Browsing by Author "Cartwright, M."
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Item Open Access An investigation into set back force simulation in composition B fillings subjected to hot gun scenarios(2008-05-28T14:50:30Z) Cartwright, M.; Delany, P.Ammunition loaded into large calibre gun chambers, which have been heated by previous firings, can enter a hot-gun state; conservatively defined as hot if 50 rounds or more are fired in a four-hour period. In this state the temperatures of the explosive fill, such as Composition B, may easily exceed their qualification temperatures. This is potentially dangerous if the weapon misfires either by cook-off or premature shell ignition. Currently there are no standard tests that can be used to assess the behaviour of Composition B filled munitions in a simulated hot-gun condition. During firing some of the energy can be transferred to the explosive fill. Defects induced by melting and/or re-solidification of the Composition B will lead to a greater chance of accidental initiation of the explosive due to setback forces creating hotspots and ultimately resulting in an accidental in-bore explosion. The aim of this research was to investigate the conditions of this accidental initiation of Composition B in a hot gun situation at the time the projectile is likely to be cleared from the gun. It investigated whether this situation can be simulated cost effectively by examining the sensitivity of Composition B samples that were thermally conditioned in accordance with calculated temperature-time profiles. A target assembly was designed to mimic setback forces by using projectile impact. A series of tests conducted on these composition B filled targets, which had been subjected to hot gun conditions, were performed at the Cranfield Ordnance Test and Evaluation Centre (COTEC) to simulate setback effects at shot start. Mechanical energy was delivered by an impacting sabot launched from a nitrogen gas powered gun. Post firing simulation and analysis of materials were used to determine the mechanism of initiation and the severity of the event compared to the amount of force the samples were subjected to.Item Open Access A Study of the behaviour of emulsion explosives(2009-11-17T18:31:51Z) Allum, J.; Cartwright, M.This study investigated the formulation and characterisation of emulsion explosives. This included the manufacture of more than 120kg of emulsion explosive of which around 105kg was used on the explosive ordnance range in over 350 individual firings. For each emulsion composition, an average of eight firings was undertaken with which to substantiate the explosive performance data. The formulation was varied to determine the effects of water content upon the physical characteristics of the emulsion. These physical effects included thermal conductivity, particle size, viscosity and the explosive performance of the emulsion. In respect of explosive performance, microballoons were added to sensitise the emulsion and the proportions of microballoons added were altered to look at their effect on velocity of detonation, sensitivity and the brisance of the emulsions. Emulsion explosives are commonly referred, in literature, as Type 11 non-ideal explosives. This is due to their non-linear behaviour with respect to the variation of velocity of detonation with density. Traditionally, when an emulsion explosive was commercially manufactured, the water content has been kept at a minimum (12-17%). This was accepted as the way to achieve the best explosive performance, based upon the belief that an emulsion with the highest concentration of active ingredients, ammonium nitrate and oil, would give the best explosive performance. This study examined a wider range of emulsion explosive water contents than has been previously studied, from 12% to 35% water. It was found, during this study, that higher water content emulsions, specifically 25% water, had a marked increase in explosive performance. The highest velocity of detonation recorded was in a 39mm diameter tube, at 25% water content with 3% microballoons, was 5558ms-1. This was some 15% higher than any other VOD recorded in this study. The high velocity of detonation, at 25% water content, was one of a number of physical characteristics in which this water content varied from the other emulsion water contents. This study endeavored to show that emulsion explosives could exhibit two differing types of explosive reaction, thermal explosion and grain burning. This was based on the velocity of detonation and plate dent data, both of which indicated that there was a change in reaction with water content. Emulsion explosives, with a high water and high microballoon content, exhibited a thermal explosion type reaction. They exhibited Type I ideal explosive behaviour, with increasing velocity of detonation with density. Lower water content emulsion explosives, displayed the more commonly expected Type 11 non-ideal behaviour and reacted in a grain burning type detonation.