O-207 Reaction Mechanisms for Rocket Motors under Mechanical Insults

July 2019
Christelle Collet, Dr Michael Sharp

Rocket motors are designed to propel payloads to their final destination by ejecting hot gases through a nozzle. The gases are produced by combustion of fuel and oxidizers, which can be separated (hybrid combustion) or mixed with each other (gun propellant, propellant grain). However, when a rocket motor and therefore, its propelling charge, is subjected to an accidental threat, it may cause a non-nominal decomposition behavior. Depending on the insult, its intensity and its duration, the reaction type may range from combustion to detonation with corresponding level of damages in the surrounding environment.

New generations of propellants may contain high energy constituents such as nitramines or energetic polymeric binders in order to attain higher or more tightly controlled burning performance. These new ingredients usually lead to a greater sensitivity to mechanical stimuli and also to smaller critical diameters. Hence, the propellant’s ability to detonate may be increased, which is a major concern for new insensitive munitions. More specifically for propellant grains, some geometrical aspects of the motor design also have to be taken into account, as they may lead to unexpected shockwave concentrations and to violent reactions.

This paper consists of an overview of possible reaction mechanisms for a rocket motor propellant under dynamic mechanical loading such as fragment or bullet impact, and how those mechanisms have evolved with the most recent advanced propelling charges. A focus is made on delayed detonations observed under such mechanical insults, with a state of the art and the main conclusions on which the international community agrees today.

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