Explosive velocity, also known as detonation velocity or velocity of detonation (VoD), is the

velocity Velocity is the directional speed of an object in motion as an indication of its rate of change in position as observed from a particular frame of reference and as measured by a particular standard of time (e.g. northbound). Velocity i ...

at which the

shock wave In physics, a shock wave (also spelled shockwave), or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a me ...

front travels through a detonated

explosive An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An expl ...

. Explosive velocities are always faster than the local

speed of sound The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elastic medium. At , the speed of sound in air is about , or one kilometre in or one mile in . It depends strongly on temperature as we ...

in the material. If the explosive is confined before detonation, such as in an

artillery shell A shell, in a military context, is a projectile whose payload contains an explosive, incendiary, or other chemical filling. Originally it was called a bombshell, but "shell" has come to be unambiguous in a military context. Modern usage so ...

, the

force In physics, a force is an influence that can change the motion of an object. A force can cause an object with mass to change its velocity (e.g. moving from a state of rest), i.e., to accelerate. Force can also be described intuitively as a ...

produced is focused on a much smaller area, and the

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country a ...

is significantly intensified. This results in an 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 for organic dust mixtures range from 1400–1650m/s.

Gas explosions A gas explosion is an explosion resulting from mixing a gas, typically from a gas leak, with air in the presence of an ignition source. In household accidents, the principal explosive gases are those used for heating or cooking purposes such as na ...

can either

deflagrate Deflagration (Lat: ''de + flagrare'', "to burn down") is subsonic combustion in which a pre-mixed flame propagates through a mixture of fuel and oxidizer. Deflagrations can only occur in pre-mixed fuels. Most fires found in daily life are diff ...

or detonate based on confinement; detonation velocities are generally around 1700 m/s but can be as high as 3000m/s. Solid explosives often have detonation velocities ranging beyond 4000 m/s to 10300 m/s. Detonation velocity can be measured by the Dautriche method. In essence, this method relies on the time lag between the initiation of two ends of a detonating fuse of a known detonation velocity, 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 detonation velocity of the detonating fuse, the detonation velocity of the explosive is calculated and is expressed in km/s. In other words "VOD is the velocity or rate of propagation of chemical decomposition/reaction." And for high explosives, it is generally above 1000m/s. In the cases where a material has not received dedicated testing, rough predictions based upon gas behavior theory are sometimes used (see Chapman-Jouguet condition).

References

Explosives engineering {{explosive-stub

See also

References