Impact, initiation of explosion

Up-end-Down" Method. See in Vol 3, C376-L to C376-R under Coal Mining Explosives, Testing for Permissibility in Vol 7,136-R to I37-L under Impact, Initiation of Explosion By and in Vol 8, P378-L to P379 (Table 1) under Primers ... 

Rotter Impact Test. See under Impact, Initiation of Explosion By in Vol 7,137-L ff... 

Run-Down Method. A statistical testing procedure developed at Frankford Arsenal, Philadelphia (Ref 1) which produces a more complete frequency and probability of reaction curve than the Bruceton, up-and-down, or staircase methods (see under Impact, Initiation of Explosion by in Vol 7, 136-R to I37-L). Although a larger number of tests is used than in the latter procedures, the method makes possible a better evaluation of the distribution of the population. Starting at a level expected to be between 0%... 

This subject was covered in Vol 7,135-R to I55-R, under Impact, Initiation of Explosion By , Even qualitatively, there is disagreement about the impact sensitivity of Tetryl. Most laboratories rank it between HMX and Octol, but several claim it to be as sensitive as RDX. According to Russian investigators (Vol 7,154), a quant impact sensitivity is given by Fcr, a... 

Tribochemistry is defined as decompn brought about by mechanical means, such as friction, impact, rapid shear or ultrasonic vibration See under Detonation, Spot or Hot Spot Initiation of in Vol 4, D563-R to D569-R Hot Spots in Vol 7, H170-L to H175-R and Impact, Initiation of Explosion by in Vol 7, 143-Lto I48-R (Theoretical Considerations) Addnl Ref FT. Bowden A. Yoffe, Tribo-... 

A similar explanation had already been given for the initiation of explosives by impact and friction. These phenomena have been extensively studied, particularly by Bowden and his school. Their work demonstrated two particularly important modes of initiation ... 

Detonation, Oblique Impact of a Layer of Explosive by a Metal Plate in. David et al (Ref) conducted experiments on initiation of explosives by impacts upon them of metal plates. When the metal plate came in contact with the layer of explosive, not all at once but gradually, an oblique detonation wave was initiated. In experimental arrangement shown in Fig 1, a metal plate (such as of Cu), was bent thru an angle

[Pg.461]

The following discussion on influence of hot spots in initiation of explosion by impact friction and heat is given in Dunkle s Syllabi (Refs 22 26) ... 

It is common knowledge that a blow (impact) can initiate explosion in certain substances usually referred to as explosives. Aside from superficial statements, such as the one above, the subject of impact initiation (also called impact sensitivity) of explosives has been shrouded in myth, confusion misinformation. Until recently, more time money has been invested, with less return on the investment, in studying impact sensitivity than any other aspects of explosion sensitivity. This was most aptly stated in the following quotation (Ref 4)... 

In what follows we will describe some impact machines and impact tests, ie the apparatus and methods for measuring impact sensitivity. We will then present and discuss impact sensitivity data for common explosives obtained with these machines by different laboratories. Then we will briefly consider how impact sensitivity tests have contributed to the development of the theory of initiation of explosives. Finally, we will examine impact testing from a theoretical point of view... 

We have attempted to present A B s views on impact initiation of solid explosives. 

Grit Influence on Initiation of Explosives by Impact and Friction. 

Yuill [81] investigated the sensitiveness of lead azide to impact at room temperature and at — 190°C. He found that 10-15% more energy is required for the initiation of explosion by impact at a low temperature than that at room temperature (Table 31). 

Adiabatic Compression of Entrapped Gas or Vapor as a Cause of Initiation of Explosives. It has been shown by some Brit investigators that one of the important causes of initiation of sensitive expls by mech actionfsuch as impact) is the adia-... 

The reader is urged to read Initiation of Explosives by Impact in Vol 7,135-R ff of this Encycl, Whereas that article dealt principally with the testing of expls, we shall want to include propints in the discussion. There is probably no subject in hazards analysis which is so actively studied as the role of impact, shock and thermal effects on the safety of expls and proplnts and which is as poorly understood. We have alluded to this incomplete state of theoretical development in the section of this article on Application of Computer Programming... 

Of the approximately 12 motion pictures we made of the impact initiation process, all show that the structure of the air bubble is broken down and replaced by a turbulence area. Ignition occurs at the former site of the bubble after an induction period. The compression ratio of the air bubble appears to be the major factor determining probability of initiation by impact. The mechanism for impact initiation of nitroglycerin therefore appears to be a quasi-adiabatic compression of the gas, with heat transfer accelerated by spray formation. Hot spots formed at the former site of the bubble undergo an accelerating exothermic reaction which proceeds to a deflagration. The possibility that liquid explosives under reduced pressure may be sensitized to weak impacts must be considered. 

Attention is drawn to two monographs dealing with the initiation of explosives by impact solid explosives by Afanasyev and Bobolev [49] and liquid by Dubovik and Bobolev [50]. The authors based their views on the considerable... 

---