JWL++ is a simple Reactive Flow model that includes time‐dependent reaction in prompt detonation. It consists of a Murnahan unreacted equation of state, a JWL reacted EOS, a mixer for the two EOS's and a single‐time‐constant exponential rate. The mixing can be done by four ways, using either pressure or pressure plus artificial viscosity in the rate, and also using either an analytic function or a pressure equilibrator. The model reproduces the Size Effect and detonation front curvature. Detonation failure can also be induced. JWL++ propagates also through an arbitrary geometry in 3‐D without the need for pre‐run program burn calculations. It is slower than a JWL/program “Burn” but faster than “Ignition & Growth”.
The Statistical Hot Spot shock initiation and detonation reactive flow model for solid explosives in the ALE3D hydrodynamic computer code provides physically realistic descriptions of: hot spot formation; ignition (or failure to ignite); growth of reaction (or failure to grow) into surrounding particles; coalescence of reacting hot spots; transition to detonation; and self-sustaining detonation. The model has already successfully modeled several processes in HMX-based explosives, such as shock desensitization, that can not predicted by other reactive flow models. In this paper, the Statistical Hot Spot model is applied to experimental embedded gauge data on the insensitive triaminotrintrobenzene (TATB) based explosive LX-17.
The detonation reaction rate in μs−1 is derived from Size Effect data using the relation – DUs(∂Us/∂y)−1, where y =1/Ro, where Us is the detonation velocity for a ratestick of radius Ro and D is the infinite‐radius detonation velocity. These rates are generally not constant with radius and have pressure exponents ranging from <−5 to > 5. JWL++, a simple Reactive Flow code, is run with one rate constant on many samples to compare its rates. JWL++'s pressure exponents vary from about 0.5 to 2.5, and failure occurs outside this range. There are three classes of explosives: (1) those for which the pressure exponent is between 1 and 2 and the rate is nearly constant (e.g. porous urea nitrate); (2) higher pressure explosives with a concave‐down shape and large positive pressure exponents (dense TNT); and (3) explosives with negative pressure exponents and concave‐up shapes (porous PETN). JWL++ fits only the first class well and has the most trouble with class 3. The pressure exponent in JWL++ is shown to be set by the shape of the Size Effect curve – a condition that arises in order to keep a constant reaction rate for all radii. Some explosives have too much bend to be modeled with one rate constant, e.g. Comp. B near failure. A study with creamed TNT shows that the rate constant need not be changed to account for containment. These results may well be pertinent to a larger consideration of the behavior of Reactive Flow models.
Bigplate is an advanced explosive equation of state. (EOS) test. It consists of a point detonator driving a large disc (100 mm radius) of explosive, which pushes a 0.5 mm thick copper or tantalum plate. The plate is observed by a five-beam Fabry-Perot interferometer, which has beams at 0, 10, 20,40 and 80 mm on the plate. A short Fabry gives the jump-off to high accuracy: a long Fabry runs out to IO-15 us. A detailed error analysis is given, with the final velocity measurments considered good to iO.066 mm&s. Jump-offs are measured to 0.01-0.02 ps. Spall is seen in all shots, which creates a time delay on both the first and second velocity plateaus. A 0.1 ps delay in jump-off of unknown origin is also seen at 80 mm. In brder of decreasing explosive ideality, the explosives tired have been LX-14, LX-04 and LX-17. To partially negate the time delays, the data and code runs are overlaid at each radial position between the frst and second plateaus. Traditional JWL's model LX-14 and LX-04 within accuracy, but not so for LX-17. The spa11 may be partly modeled using the pmin model but high resolution zoning is required. At longer times, spall does not appear to affect the explosive energetics. Because it includes diagonal zone crossing, Bigplate occupies a location between simple plate and cylinder tests and truly complex geometries. Hence, an EOS that fails Bigplate is not likely to move on to more complex issues. Bigplate is an excellent testbed for radically new EOS's, and the initial LX-17 mns done with Equilibrium and KINETIC CHEETAH are promising.
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