Mach Stem
Definition
The reinforced shock front that forms near a reflective surface when the direct blast wave and its reflected wave merge, producing anomalously high overpressure at ground level relative to that at height.
- Cause
- Merging of direct and reflected blast waves
- Effect
- Reinforced shock front, higher overpressure
- Location
- Near a reflective surface, e.g. ground
- Relevance
- Explosion overpressure and injury analysis
Common questions
Why does the Mach stem matter for interpreting blast damage or injuries?+
The merged shock front near ground level can produce substantially higher overpressure than at head height or further from the surface, so victims and structures at that height can show disproportionately severe blast effects compared with what the charge's stated yield alone would predict.
Is the Mach stem unique to explosives?+
No, the same reflected-shock-wave physics occurs with any strong blast wave near a reflective surface, so it appears in both explosives forensics and broader blast-injury biomechanics, not only in one explosive type.
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,...
- Chapman-Jouguet (CJ) Condition
- The steady-state condition in a detonating explosive at which the coupled shock and reaction zone travel at the same velocity (the detonation...
- 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 /...
- 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...