Detonation shockwave

A detonation shock wave is an abrupt gas dynamic discontinuity across which properties such as gas pressure, density, temperature, and local flow velocities change discontinnonsly. Shockwaves are always characterized by the observation that the wave travels with a velocity that is faster than the local speed of sound in the undisturbed mixtnre ahead of the wave front. The ratio of the wave velocity to the speed of sound is called the Mach number. 

The apertures in sintered metal elements can be made so small that this arrester is able to quench detonations provided that it has sufficient mechanical strength. Particular care is required to ensure a secure anchorage of the sintered element to prevent leakage around the element caused by the impact of the shockwave (HSE 1980). 

Some designs of hydraulic (liquid seal) flame arresters have been sric-cesshilly tested for hydrogen service. NAO has designed and snccessfully tested and provided a hydraulic flame arrester for hydrogen-air applications (Straitz 1999). This design is for detonations and has dual liquid seal chambers with shockwave breakers. Rao (1980) also provides information... 

The difference between this test and the previous one is that layers of screens are added between the substance and the explosive in order to measure tiie shockwave effect of the detonator on the substance. 

Carbon disulphide burns in nitrogen monoxide and this combustion can be explosive. With dinitrogen tetroxide the mixture is supposed to be stable up to 200°C but a shockwave or a spark can cause the mixture to detonate. 

An explosive device is initiated or detonated by an explosive train — an arrangement of explosive components by which the initial force from the primary explosive is transmitted and intensified until it reaches and sets off the main explosive composition. Most explosive trains contain a primary explosive as the first component. The second component in the train will depend on the type of initiation process required for the main explosive composition. If the main explosive composition is to be detonated, the second component of the train will burn to detonation so that it imparts a shockwave to the main composition. This type of explosive train is known as a detonator. Detonators can be initiated by electrical means, friction, flash, or percussion. 

Many of the unsolved problems of physics and chemistry were concerned with combustion and detonation. A really well-developed scheme of normal combustion is seldom realized in nature. The most common form of gaseous combustion - turbulent combustion - was found to be the result of the hydrodynamic instability of the combustion process in a flow. Even in the simplest system, the physical scheme of turbulent combustion is very far from being perfectly understood. Just as in the analysis of detonative combustion, it is still possible to speak only of the universal instability of the hydrodynamic process accompanying the chemical transformation of matter. Actually, "turbulence is hardly the term for the result of the manifestation of this instability - the appearance of a multifront shockwave in the detonation front. However, the derivation of a complete physical scheme of detonation (especially in relation to condensed expls) will eventually follow from further research in this field... 

L.P. Parshev, ZhPriklMekhan i TekhnFiz 1965(5), 130-31 CA 64, 3274(1966)(Calculation of the energy of a shock wave in water) 72a) W.A. Walker H.M. Sternberg, "The Chapman-Jouguet Isentrope and the Underwater Shockwave Performance of pentolite , 4thONRSympDeton (1965), pp 27-38(26 refs) 73) R. Cheret, "Theoretical Considerations on the Propagation of Shock and Detonation Waves , Ibid, pp 78-83 74) A.B. Amster et al, "Detona-... 

Detonation An exothermic reaction that propagates a shockwave through an explosive at supersonic speed (greater than 3300ft/sec). 

Explosive substances which on initiation decompose via the passage of a shockwave rather than a thermal mechanism are called detonating explosives. The velocity of the shockwave in solid or liquid explosives is between 1500 and 9000 m s-1, an order of magnitude higher than that for the deflagration process. The rate at which the material decomposes is governed by the speed at which the material will transmit the shock-wave, not by the rate of heat transfer. Detonation can be achieved either by burning to detonation or by an initial shock. 

Explosive substances can also be detonated if they are subjected to a high velocity shockwave this method is often used for the initiation of secondary explosives. Detonation of a primary explosive will produce a... 

On suitable initiation of a homogeneous liquid explosive, such as liquid nitroglycerine, the pressure, temperature, and density will all increase to form a detonation wave front. This will take place within a time interval of the order of magnitude of 10 12 s. Exothermic chemical reactions for the decomposition of liquid nitroglycerine will take place in the shockwave front. The shockwave will have an approximate thickness of 0.2 mm. Towards the end of the shockwave front the pressure will be about 220 kbar, the temperature will be above 3000 °C and the density of liquid nitroglycerine will be 30% higher than its original value. 

By applying the fundamental physical properties of conservation of mass, energy and momentum across the shockwave, together with the equation of state for the explosive composition (which describes the way its pressure, temperature, volume and composition affect one another) it can be shown that the velocity of detonation is determined by the material constituting the explosive and the material s velocity. 

Explosives can therefore be classified by the ease with which they can be ignited and subsequently exploded. Primary explosives are readily ignited or detonated by a small mechanical or electrical stimulus. Secondary explosives are not so easily initiated they require a high velocity shockwave generally produced from the detonation of a primary explosive. Propellants are generally initiated by a flame, and they do not detonate, only deflagrate. 

Detonators are used for initiating explosives where a shockwave is required. Detonators can be initiated by electrical means, friction, flash from another igniferous element, stabbing and percussion. An example of an electrical detonator is presented in Figure 4.3. 

This chapter has so far described the total chemical energy released when a chemical explosion takes place. This energy is released in the form of kinetic energy and heat over a very short time, i.e. microseconds. In a detonating explosive a supersonic wave is established near to the initiation point and travels through the medium of the explosive, sustained by the exothermic decomposition of the explosive material behind it. On reaching the periphery of the explosive material the detonation wave passes into the surrounding medium, and exerts on it a sudden, intense pressure, equivalent to a violent mechanical blow. If the medium is a solid, i.e. rock or stone, the violent mechanical blow will cause multiple cracks to form in the rock. This effect is known as brisance which is directly related to the detonation pressure in the shockwave front. 

Knystautas J.H. Lee, Mechanisms of Initiation of Detonation in Explosive Vapor Clouds , McGill Univ, Montreal (1977), (AD-A051-854/ 8ST) 14) S.A. Gubin et al, CombustExplos-ShockWaves 14,71 (1978) 15) T. Gadian,... 

This test is used to determine detonability of a material using a blasting cap as an initiator. The blasting cap is ignited to set up a shockwave in the sample in less than 1 millisecond. If the material... 

Trade name of a new non electric device for the firing of explosive charges. The basic unit consists, of detonating cords of a plastic hose (3 mm 0), the inner wall of which is coated with a thin layer of explosive instead of electrical wires. A shock wave initiated by a special initiator passes through the tube with a speed of approx. 2000 m/s (6700 ft/s). The spectator observes this shockwave process as a flash in the hose. The plastic tube is not destroyed by the shock. 

Primary explosives are substances which unlike secondary explosives show a very rapid transition from combustion (or deflagration) to detonation and are considerably more sensitive towards heat, impact or friction than secondary explosives. Primary explosives generate either a large amount of heat or a shockwave which makes the transfer of the detonation to a less sensitive secondary explosive possible. They are therefore used as initiators for secondary booster charges (e.g. in detonators), main charges or propellants. Although primary explosives (e.g. Pb(N3)2) are considerably more sensitive than secondary explosives (e.g. RDX), their detonation velocities, detonation pressures and heat of explosions are as a rule, generally lower than those of secondary explosives (Tab. 2.1). 

As we can see in Figure 2.7, after a detonation, the shock wave naturally requires a certain amount of time t (G < t2< t3< f4), to reach a certain point. However, the maximum pressure p of the shockwave also decreases as the distance from the center of the detonation increases. 

Generally, it can be said that the damaging effect of a shockwave produced by a detonation is proportional to its impulse (impulse = mass x velocity of the gaseous explosion products) and its maximum pressure, with the impulse being the most influential factor at smaller distances and the pressure being most important at larger distances. As a rule of thumb , the distance D, which offers a chance of survival, is proportional to the cube route of the mass w of an explosive, while for typical secondary explosives at larger distances, the proportionality constant is approximately 2 ... 

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