Burning Rate Measurements on Damaged Propellant Samples under Mechanical Loads
- Paper number
IAC-06-C4.P.3.04
- Author
Mr. Giuseppe Sandri Tussiwand, Politecnico di Milano, Italy
- Coauthor
Dr. Luigi T. DeLuca, Politecnico di Milano, Italy
- Coauthor
Mr. Filippo Maggi, Politecnico di Milano, Italy
- Coauthor
Prof. Giuseppe Sala, Politecnico di Milano, Italy
- Coauthor
Mr. Paolo Bettini, Politecnico di Milano, Italy
- Coauthor
Prof. Febo Severini, Politecnico di Milano, Italy
- Year
2006
- Abstract
Mechanical loads acting on a motor before its firing can produce irreversible damage on the solid propellant grain at a microscopic scale. When the motor is ignited, the state of damage of a solid propellant and the mechanical loads acting on it during deflagration can significantly alter its combustion behavior even without the presence of a macroscopic crack or excessive grain deformation. This was the topic of an experimental investigation performed at the SPLab (Laboratorio di Propulsione) on some AP/Al/HTPB and AP+AN/Al/HTPB solid propellant formulations with and without bonding agents. The burning rate of propellant samples damaged beyond the onset of dewetting and kept under tensile strain was measured and confronted to the burning rates recorded using conventional strand burners. Numerical simulations of the experiments using a simplified deflagration model on a fictitious but representative test case were also performed to investigate the thermo-physical effects responsible for this structural-ballistic interaction. So far, the following results have been obtained: - For materials containing a bonding agent, the regression rate is significantly altered if the applied strain exceeds the onset of dewetting between AP particles and the binder. - The variation of burning rate is a “fingerprint” of the superposed strain field and the original, specific microscopic structure of the material. - Since the material is not homogeneous, even a uniform strain field will produce a non- homogeneous distribution of damage. This implies that a bit of material will have a non-homogeneous distribution of burning rate. Experiments on damaged propellant slabs under strain showed an enhanced generation of vorticity on a microscopic level, particularly at spots where the damage distribution was not homogeneous. This means that the combustion noise is greatly enhanced in highly damaged regions. - If the material does not contain a bonding agent (e.g. formulations based on nitramines and binder, or particular propellants where no bonding agent between solid particles and binder exist), a progressive increase of the burning rate with the applied strain is to be expected. - The increased mass burning rate might be caused by an increased burning surface on a microscopic level: debonded AP particles ignite below the “reference” burning surface through conduction in the gas phase between the debonded particles and the binder matrix.
- Abstract document
- Manuscript document
IAC-06-C4.P.3.04.pdf (🔒 authorized access only).
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