Metal plate free-surface velocity

The determination of the [Pg.120]

The metal plate free-surface velocity may be determined ty different c cal methods or by the electrocontact type probes and oscilloscope technique. 

Figure 4.35. The determination of the metal plate free-surface velocity by electrocontact probes...

As already stated, the metal plate free-surface velocity can be experimentally determined by electrocontact type or velocity probes/oscilloscope technique, and by optical methods. 

The shock wave velocity in the metal plate and the metal plate free-surface velocity (v j,) can be calculated as follows. 

The metal plate free-surface velocity (v p) is calculated on the basis of the time interval between the second and third pairs of probes. This time interval includes the time of the motion of the plate free surface (ts) and the time of the shock wave motion through the second screen ( 2). The height of the ring (/ ) is so taken that the time of the motion of the plate free surface is less than the time of the shock wave motion (/ ) through the plate ... 

With respect to the experimentally obtained dependence between the metal plate free-surface velocity and the plate thickness, which is related to the characteristics of the tested explosive and the applied plate thickness, two cases are possible, as shown in Figure 4.38 ... 

The other group of methods includes those that are based on the registration of the state originated after the shock wave reflection from a barrier. For instance, the detonation pressure m be determined on the basis of the measurement of a thin metal plate firee-surface velocity. The plate free-surface velocity can be determined using optical methods or the electrocontact type of probes and oscilloscope technique. The methods based on the determination of the shock wave velocity through an inert material, e.g., the Aquarium test, are also included in this group. The time resolution of these methods may be on a nanoseconds scale, and even less than a nanosecond, e.g., w en laser interferometry technique is used. Since the processes in the shock fi-ont occur on a nanosecond scale, the present-day techniques are still inadequate to study the detonation wave shock front. 

When the metal plate driven by the explosive begins to move, the argon gaps near the plate surface get closed, vdiich yields a brilliant flash of light of short duration, recorded on the film. After the free surface passes the known distance (cf), it closes the central gap and yields another flash of light. The time interval between these two flashes corresponds to the time of the plate free-surface motion, and it is used for the calculation of the plate free-surface velocity. 

The aquarium test is essentially a modification of the flying plate test in which the metal plate is replaced by a layer of water or some other optically transparent material, such as Plexiglas. Instead of the determination of the plate free-surface velocity, the traveling of the shock wave through an inert and optically transparent material is viewed as a function of time. When having the shock wave velocity vs. distance dependence, and knowing the adiabatic shock equation of the inert material used, the mass velocity behind the shock wave front and the detonation pressure of a tested explosive may be calculated. 

Fauquignon et al stated in "Introduction (Ref 12, p39), that most of the experimental methods concern velocity measurements in an inert medium close to the explosive, eg a) Free-surface velocity imparted to metallic plates of increasing thicknesses (Refs 2, 5, 6, 10,... 

Unfortunately, such a more general comparison of calculated detonation pressures with measured detonation pressures is complicated by the fact that experimental determinations of this property are inherently difficult and thus often inexact. The C-J detonation pressure cannot be measured directly at the current state of the art, but rather, it is deduced from experimental determinations of shock velocities and free-surface velocities of metal plates adjacent to the explosive.17... 

A third method for measuring velocities employs Lucite and argon gaps in a similar way but does not use the wedge. Instead, the free-surface velocity is measured across a fixed gap between a Lucite block and the metal surface. Shock velocities are measured by attaching small metal blocks of various thicknesses to the surface of the main plate and recording the transit time of the shock wave in each by the argon-gap method. ... 

Craig, from his free-surface velocity measurements with very thin metal plates, estimates that the reaction zone thickness of liquid TNT is about 1 x 10 cm and that of nitromethane is less than 2 x 10 cm7 ... 

The solid flow only covers zone D and some mesh elements there are blocked to the solid flow to fit the thickness of iron ore fines layer which are illustrated in Figure 1. Conservation equations of the steady, incompressible solid flow could be defined using the general equation is Eq. (6). In Eq. (6), physical solid velocity is applied. Species of the solid phase include metal iron (Fe), iron oxide (Fc203) and gangue. Terms to represent, T and 5 for the solid flow are listed in Table n. Specific heat capacity, thermal conductivity and viscosity of the solid phase are constant. They are 680 J/(kg K), 0.8 W m/K and 1.0 Pa s respectively. Boundary conditions for solid flow are Sides of the flowing down channels and the perforated plates are considered as non-slip wall conditions for the solid flow and are adiabatic to the solid phase up-surfeces of the solid layers on the perforated plates are considered to be free surfaces at the solid inlet, temperature, volume flow rate and composition of the ore fines are set depending on the simulation case At the solid outlet, a fiilly developed solid flow is assumed. 

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