Detonation Head

Both the Pb disc test and the steel dent test are of particular significance to stab detonators. As a matter of illustration, the steel dent test (Ref 10) consists of firing a detonator in direct end-on contact with a steel block. The depth of the dent produced is a measure of output. The depth, or better, the volume of the dent correlates well with initiation effectiveness. The low-rate detonation, which crushes nearly as much sand as high-order detonation, makes no dent in a steel plate. It has been demonstrated that the depth of the dent is proportionate to the excess of pressure over the yield strength of the steel of the dent block, integrated over the volume of the detonation head. It has been found that a detonator of 0.190-inch diameter or larger, which produces a dent 0.010 of an inch deep in a mild steel block, will initiate a lead of Tetryl or RDX under favorable conditions. Specification requirements for detonators to be used in fuses are usually at least 0.015 to 0.020 inch in depth, and many produce dents up to 0.060 inch deep... 

Langweiler (Ref 3) calculated the flow field behind a C-J detonation by assuming that the products maintain the velocity u2, pressure p2, and density until the passage of a rarefaction shock which reduces the velocity to zero. The rarefaction shock is assigned a velocity of (U +u2)/2. The column of forward-moving gas, which Langweiler calls a detonation head, thus has a length which increases with time and is equal to [U-(U + u2) / 2]t = (U-u t / 2. 

Its definition is given, together with definition of detonation head, at the end of the item entitled "Detonation (and Explosion) Initiation of Explosives and Shock Processes"... 

Detonation, End Effect in. Accdg to Cook (1958), pp 97-9, the end effect is "the impulse loading of a target at the end of a cylindrical charge . It has been shown by many experiments involving end effect, that a steady-state detonation head is developed in all condensed expls, whether confined or not. 

Dunkle s Syllabus (1957-1958) Shock Tube Studies in Detonation (pp 123-25) Determination of Pressure Effect (144-45) Geometrical and Mechanical Influences (145-48) Statistical Effects of Sensitivity Discussion on Impact Sensitivity Evaluation (148-49) Pressure in the Detonation Head (175) Temperature of Detonation (176) Charge Density, Porosity, and Granulation (Factors Affecting the Detonation Process) (212-16) Heats of Explosion and Detonation (243-46) Pressures of Detonation (262-63) A brief description of Trauzl Block Test, Sand Test, Plate Dent Test, Fragmentation Test, Hess Test (Lead Block Crushing Test), Kast Test (Copper Cylinder Compression Test), Quinan. Test and Hop-kinson Pressure Bar Test (264-67) Detonation Calorimeters (277-78) Measurements... 

In contrast to the shock zone, the detonation zone includes the shock zone (10 5 cm) 8t the chem reaction zone (0.1 to 1.0 cm). These two zones together make up the deton zone. In the shock zone little or no chem reaction occurs, but the pressure reaches its peak due to the shock. At or near the forward boundary of the second zone, the high temp to which the expl has been raised by compression in the shock zone initiates chem reaction. As the material moves toward the rear boundary of the chem reaction zone, the resulting expansion lowers the pressure so that this falls thruout the zone. See also Detonation Head and Its Development Addnl info on these subjects may be found in the following Refs Refs 1) G.I. Taylor, The Dynamics of the Combustion Products Behind Plane and Spherical Detonation Fronts in Explosives , PrRoySoc 200A, 235-47(1950) 2) C.G. 

Accdg to Cook, Langweiler assumed for the plain-wave deton behind the wave front a simplified constant p(x) (density-distance) and W(x) (particle velocity-distance) contour followed by a sharp (presumably discontinuous) rarefaction. He gave as the velocity of the rarefaction front the value (D+W)/2, where (D) is detonation velocity. Then he deduced that in an explosive of infinite lateral extent, the compres-sional region or detonation head of the wave should grow in thickness in accordance with the equation ... 

The geometrical model of Cook (Ref 8, pp 125-28) is based on the detonation head having flat density-distance p(x) and particle velocity-distance contours behind the... 

Fig 5.2. The Phenomenalistic Steady-State Detonation Head in an Unconfined Cylindrical Charge... 

Detonation Head and Its Development. See under Detonation (and Explosion), Initiation (Birth) and Propagation (Growth or Spread) in Explosive Substances... 

Shock Processes. Detonation Head and Detonation Edge... 

In Fig 5.1 of Cook (Ref 5, p 92) is shown development of detonation head in steady-state detonation for cylindrical unconfined and confined charges, taking into consideration the spherical shape of the wave front. 

Pugh et al. In confined charges, the steady-state detonation head, should, in this model, be somewhat larger because confinement would lower at least the initial velocity of... 

Langweiler model of detonation head. Its Engl description is given by Cook, p 91) 2) G.B. Kistiakowsky ... 

Filler, "Application of the Detonation Head Model to the Mass Loading of Explosives , UnivUtahTechRept XLV1 (1955) Contract N7-onr-45107 4) Dunkle s Syllabus (1957-... 

Shock processes and initiation) 196-98 (Progress of the detonation wave) 285-91 (The detonation head model)... 

Cook (1958), 91 3 (Steady-state detonation head for solid unconfined and confined charges) 93-7 (Experimental detonation head in gases) 97-9 (Experimental detonation head in condensed explosives) 120-22 (Detonation head model proposed in 1943) and 128 (Detonation head in ideal detonation with maximum velocity transient)... 

Accdg to Dunkle (Refs 19 20), plasmas come into play in the detonation head and are very important in EBW s (exploding bridge wires) (Ref 18) (See also Addnl Refs A, B, C, D E)... 

In an "ideal one-dimensional detonation, the expansion of the products behind the C-J plane forms a "rarefaction wave , of which the head pursues the detonation front but cannot overtake it because the wave is moving at sonic velocity in the products and they are receding from the front at just that velocity (Ref 2, pp 200-02). In an ordinary cylindrical charge (Ref 2, pp 204-06), the shape of the detonation head depends on two types of rarefactions one from the rear, corresponding to the stag-... 

Cook also gave a diagram of "development of detonation head in an ideal detonation (Fig 5.9, p 105), which includes "fronts of rarefaction waves ... 

Cook (Ref 2) determined (in collaboration with Mr O.K. Shupe), in the course of study of the shape and pressure distribution in the detonation head, that the shock velocity in steel is about 10% higher than the detonation velocity of granular RDX... 

Reynolds number, p 46), etc 61-72 (Shock relationships and formulas) 73-98 (Shock wave interactions formulas) 99-102 (The Rayleigh and Fanno lines) Ibid (1958) 159-6l(Thermal theory of initiation) 168-69 (One-dimensional steady-state process) 169-72 (The Chapman-Jouguet condition) 172-76 (The von Neumann spike) 181-84 (Equations of state and covolume) 184-87 (Polytropic law) 188, 210 212 (Curved front theory of Eyring) 191-94 (The Rayleigh transformation in deton) 210-12 (Nozzle thepry of H. Jones) 285-88 (The deton head model) ... 

Smoothly accelerating velocity-transient stabilizing at L /d = 3(+l). LD =end of vel transient and beginning of stable vel, d = diameter in cm. This type of transient, predicted by the deton head model and characteristic of non-ideal deton in point initiated chges, was observed in low density 80/20 AN/TNT, 90/l0 AN/RDX mixts, and in 50/50 cast Amatol... 

This type, predicted by the deton head model, was observed in pure RDX. It should apply to expls in chge diameters immediately above the min chge diam for ideal deton... 

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