the development of crack propagation and debond were studied experimentally through the use of high-speed cinematography and pressure measurements. Test samples were recovered by means of the rapid chamber depressurization. Because of the high-elongation characteristic of the propellant, combinations of the crack-propagation modes were observed from the surfaces of the recovered samples. These crack-propagation and/or branching modes included unidirectional single crack, single crack with zigzag contour, crack propagation accompanied by local branchings, and crack branching with two or more cracks originating from the initial crack tip. Debond propagations in burning solid propellants were also studied. In general, debonding took place along the bond line with no branchings. An empirical correlation was obtained for debond propagation speed as a function of chamber pressurization rates.