| In a solid-rocket motor, combustion-induced crack/debond propagation could cause chamber over-pressurization and failure of a mission. To explore this malfunction of solid-rocket motors, experimental studies and theoretical simulations were conducted.; The test samples under investigation were AP/PBAN/Al and polyester-based high-elongation metalized propellants with EPDM insulators and Kevlar/epoxy cases. Crack/debond samples were installed in a windowed test chamber and rapidly pressurized in a combustion environment. The effects of chamber pressurization rate and sample's boundary condition on the development of crack/debond propagations were studied.; Three distinct modes of crack propagation (stationary, propagation, and bifurcated cracks) were observed for AP/PBAN/Al propellants, according to various chamber pressurization rates. For polyester-based high-elongation propellants, the crack propagation included propagation, zigzag, mixed, and branched modes; different types of crack-propagation modes were observed from the opposite surfaces of the recovered samples. Crack speeds related to chamber pressurization rates were obtained in a correlation form.; Debond propagation in a burning metalized propellant grain with a composite case was also studied. In general, the debond took place along the bondline with no branchings. The empirical correlations relating debond propagation speeds {dollar}Vsb{lcub}d{rcub}{dollar} to chamber pressurization rates {dollar}partial p/partial t{dollar} were obtained in a power-law form {dollar}(Vsb{lcub}d{rcub} = A({lcub}partial pover partial t{rcub})sp{lcub}n{rcub}).{dollar} It was found that the exponent n depends on debond geometries; however, the pre-exponent A is a function of material properties and sample geometries.; In the theoretical approach, the mechanisms responsible for crack initiation and bifurcation were examined. A finite-difference scheme for combustion formulation in a propagating debond cavity was coupled with a finite-element analysis for propellant structural deformation and fracture. Case expansion responsible for the debond propagation was simulated. Results for the debond model include solving combustion processes in a debond flaw; calculating pressure-driven structural deformation; and simulating combustion-induced debond propagation in a motor analog. The theoretical simulation was in good agreement with experimental observations, ensuring the applicability of this model to predict a flawed solid rocket motor. |
