Combustion-induced crack propagation process in a solid-propellant crack cavity

The presence of flaws in a burning solid-propellant rocket motor grain could potentially cause anomalous burning leading to unexpectedly high pressure and subsequent failure of the motor. Present understanding of the combustion and fracture processes in such flaws is limited by the difficulty of instrumenting a full-scale burning grain. Thus, the problem has been attacked by taking measurement in a lab-scale fracture/combustion test rig as well as by developing a coupled finite-element/finite-difference computer code.; In this work, emphasis was placed on the investigation of the effects of propellant type, pressurization rate, and boundary confinement on combustion-induced crack propagation in the damaged zone of a propellant grain. Both crack and debond samples were tested. Two types of propellant were studied: AP/PBAN/Al composite and polyester-based high-elongation propellants. A windowed test chamber was designed and fabricated for use in crack and debond test runs. Data acquisition systems include high-speed cameras and pressure transducers.; A theoretical model was established for simulating crack combustion process in solid propellants. The interrelated structural deformation and combustion process were simulated by integrating the following analyses: (1) transient, one-dimensional mass, momentum, and energy conservation equations for the gas phase, (2) a transient, one-dimensional heat conduction equation for the solid phase, (3) stress and strain calculations for a two-dimensional, linear viscoelastic, homogeneous, isotropic, thermorheologically simple solid propellant, and (4) fracture analysis for the propellant crack under dynamic pressure loading.; The gas- and solid-phase governing equations were solved numerically using a finite differencing technique. Stress and strain calculations were performed with a commercially available finite element code (ANSYS). Quasi-elastic approximation was used to simplify the viscoelastic constitutive equations. J-integral was calculated for the determination of fracture initiation.; A useful correlation for crack propagation speed was obtained by combining the information of experimentally observed crack speed and numerically calculated J-integral at different pressurization rates. Reasonably good agreement of crack contour and crack propagation speed between experimental and theoretical results was obtained.