Detonation Velocities

Computer codes are used for the calculational procedures which provide highly detailed data, eg, the Ruby code (70). Rapid, short-form methods yielding very good first approximations, such as the Kamlet equations, are also available (71—74). Both modeling approaches show good agreement with experimental data obtained ia measures of performance. A comparison of calculated and experimental explosive detonation velocities is shown ia Table 5. 

Explosive Detonation pressure, GPa Bulk specific gravity Detonation velocity, km/s Contains high explosives Heat of detonation kj /g Excavated vol relative to equal wt of TNT... 

The calculated detonation velocity in room temperature acetylene at 810 kPa is 2053 m/s (61). Measured values are about 1000-2070 m/s, independent of initial pressure but generally increasing with increasing diameter (46,60—64). In a time estimated to be about 6 s (65), an accidental fire-initiated decomposition flame in acetylene at ca 200 kPa in an extensive piping system traveled successively through 1830 m of 76—203-mm pipe, 8850 m of 203-mm pipe, and 760 m of 152-mm pipe. 

Obtaining explosives with the proper energy, form, and detonation velocity is difficult. 

Explosives. The pressure, P, generated by the detonating explosive that propels the prime plate is direcdy proportional to its density, p, and the square of the detonation velocity, (25) ... 

The detonation velocity is contioUed by adjusting thepacking density oi the amount of added ineit matetial (26). 

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. 

The Chapman-Jongnet (CJ) theory is a one-dimensional model that treats the detonation shock wave as a discontinnity with infinite reaction rate. The conservation equations for mass, momentum, and energy across the one-dimensional wave gives a unique solution for the detonation velocity (CJ velocity) and the state of combustion products immediately behind the detonation wave. Based on the CJ theory it is possible to calculate detonation velocity, detonation pressure, etc. if the gas mixtnre composition is known. The CJ theory does not require any information about the chemical reaction rate (i.e., chemical kinetics). 

As mentioned earlier, the detonation velocity depends on the composition of the gas mixture for propane and other saturated hydrocarbons. 

Figure 7-42A. Detonation velocities for hydrogen/oxygen mixtures. Note detonation range compared to flammability range of 4% to 95%. By permission. Ref. [41]., Stuii, The Dow Chemical Co. and The American Institute of Chemical Engineers Monograph No. 10, Vol. 73 (1977).

Figure 7-53. Detonation velocity, V, static pressure, Pg, and reflected pressure, Pp developed by detonation wave propagating through hydrogen-oxygen mixtures in a cylindrical tube at atmospheric pressure at 18°C. By permission, U.S. Bureau of Mines, Bulletin 627 [43].

At times it is necessary to have a feel for overpressure as it relates to shock front velocity [49]. (See Figure 7-60). Note especially that for a reasonable detonation velocity the peak overpressure could be in the range of 700 to 1000 psi and when referenced to Figure 7-60, the extent of industrial damage would be catastrophic. The use of scaled distance is illustrated in Ref. [41]. 

Medard also examined mixts of the tetranitrate with AN and DNT. He found a mixt with 52.5% AN superior to 50/50 Amatol. Trauzl test values and deton velocities for the former were 132cc and 6520m/sec (d 1.62g/cc), with the latter yielding 112cc and 6150m/sec (d 1.60g/cc), respectively... 

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