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2 Central European Journal of Energetic Materials

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Design and operation of a small scale set back force simulator and its use in investigation into composition B fillings subjected to hot gun scenarios

Cartwright M., Delany P.

Central European Journal of Energetic Materials

2009

Vol. 6, nr 1

103-117

Ammunition fired from large calibre gun chambers may experience accelerations in the regions of 150,000 m s-2 and as a result are subjected to considerable force during the process of set back. During firing some of the energy may be transferred to the filling and any defects present in the shell filling can lead to local hotspots which may result in premature ignition of the warhead. A potential source of defects is the application of excessive heat to the ammunition either by storage in a hot environment or accidentally by leaving the ammunition in a hot gun scenario in the chamber of the gun. A hot gun scenario can be defined as arising after 50 rounds or more have been fired in a four hour period. In this scenario the filling may easily exceed the qualification temperature with two possible accidents occurring. Cook-off of the filling can result in spontaneous firing of the round or, when correctly initiated, the round may premature in the gun barrel both of which may have catastrophic results. Currently there is no standard test to evaluate the behaviour of composition B (60% RDX: 40% TNT) filled ammunition subjected to a hot gun scenario. Because of its low melting point 80 °C the liquid TNT can separate from the RDX increasing its sensitivity and increasing the probability of an in bore premature when fired. This paper describes the design and operation of a small scale simulator for set back forces and its use to investigate the conditions under which composition B fillings, subjected to a hot gun scenario, could initiate. Samples of composition B were subjected to thermal treatments to mimic hot gun conditions and then subjected to simulated set back conditions and the level of impact energy required for initiation determined. This was compared with the level for untreated samples and a possible evaluation of current hot gun procedures undertaken. The indications are that the process can be cost effective in simulating set back induced premature ignitions.

Use of a Compressed Gas Gun to Investigate Response of Explosives to a Range of Initiation Stimuli

Cartwright M., Lewis A.

Central European Journal of Energetic Materials

2007

Vol. 4, nr 4

33-43

Low velocity impacts are a source of explosive accidents. Several different mechanisms may be concurrently responsible for the initiation. Studying the effects of low velocity, comparatively long duration, impacts on energetic materials can assist in the development of explosive safety procedures and Insensitive Munitions. Careful design of the target configuration can eliminate some of the problems associated with the original Steven tests and enable the various mechanisms such as friction, shear and pinch to be isolated from other factors. In the new configuration the impact is delivered to the explosive by a spigot driven into the target by collision from a gun launched sabot. The spigot geometry i.e. flat or hemi-spherically nosed was varied as was the surface roughness and diameter of the spigot. The rate of energy delivery was varied, by varying the mass of the sabot and its velocity. The gun, 50 mm diameter, operated in the normal atmosphere conditions, NAG. Results show that pinch may be the most critical stimulus but also that friction is more significant than shear. Examination of the target debris following an event indicated that for some materials the limited confinement arising during the firing may result in a burn to detonation condition whereas for other materials the confinement was insufficient for the DDT to occur. Further work on the sample perfection and homogeneity are planned.