Detonation Velocity of

The velocity of detonation (VOD) of an explosive is the rate at which the detonation wave passes through the explosive. The greater the VOD, the larger is the power of the explosive. The VOD is determined by several methods an optical, an electrical, and a comparative method. 

In the optical method, a high-speed streak camera is used to follow the flame front at about 10 million frames/s, with exposures of as httle as 0.01 ps. 

In the electrical method, a resistance element is embedded along the explosive axis, and as the detonation proceeds, the resistance changes and can be followed as a function of time on an oscDloscope. 

A comparative method uses a standard detonating fuse with known VOD. A fixed known length of the standard fuse is placed in a parallel loop with the test explosive. The two ends of the standard fuse are in contact with the test explosive and when detonated will ignite both standard and test explosive. The larger path of the standard fuse means that the start and end parts both ignite, causing the two flame fronts to meet at a point which is identified by an indentation on a lead plate adjacent to the standard fuse. The VOD of the sample can be calculated from the distances and the VOD of the standard explosive (see Exercise 14.10). 

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Velocity of detonation. 8 700m/sec (Ref 14), deton vel of 7 formulations contg MEDINA are measured and plotted in Ref 16... 

Ballistic Strength. 100% T NT (BuM ine s) Explosion Temperature. Does not expld or ignite at 360° or below Heat of Combustion. 8l8.1kcal/mole Hygroscopicity. Practically none Impact Sensitivity. Comparable to TNT Power. By Trauzl test, 103% TNT Rifle Bullet Test. No detonations from impact of. 30 cal bullet at 90 ft Thermal Stability. Unsatisfactory, loses 49% of wt in 48 hrs at 75° (International Test) Velocity of Detonation. No information Salts of (m-Nitrophenyll-dinitromethane. Milone and Massa (Ref 2) prepd several metallic salts and found that their expl power decreased with increasing atomic v/t of the metal Following are some of the expl salts K salt—yel crysts ... 

Plancastita . Expls having a greater energy, velocity of deton ana brisance compared to that of Dynamites viz,... 

Trauzl Test. 127% of PA Velocity of Detonation. 6165m/sec as detd in a glass tube 15/16 diam and 1/32 wall thickness vs 621Qm/sec for straight Nitromethane PLX corroded brass, but did not affect stainless steel, mild steel, or duriron Ref Anon, EngrDesHndbk, Explosives Series, Properties of Explosives of Military Interest , AMCP 706-177 (1971), 298... 

Sensitivity to Impact. Less sensitive thaii NG Stability. 60 minutes+ in 71° KI test Velocity of Detonation. 6885m/sec and 2000 m/sec ( ), as detd in 10mm ID glass tubes with 1 mm wall (Ref 8)... 

Compound Density Energy Streaming velocity Velocity of detonation (m s ) ... 

Liquid nitroglycerine and gelatinous explosives made from it can exhibit two stable velocities of detonation, of approximately 2000 and 8000 m s 1 respectively. The phenomenon is complicated by the occurrence of air bubbles in such explosives and has not yet been completely explained. 

TNT contains insufficient oxygen to give complete combustion of the carbon on detonation. It can, therefore, usefully be mixed with ammonium nitrate, which has an excess of oxygen. The resulting explosives, known as amatols, are more powerful and cheaper than TNT itself, but in general have a lower velocity of detonation. A proportion of 60% ammonium nitrate is perhaps the commonest of these compositions. 

Gelatine explosives, initiated by commercial detonators, will normally fire at the low velocity of detonation initially, although this may well build up quite quickly into the high velocity. For some applications a high velocity of detonation is essential. This can be ensured by the addition of barium sulphate, or other material with density exceeding 2-8, in a fine form. Such additives have the property of ensuring rapid transition to the high velocity of detonation. This is, for example, of particular importance when the explosive is to be fired under a hydrostatic head, as in submarine work. 

For routine use by unskilled personnel, the best method of measuring velocities of detonation is one due to Dautriche. The principle is illustrated in Fig. 6.5. The two ends of a length of detonating fuse are inserted in the explosive under test at a known distance apart. The mid point of the piece Mark will appear here... 

Thus by measuring the distance of the mark on the lead plate from the mid point of the fuse the velocity of detonation of the explosive under test may be calculated. In practice, it is simple to construct a rule by which the velocity can be measured directly from the lead plate. 

Mercury fulminate is a pale brownish solid, insoluble in cold water, but dissolving slightly in hot water to a solution which does not give the normal mercury reactions. In cold conditions it is stable, but at higher temperatures gradually decomposes and loses strength as an explosive. It has a density of 4-45 g ml-1 and a velocity of detonation, when compressed to a practical density of 2-5, of about 3600 m s-1. 

Lead azide is manufactured by reaction of sodium azide with either lead nitrate or lead acetate. It is a white crystalline solid, insoluble in cold water and stable on storage. It is very sensitive to friction and impact and has a velocity of detonation, when pressed to a density of 3-8, of4500 ms 1. 

Lead styphnate is a poor initiating explosive which when dry is very sensitive to friction and impact, to electrostatic discharge, and to flame. Its main use is as an additive to lead azide to improve flame sensitiveness (see p. 101). When pressed to a density of 2-6 g ml-1 it has a velocity of detonation of4900 m s l. 

The velocity of detonation of a fuse is about 6500 m s-1. This is attained in the dry process by adequate consolidation of the core during manufacture. During the wet process the necessary density is attained automatically by the method of preparing the core. Fuse usually contains about 10 g PETN per metre length. 

VOD. Velocity of detonation, usually measured in metres per second. 

High-performance explosives i.e. high density and high velocity of detonation (VOD) explosives... 

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