Predictive Capability for Hot Spot Ignition of Double Base Propellants
ARMY RESEARCH LAB ABERDEEN PROVING GROUND MD WEAPONS AND MATERIALS RESEARCH DIRECTORATE
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Propellants are almost always ignited due to thermal processes. They can be ignited by direct application of heat or by the conversion of mechanical or electrical energy to heat. However, it is not necessary to heat the bulk energetic for ignition. Local regions which achieve high temperatures, so called hot spots, are sufficient to cause rapid decomposition and reaction. For critical hot spots, the reaction in the localized region must produce heat faster than the heat transferred to the material and losses to the surrounding environment. Otherwise, the hot spot cools and can eventually stop reacting. In their monograph work on the topic, Bowden and Yoffe 1952 estimated critical hot spots at the micron 0.1 to 10um length scale, with duration of 10-5 to 10-3s and reaching 700K. The current research exercises a hydrocode to determine its ability to predict critical hot spot initiation of energetic materials resulting from thermo-mechanical coupling. For the simulations, the viscoSCRAM constitutive model was used to describe viscoelasticity, viscoplasticity, cracking and ignition in a double-base propellant when subjected to dynamic shear loading conditions. The effect of hot spot size and duration on the ignition threshold temperature was examined. The validity of the constitutive relations and the failure criterion are determined based on their ability to predict the observed mechanical response.
- Solid Rocket Propellants