Explosion waves and shock waves. VII.The velocity of detonation in cast T.N.T

The Buxton rotating-mirror camera has been used for the precise determination of velocities of detonation in cylinders of cast T.N.T. The method has an advantage over the indirect Dautriche method in that it affords a direct measure of the velocity. The effects on the velocity of detonation of the following variables have been studied in so far as each can be independently varied: ( a ) the purity and crystal size, ( b ) the diameter and ( c ) the degree of confinement. Correlation of the observations with those of the velocity of detonation shows that cast T.N.T. may undergo stable or unstable detonation according as the crystals are small or large respectively. The unstable regime is characterized by the failure of the detonation wave to be propagated uniformly over the full cross-section of the cylinder of explosive. The velocity of detonation of T.N.T. rises as the diameter of the cylinder is increased from a ‘boundary diameter’, below which there is no propagation, to a ‘limiting diameter’ at which the velocity reaches a maximum value. In castings of density 1.625 the maximum velocity is 6950 m./sec. The value of the boundary diameter is a measure of the sensitivity to propagation. The effect of heavy confinement Is to reduce the boundary and limiting diameters; the maximum velocity, however, remains unaltered and confinement has therefore the same effect as an increase in diameter in an unconfined charge.