Explosive velocity

Explosive velocity, also known as detonation velocity or velocity of detonation (VoD), is the velocity at which the shock wave front travels through a detonated explosive. The data listed for a specific substance is usually a rough prediction based upon gas behavior theory (see Chapman-Jouguet condition), as in practice it is difficult to measure. Explosive velocities are always faster than the local speed of sound in the material.

If the explosive is confined before detonation, such as in an artillery shell, the force produced is focused on a much smaller area, and the pressure is massively intensified. This results in explosive velocity that is higher than if the explosive had been detonated in open air. Unconfined velocities are often approximately 70 to 80 percent of confined velocities.

Explosive velocity is increased with smaller particle size (i.e. increased spatial density), increased charge diameter, and increased confinement (i.e. higher pressure).

Typical detonation velocities in gases range from 1800 m/s to 3000 m/s. Typical velocities in solid explosives often range beyond 4000 m/s to 10300 m/s.

VoD can be measured by using the D'Autriche method. In essence, this method relies on the time lag between the initiation of two ends of a detonating fuse, inserted radially at two points into the explosive charge at a known distance apart. When the explosive charge is detonated, it triggers one end of the fuse, then the second end. This causes two detonation fronts travelling in opposite direction along the length of the detonating fuse, which meet at a specific point away from the centre of the fuse. Knowing the distance along the detonation charge between the two ends of the fuse, the position of the collision of the detonation fronts, and the VoD of the detonating fuse, the VoD of the explosive is calculated and is expressed in km/s.

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