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

velocity Velocity is a measurement of speed in a certain direction of motion. It is a fundamental concept in kinematics, the branch of classical mechanics that describes the motion of physical objects. Velocity is a vector (geometry), vector Physical q ...

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 Detonation () is a type of combustion involving a supersonic exothermic front accelerating through a medium that eventually drives a shock front propagating directly in front of it. Detonations propagate supersonically through shock waves with ...

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 ex ...

. Explosive velocities are always higher 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 elasticity (solid mechanics), elastic medium. More simply, the speed of sound is how fast vibrations travel. At , the speed of sound in a ...

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

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

, the

force In physics, a force is an influence that can cause an Physical object, object to change its velocity unless counterbalanced by other forces. In mechanics, force makes ideas like 'pushing' or 'pulling' mathematically precise. Because the Magnitu ...

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 and eve ...

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 to 1650m/s.

Gas explosions Gas is a state of matter that has neither a fixed volume nor a fixed shape and is a compressible fluid. A ''pure gas'' is made up of individual atoms (e.g. a noble gas like neon) or molecules of either a single type of atom ( elements such as ...

can either

deflagrate Deflagration (Lat: ''de + flagrare'', 'to burn down') is subsonic combustion in which a pre-mixed flame propagates through an explosive or a mixture of fuel and oxidizer. Deflagrations in high and low explosives or fuel–oxidizer mixtures ma ...

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 1000{{nbspm/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 The Chapman–Jouguet condition holds approximately in detonation waves in high explosives. It states that the detonation propagates at a velocity at which the reacting gases just reach sonic velocity (in the frame of the leading shock wave) as t ...

). The detonation velocity can be effectively determined by the Chapman–Jouguet (CJ) state, which represents the minimum sustainable steady detonation speed. Williams, F.A. (1985). Combustion Theory (2nd ed.). CRC Press. https://doi.org/10.1201/9780429494055

References

Explosives engineering

See also

References