Chapman-Jouguet (CJ) Condition
Definition
The steady-state condition in a detonating explosive at which the coupled shock and reaction zone travel at the same velocity (the detonation velocity, VoD); the CJ pressure and velocity are characteristic of each explosive formulation.
- Describes
- Steady-state detonation condition
- Key equality
- Shock and reaction zone travel at same velocity
- Named property
- Detonation velocity (VoD)
- Varies by
- Explosive formulation
Common questions
Why is the CJ condition treated as a steady state?+
Once the shock front and the chemical reaction zone lock together at a common velocity, the detonation propagates without further acceleration or deceleration, giving each explosive a characteristic, reproducible detonation velocity.
How is this used forensically after a blast?+
Because VoD and CJ pressure are characteristic of a formulation, investigators can compare observed blast damage and fragmentation patterns against known CJ parameters to narrow down which explosive type was likely used.
Related terms
- Brisance
- The shattering power of a detonating explosive, distinct from heave (bulk displacement). Measured by the Trauzl lead block test. High-brisance explosives (RDX,...
- Deflagration-to-Detonation Transition (DDT)
- The acceleration of a deflagrating burn front to supersonic detonation velocity, triggered by confinement. Relevant to understanding how improvised devices using low...
- DMDNB Taggant
- Dimethyldinitrobutane, a detection marker incorporated into plastic explosives (including Semtex) under the ICAO 1991 Convention on the Marking of Plastic Explosives; allows...
- Dynamic Pressure
- The pressure component due to mass flow of gas behind the shock front, proportional to gas velocity squared; the blast wind that...
- Friedlander Waveform
- The idealised time-pressure history at a point in air following a blast: instantaneous rise to peak overpressure at shock arrival, exponential decay...
- Hopkinson-Cranz Scaling
- The law relating peak overpressure and positive-phase duration to the ratio of range to cube-root-of-charge-mass (the scaled distance Z = R /...
- Mach Stem
- The reinforced shock front that forms near a reflective surface when the direct blast wave and its reflected wave merge, producing anomalously...
- Mott Formula
- An empirical relationship, derived from wartime UK research by N.F. Mott, predicting the statistical distribution of fragment masses from a metal casing...
- Peak Static Overpressure (Ps)
- The maximum pressure increase above ambient at the shock front, the primary structural damage parameter, scaling with the inverse cube root of...