Crack Propagation and Branching in Burning Solid Propellants and Ignition of Nitramine-Based Composite Propellants

Three major tasks performed during the report period of investigation were: i) crack propagation and branching in burning solid propellants, ii) ignition of nitramine-based composite propellants under rapid pressurization, and iii) ignition of nitramine-based composite propellants by CO2 laser. Propellant samples have been recovered by interrupted burning experiments. Four modes of crack propagation and/or branching were observed. The amount of surface area generated by mixed or branched modes is substantially higher than that of the single crack propagation mode, and thus could cause sufficiently severe burning in the damaged zone to result in rocket motor failure. The crack propagation problem is analyzed through the use of basic physical principles, experimental results,and Schaper's theory of crack propagation. A set of governing dimensionless parameters which control and characterize the degree of damage has been obtained. These parameters can be used to develop guidelines for safe operating conditions of rocket motors. Ignition characteristics of a series of RDX-based composite propellants were studied. The times for the onset of light emission (t sub LE) of different propellants under rapid pressurization were compared. It is also found that propellant samples with shorter t sub LE do not necessarily show higher mass consumption, this indicates that propellant vulnerabilty should be evaluated by both t sub LE and the fraction of mass consumed.