GROWTH OF BURNING TO DETONATION IN LIQUIDS AND SOLIDS,
CAVENDISH LAB UNIV OF CAMBRIDGE (ENGLAND)
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Studies were made of the growth of reaction from initiation through burning to explosion in a homogeneous thin film of nitroglycerine which is enclosed between two flat solid surfaces and initiated at its centre by an electric spark. Standard shocks were applied to single crystals of P.E.T.N., R.D.X., H.M.X., silver azide, silver, mercury and potassium fulminates and polymeric S4N4 by explosive detonators separated by thin baffles from the crystals under study. The processes leading to fragmentation, deflagration and detonation have been followed at microsecond framing rates using a Beckman and Whitley high-speed camera. The shock strengths were found either by using piezocrystals or by measuring separately shock velocities in water or lucrite. The study so far has shown the importance of habit imperfections in determining the sites at which deflagration starts. The imperfections, which may be either crystallographic notches or steps, are to some extent controllable. A problem of some interest in fracture mechanics concerns the branching of cracks. There appear to be two distinct mechanisms, the one depends on the velocity at which a crack is travelling through a solid and the other on stress wave interaction with the crack. The theoretical work was concerned with studies of the explosion process from the viewpoint of thermal explosion theory. It covers initiation by hot spots of various geometries corresponding to initiation by light, hot wires, plates and spheres and the arrival of shock wave at an impedance discontinuity.
- Combustion and Ignition