DDT Validation Study

About

In the study of thermal kinetics one of the last frontiers is that of the DDT phenomenon in mixed phase materials. Since our specific research area is in Heterogenous high explosives, DDT in 2 phases is necessary. As such, we have developed a model that describes the DDT phenomenon from a semi-empiracal standpoint. This is advantageous for large simulations, where modeling the subgrid scale phenomena: hotspots, cracking, etc. is too computationally expensive.
Currently we are in the validation stage, with several proof of concept simulations having been run with the model. The model accurately represents surface burning, run distance to detonation, and cyliner expansion. Stay tuned for developments with this exciting model.

Model Description

The model is designed to be able to transition from Deflagration to Detonation. As such, it is designed as a multimaterial model using MPM method for solids and ICE materials for gaseous simulation elements. It use WSB burn model for High Explosives[1]. The in between convective burning step is proprietary and cannot yet be released online (prior to publication). The Detonation model used is designed to act as JWL++ [2]. Model calibration parameters come from [1] for burning, and [3] for detonation. The model works relatively well with either a JWL or Murnaghan EOS for reactant material, with models fits from [4] and [3] respectively. Product material is always modeled with a JWL EOS as is the norm for detonation simulations [4].
ViscoSCRAM, a simplified version of Statistical Crack Mechanics, is used as the tie between damage to the material due to impact or pressurization from nearby surface burning, and convective burning. Criteria from [5] have been adopted as the transition from surface burn to bulk burn. By far, this has been the hardest piece of the puzzle to get right. Threshold for transition from convective burning to detonation was slightly easier to choose. Five GPa is used as the threshold, as it is the point that distinguishes a weak and strong shock [6]. Thermodynamically, this value is also important, as it is the point (check this-----) at which compaction of a granular material reaches 100% TMD for the material. Furthermore, the energy input for this pressure is in the ballpark of the thermal activation energy for decomposition of the primary explosive component, HMX.

Sections

References

1. Ward, M.J., Son, S.F., Brewster, M.Q. Steady Deflagration of HMX With Simple Kinetics: A Gas Phase Chain Reaction Model. Combustion and Flame, 1998, 114, pp 556-568.
2. Souers, P.C., Anderson, S., Mercer, J., McGuire, E., Vitello, P. JWL++: A Simple reactive Flow Code Package for Detonation. Propellants, Explosives, Pyrotechnics, 2000, 25, pp 54-58.
3. Xiong, Changwei. Ph.D Thesis. University of Utahi, 2008.(Year may not be correct!)
4. Vandersall, K.S. Tarver, C.M., Garcia, F., Chidester, S.K. On the low pressure shock initiation of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine based plastic bonded explosives. J. Appl. Phys., 2010, 107.
5. Berghout, H.L., Son, S.F., Hill, L.G., Asay, B.W. Flame Spread Through Cracks of PBX 9501 (a composive octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine-based explosve)". J. Appl. Phys., 2002, 384, pp 361-277.


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