MECHANISM OF DETONATION IN EXPLOSIVES

Results of photographic work on the detonation of high explosives are presented and discussed in their relationship to the hydrodynamic theory of detonation. The two most important properties of an explosive are its strength and its detonation velocity. Methods for determining these quantities are described. A moving film camera of the rotating drum type is especially useful in determining detonation velocity and in studying the nature of detonation. The photographic results, which are illustrated by a number of pictures, are helpful in demonstrating various elements of the theory. These photographs illustrate the nature of detonation waves in explosives and of shock waves in air. The duration of the detonation waves in nitroglycerin and blasting gelatin is less than one millionth of a second and the duration of the shock waves produced by these explosives in air is of the same order. The high temperature of shock waves which is predicted by theory is confirmed by the intense luminosity shown in photographs. The relatively low temperature predicted for shock waves in liquids is similarly confirmed by the absence of luminous shock waves in water. Photographs are included showing the propagation of detonation from one cartridge of blasting gelatin to another across air gaps and water gaps. In the latter case no visible shock wave is produced in the water and the highly luminous after‐burning is eliminated. Calculated values of the detonation velocity for nitroglycerin, blasting gelatin and 60% gelatin dynamite are in approximate agreement with the experimentally determined values. Calculations indicate that pressures in the detonation wave may run as high as 140,000 atmospheres and temperatures to 4300°C. The shape of the detonation wave front in a high velocity explosive like blasting gelatin is apparently planar whereas in low velocity explosives it is convex. The actual mechanism of energy propagation in detonation is not clearly understood out probably involves activation of the explosive at the detonation wave front by high velocity products of the detonation which are projected forward at speeds even greater than the detonation velocity.