Precursor Shock in Detonation

Accdg to the paper of 1962 by Macek (Ref 14) The shift of attention to the problem of transition to detonation in solid explosives, about a decade ago, was occasioned by the awareness that the problem may be pertinent to the proper functioning of large rocket propellant grains, and was given additional impetus by the scientific approach to shock initiation. From initial qualitative suggestions of Kistiakowsky (Refs 4 6) and Ubbelohde (Ref 5) there developed the hypothesis of precursor shock, which postulates a sequence of events rather analo- 

The hypothesis was borne out by quantitative studies of the burning of explosives under confinement. Macek Gipson (Refs 7, 8 13) investigated burning of cast Pentolite and DINA, while Griffiths Groocock (Ref 10) experimented with low-density granular PETN, RDX HMX 

The region of shock formation, represented in Fig for simplicity by a single point S, can then be constructed by the method of characteristics described in the book of Courant Friedrichs (Ref 3). The pertinent velocities are given as equations 12, 

The central point of the precursor shock mechanism is that the shock wave formed at the point S is assumed to cause detonation in a manner entirely similar to initiation in shock-initiation which can be investigated by gap or impact tests, described on pp 56-60 of Ref 14 

This is so despite the fact that points of lower values of x have been exposed to high pressures for a longer time. It has been speculated in connection with gaseous systems that the effect may be due to lateral transport losses. The compression process, shown in Fig, consists of two regions up to the point S the flow is that of a simple (isentropic) compression wave, while beyond S the flow is no more a simple compression and, consequently, there is an increase of entropy across the shock front. The corresponding compression energies are expressed by equations 15 16 of Ref 14, p 51  

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