Larry Hill

Preparation and explosive properties of azo- and azoxy-furazans

Abstract The synthesis and properties of three energetic azo- and azoxyfurazans are described. All are derived from oxidation of 3, 4-diaminofurazan (DAF) (1) and include 3,3′-diamino-4,4′-azoxyfurazan (DAAF) (2), 3,3′-diamino-4,4′-azofurazan (DAAzF) (3) and bis[1, 2, 5] oxadiazolo [3,4-c:3′,4′-g] [1, 2, 5, 6] tetrazocine (DFT) (4). The explosive performance properties of DAAF and DAAzF have been investigated.

Flame spread through cracks of PBX 9501 (a composite octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine-based explosive)

Recent experiments involving combustion of PBX 9501 [a plastic-bonded high explosive composed of 95% octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) by weight in a plasticized, estane-based binder] under confined conditions underscore the importance of cracks and flaws in reaction violence. The presence of a small void space or alternative escape path for combustion gases at the closed end of a crack drastically alters combustion violence. In the case of a true closed-ended crack, where gases can only escape by exiting the open end of the crack, luminous combustion spreads through the closed crack at relatively low rates in the range of a few meters per second, regardless of the pressure external to the slot. Hence, external pressure determines whether reaction can progress into the restricted dimensions of the slot, but it does not necessarily determine the dynamics of the flame’s progress in the slot. When an alternative combustion-gas escape path is available at the closed end of the slot, lumin...

Application of detonation shock dynamics to the propagation of a detonation in nitromethane in a packed inert particle bed

A multidimensional implementation of DSD, formulated with the level set method, is applied to track the propagation of a detonation wave in a heterogeneous explosive consisting of an array of inert cylindrical obstacles with a liquid explosive in the interstitial space. With the Huygens assumption, the average detonation velocity through the explosive is less than that for the liquid explosive alone, due to the increased path length. When the normal detonation velocity is assumed to depend on front curvature, there is an additional, smaller reduction in the detonation velocity, which depends on the cylinder material. The detonation velocity deficits obtained in the computations are of the same order as those observed experimentally for a heterogeneous explosive consisting of a packed bed of spherical inert beads saturated with sensitized nitromethane. The DSD computations are relevant to the experimental results in the large-bead limit in which the pore dimension is large enough to support the propagation...

Cylinder Test Specification

The purpose of the cylinder testis two-fold: (1) to characterize the metal-pushing ability of an explosive relative to that of other explosives as evaluated by the E{sub 19} cylinder energy and the G{sub 19} Gurney energy and (2) to help establish the explosive product equation-of-state (historically, the Jones-Wilkins-Lee (JWL) equation). This specification details the material requirements and procedures necessary to assemble and fire a typical Los Alamos National Laboratory (LANL) cylinder test. Strict adherence to the cylinder. material properties, machining tolerances, material heat-treatment and etching processes, and high explosive machining tolerances is essential for test-to-test consistency and to maximize radial wall expansions. Assembly and setup of the cylinder test require precise attention to detail, especially when placing intricate pin wires on the cylinder wall. The cylinder test is typically fired outdoors and at ambient temperature.

On the burn topology of hot-spot-initiated reactions

We determine the reaction progress function for an ideal hot spot model problem. The considered problem has an exact analytic solution that can be derived from a reduction of A. Nichols’ statistical hot spot model [1]. We perform numerical calculations to verify the analytic solution and to illustrate the error realized in real, finite systems. We show how the baseline problem, which does not distinguish between the reactant and product densities, can be scaled to handle general cases for which the two densities differ.

Burning Crack Networks and Combustion Bootstrapping in Cookoff Explosions

Burning crack networks can play an important role in cookoff explosions of the HMX‐based explosive PBX 9501. Combustion within cracks can potentially spread to connected porosity, which is believed to develop in the heated explosive. The burning surface area would thereby increase, causing a more violent outcome. I develop an analytic model that seeks to capture the essential physical mechanisms controlling how such a scenario runs away. The calibrated model behavior is consistent with Ref. 1 tests.

Predicting Runaway Reaction in a Solid Explosive Containing a Single Crack

This work predicts the critical conditions required for the onset of reaction runaway in a narrow high‐explosive slot intended to simulate a crack. We review ongoing experiments where flames propagated through such slots at velocities up to 10 km/s, reaching pressures in excess of 1 kbar. A model is developed where slot pressurization is attributed to gas‐dynamic choking at the slot exit. The combination of choking and a pressure‐dependent reaction rate is shown to be capable of runaway reaction for a range of slot dimensions and pressures. This model agrees with experimental pressure measurements of reaction runaway in slots and provides a mechanism for the erratic burning observed with some explosives under high pressure.

THE INCIDENTAL EFFECTS OF GAPS IN DETONATING PBX 9501

The incidental effects of gaps in detonating explosives have been observed for over two centuries, yet the root cause of peripheral damage due to these features has been a partial mystery. To evaluate such damage for PBX 9501, a test series has been performed that examines single and multiply‐directed detonations crossing gaps of varying widths and angles relative to the detonation wave fronts. Damage is evaluated with steel witness plates and quantified through trench profiling and photographic analysis. In addition, streak camera traces are used to track detonations along explosive material surfaces and across gaps. Such traces allow the quantification of timing delays due to the gap reinitiation process. For some reinitiation tests, a second detonation wave is directed to interfere at varying times with the post‐gap initiation process of the first wave, thus allowing complex wave‐wave interactions to be investigated in detail. With these cumulative observations, further insight into the mechanism of ex...

PBX 9404 DETONATION COPPER CYLINDER TESTS: A COMPARISON OF NEW AND AGED MATERIAL

We present detonation copper cylinder test results on aged PBX 9404 explosive. The charges were newly pressed from 37.5 year‐old molding powder. We compare these results to equivalent data performed on the same lot when it was 3.5 years old. Comparison of the detonation energy inferred from detonation speed to that inferred from wall motion suggests that the HMX energy is unchanged, the NC energy has decreased by ∼88%, and that ∼89% of the NC decomposition products are retained in the molding powder.

A SIMPLE LINE WAVE GENERATOR USING COMMERCIAL EXPLOSIVES

We present a simple and inexpensive explosive line wave generator which has been designed using commercial sheet explosive and plane wave lens concepts. The line wave generator is constructed using PETN‐ and RDX‐based sheet explosive for the slow and fast components, respectively, and permits the creation of any desired line width. A series of experiments were performed on a 100‐mm design, measuring the detonation arrival time at the output of the generator using a streak camera. An iterative technique was used to adjust the line wave generators slow and fast components, so as to minimize the arrival time deviation. Preliminary tests achieved a wavefront simultaneity of 100 ns with a 7.0 mm/μs detonation wave. Designs, test results, and concepts for improvements are discussed.