Shock amplitude

McQueen et al. (1982) demonstrated that by placing a series of high-impedance transparent fluids (called optical analyzers) over the sample at a series of thicknesses less than d in the target that the overtaking rarefaction (sound) velocity can be accurately obtained. Arrival of rarefaction waves rapidly reduce the shock pressure. These wave arrivals could be very readily detected by the change in light radiance caused by the onset of a decrease in shock amplitude when the rarefaction wave caught up to the shock front. The... 

An important aspect of micromechanical evolution under conditions of shock-wave compression is the influence of shock-wave amplitude and pulse duration on residual strength. These effects are usually determined by shock-recovery experiments, a subject treated elsewhere in this book. Nevertheless, there are aspects of this subject that fit naturally into concepts associated with micromechanical constitutive behavior as discussed in this chapter. A brief discussion of shock-amplitude and pulse-duration hardening is presented here. 

It is no surprise that increased shock amplitude should result in increased residual strength or material hardness. Increasing shock amplitude results in... 

The time rates of change of the shock amplitude can also be obtained for other variables by differentiating the jump conditions, (A.6) and (A.7), along a shock path to obtain... 

As the wave evolves from that point, the losses connected with rearward expansion decrease. If a charge of a small diam is considered, then lateral expansion depends on the path over which the wave has traveled. The increase in cross section of a cylinder, i.e., expansion in the lateral direction, leads to a reduction in pressure and to a decrease in the deton velocity in comparison with detonation propagating in a constant cross-section cylinder. The decrease in deton vel causes, in turn, the diminution of shock amplitude wave and impairs the conditions under which the reaction can proceed. The loss caused by lateral expansion is known as lateral loss. Propagation of detonation is possible only if this loss is not smaller than a certain limit, which is characteristic for each expl... 

Fig 13 Critical acceleration and energy release rate curves determined from long-duration pulse experiments, as functions of shock amplitude v in PBX 9404. Energy rate shown is the net result of mechanical dissipation and exothermic chemical reaction. Following thermochemical convention, energy release rate due to exothermic reaction is denoted as a negative value of H ... 

Longueville et al (Ref 100) used flyer plates to study the shock sensitivity of RDX (and other expls) as a function of shock amplitude and shock duration. Their results for RDX are shown in Fig 6... 

Clearly packing density exerts a pronounced influence on shock sensitivity if shock sensitivity is gaged by input shock amplitude... 

The writer s results for RDX at 1.54g/cc, obtained in the test system shown in Fig 5, were as follows (threshold values are shock amplitudes in the RDX at the inert barrier/RDX interface) ... 

These generalizations are illustrated in Fig 20 (from Ref 40), which also shows that 02 and mixts of 02 and N2 sensitize PETN, while all other gases tested desensitize it to shock. Note that shock amplitude in Fig 20 is given in terms of barrier thickness, ie, the thicker the barrier the more shock-sensitive the PETN-gas combination... 

The attenuation of the reflected shock wave over 12 cycles of reflection within cylindrical and spherical vessels has been examined. Computations without added dissipation simulate the qualitative features of the measured pressure histories, but the shock amplitudes and decay rates are incorrect. Computations using turbulent channel flow dissipation models have been compared with measurements in a cylindrical vessel. These comparisons indicate that the nonideal aspects of the experiments result in a much more rapid decay of the shock wave than predicted by the simple channel flow model. Dissipation mechanisms not directly accounted for in the present model include multidimensional flow associated with transverse shock waves (originating in detonation or shock instability) separated flow due to shock wave-boundary layer interactions the influence of flow in the initiator tube arrangement and real gas (dissociation and ionization) effects and fluid dynamic instabilities near the shock focus in cylindrical and spherical geometries. 

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