Initiation phenomena in solid explosives produced by strong shock waves are described. Shock pressures in the explosive are between 20 and 200 kbar. It is demonstrated that in the usual case the shock wave travels not as an inert shock, but as a shock to which the explosive contributes energy, probably from reaction at voids and defects. This slightly reacting shock travels at increasing velocity for some distance, typically 1 cm in the experiments described, and then in a travel of perhaps 0.01 cm becomes full detonation, moving at full velocity. The increase to full detonation velocity occurs without overshoot. Experiments demonstrating the variation of sensitivity to shock with density, grain size, and other properties are discussed. The explosives studied are cyclotol B, TNT, plastic-bonded HMX, and nitromethane-carborundum mixtures.

Experimental studies of the initiation of liquid explosives by strong plane shocks (pressures 50 to 100 kbar) are described. These experiments demonstrate thermal explosion as a result of shock heating in the explosive. When the shock enters the explosive, the explosive is heated. After a delay, detonation in the heated, compressed explosive begins at the interface, where the explosive has been hot longest. The detonation proceeds through the compressed explosive at a velocity greater than the steady state velocity in uncompressed explosive, overtaking the initial shock and overdriving detonation in the unshocked explosive. Most of the work has been done on nitromethane, but molten TNT, molten DINA, Dithekite 13, and single crystals of PETN are shown to behave in the same way. Experiments showing the effects of bubbles and shock interactions in the explosive are presented.

The detonation velocity of PBX‐9502, an explosive consisting of 95 wt% TATB and 5 wt% Kel‐F 800, was measured precisely over a range of charge diameters at 75°C, 24°C, and −55 °C. The diameter‐effect curves obtained by plotting detonation velocity versus the reciprocal of charge radius were found to differ from those reported in the literature for other solid and liquid explosives, being concave upward at large diameters. The curve at 75°C was found to be a straight line at small diameters and thus simulates the behavior of a homogeneous explosive. At intermediate charge diameters, the effect of varying the temperature by 130°C was quite small. The failure diameter varied from 5.85 ± 0.15 mm at 75°C to 10.5 mm at −55 °C.

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In a recent issue of this journal [M. A. Cook and W. S. McEwan, J. Appl. Phys. 29, 1612 (1958)] and in a recent book [Melvin A. Cook, The Science of High Explosives (Rheinhold Publishing Corporation, New York, 1958), 1st ed., pp. 158, 420–426], a sequence of framing camera pictures was presented, and the sequence was interpreted as evidence that, as the result of the detonation of a quantity of explosive, a plasma was ejected into the atmosphere, and that the plasma exhibited a strong cohesive force. This paper presents pictures of an essentially identical subject, taken at three exposure times: the same exposure time used for the sequence in the references (4 μsec); 1/20th of that time; and 1/400th of that time. These pictures show that the phenomena are those of a shock wave, and that no new assumption of cohesive force is necessary to interpret the pictures. A simple analysis of the shock wave interpretation using the usual theory is presented to show that the interpretation is consistent with the known properties of air and the explosive used.