Shock waves, explosion

Crane Sh. L., University of California Press, Berkeley, California 1982 Los Alamos Shock Wave Profil Data. Hrsg. Morris, Ch. ., University of California Press, Berkeley, Los Angeles, London 1982 Shock Waves, Explosions and Detonations, Hrsg. Bowen, J. Ft., Manson, N., Oppenheim, A. K. und Soloukhin, R. /., AIAA, New York 1983 (Progress in Astronautics and Aeronautics, Vol. 87)... 

Explosives are materials that combust at an extremely fast rate to form a pressure-shock wave. Explosives can be classified into two groups low explosives, with pressure waves traveling at less than 3,300 feet per second (fps), and high explosives, with transonic shock waves (>3,300 fps). 

A means provided for the release of high pressures caused by explosion. Dust and vapor explosions create a shock wave. Explosion venting systems are commonly installed where there may a risk of a dust explosion. They typically incorporate a predetermined blow out panel, which, if an explosion occurs, allows the shock wave... 

Air Blast Unconfined Gaseous Detonations," Dynamics of Shock Waves, Explosions and Detonations, Vol. 94, edited by R.Bowen et al. Progress in Astronautics and Aeronautics, AIAA, Washington, DC, 1985, pp. 556-566. 

W.B. Benedick, J.H. Lee, R. Knystautas, Large scale experiments on the transmission of fuel-air detonations from two-dimensional channels Progress. Astronautics and Aeronautics, in Dynamics of Shock Waves, Explosions and Detonations, ed. by J.R. Bowen, N. Manson, A.K. Oppenheim, R.I. Soloukhin, vol. 94 (AIAA, New York, 1984), pp. 546-555... 

A laser beam is capable of putting so much energy into a substance in a very short space of time that the substance rapidly expands and volatilizes. The resulting explosive shock wave travels through the sample, subjecting it to high temperatures and pressures for short times. This process is also known as ablation. 

A great deal of experimental work has also been done to identify and quantify the ha2ards of explosive operations (30—40). The vulnerabiUty of stmctures and people to shock waves and fragment impact has been well estabUshed. This effort has also led to the design of protective stmctures superior to the conventional barricades which permit considerable reduction ia allowable safety distances. In addition, a variety of techniques have been developed to mitigate catastrophic detonations of explosives exposed to fire. 

Explosives are commonly categorized as primary, secondary, or high explosives. Primary or initiator explosives are the most sensitive to heat, friction, impact, shock, and electrostatic energy. These have been studied in considerable detail because of the almost unique capabiUty, even when present in small quantities, to rapidly transform a low energy stimulus into a high intensity shock wave. 

Other. Because a foam consists of many small, trapped gas bubbles, it can be very effective as a thermal insulator. Usually soHd foams are used for insulation purposes, but there are some instances where Hquid foams also find uses for insulation (see Eoamed plastics Insulation, thermal). Eor example, it is possible to apply and remove the insulation simply by forming or coUapsing the foam, providing additional control of the insulation process. Another novel use that is being explored is the potential of absorbing much of the pressure produced by an explosion. The energy in the shock wave is first partially absorbed by breaking the bubbles into very small droplets, and then further absorbed as the droplets are evaporated (53). 

In commercial practice, powdered explosives on an ammonium nitrate basis are used in most cases. Typical detonation velocities are between 1800 and 3500 m/s depending on the metal system to be bonded. The lower detonation velocity range is preferred for many metal systems in order to minimize the quantity of solidified melt associated with the bond-zone waves (12). In addition, subsonic detonation velocity explosives are required for the parallel cladding technique in order to avoid attached shock waves in the coUision region, which preclude formation of a good bond. 

Explosions are either deflagrations or detonations. The difference depends on the speed of the shock wave emanating from the explosion. If the pressure wave moves at a speed less than or equal to the speed of sound in the unreacted medium, it is a deflagration if it moves faster than the speed of sound, the explosion is a detonation. 

The propagation of a shock wave from a detonating explosive or the shock wave induced upon impact of a flyer plate accelerated, via explosives or with a gun, result in nearly steady waves in materials. For steady waves a shock velocity U with respect to the laboratory frame can be defined. Conservation of mass, momentum, and energy across a shock front can then be expressed as... 

We assume that in (4.38) and (4.39), all velocities are measured with respect to the same coordinate system (at rest in the laboratory) and the particle velocity is normal to the shock front. When a plane shock wave propagates from one material into another the pressure (stress) and particle velocity across the interface are continuous. Therefore, the pressure-particle velocity plane representation proves a convenient framework from which to describe the plane Impact of a gun- or explosive-accelerated flyer plate with a sample target. Also of importance (and discussed below) is the interaction of plane shock waves with a free surface or higher- or lower-impedance media. 

An important application of the impedance match method is demonstrated by the pressure-particle velocity curves of Fig. 4.9 for various explosives. Using the above method, the pressure in shock waves in various explosives is inferred from the intersection of the explosive Hugoniot with the explosive product release isentropes and reflected shock-compression Hugoniots (Zel dovich and Kompaneets, 1960). The amplitudes of explosively induced shock waves which can be propagated into nonreacting materials are calculable using results such as those of Fig. 4.9. 

Ahrens, T.J., and O Keefe, J.D. (1977), Equation of State and Impact-Induced Shock-Wave Attenuation on the Moon, in Impact and Explosion Cratering (edited by Roddy D.J. et al.), Pergamon Press, New York, pp. 639-656. 

R.N. Orava and R.H. Wittman, Techniques for the Control and Application of Explosive Shock Waves, in Proc. 5th Int. Conf. on High Energy Fabrication, University of Denver, Denver, 1975, p. 1. 

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