Shock pressure

Compounds pressure, gas, and heat when subjected to shock, pressure, high temperature or other energy sources excludes inert gases. 

For shock waves in solids, the shock pressure P is typically much greater than the initial pressure Pq, which is normally ambient atmospheric conditions, so that Pq is usually neglected. Eq can also be taken to be zero, sinee internal energy is a thermodynamie state funetion and ean be refereneed to any initial state. Removing Eq and Pq from the jump conditions results in their eommon form... 

The shock pressures attainable with direct explosive contact depend on the shock impedance (shock velocity times material density) of the specimen material, and on the explosive energy of the contacting explosive. High-energy explosives placed directly on high-shock impedance materials can produce shock pressures of several tens of GPa. 

One drawback of systems shown in Fig. 3.1 is that the initial peak shock pressure on the specimen is limited and not well sustained. It immediately starts to decrease, which leads to an attenuation of the shock front as it propagates through the specimen. Attenuation of the shock is detrimental to the accuracy of the resulting experimental data. Also, the late-time release of pressure at the specimen surface is nonplanar, which rules out obtaining accurate information on the specimen s unloading behavior. 

These guns were developed to attain much higher impact velocities than those available with powder guns (Crozier and Hume, 1957 Curtis, 1962). Peak velocities in the 7-8 km/s range can be routinely attained, with peak shock pressures approaching 1 TPa in high impedance materials. 

Shock Luminescence. Some transparent materials give off copious amounts of light when shocked to a high pressure, and thus they can serve as shock arrival-time indicators. A technique used by McQueen and Fritz (1982) to measure arrival times of release waves is based on the reduction of shock-induced luminescence as the shock pressure is relieved. Bromoform, fused quartz, and a high-density glass have been used for their shock luminescence properties. 

Three pressure units are commonly in use in shock-wave research kilobar (kbar), gigapascal (GPa), and megabar (Mbar). These are equal to 10 , 10 , and 10 dyne/cm, respectively. The shock pressure range of primary interest in this review article is 100- 4000 kbar. 

Figure 4.4, Shock pressure versus specific volume for several standard materials.

Thus, from the form of (4.7), shock pressure is given as the sum of a linear and quadratic term in particle velocity, based on the data of Table 4.1. A pressure volume relation can be obtained by combining (4.6) with (4.1) to yield... 

Figure 4.5. Shock pressure versus particle velocity for various standard materials.

If the Hugoniot of the flyer plate (.4) and the target (B) are known and expressed in the form of (4.7), the particle velocity Ui and pressure Pi of the shock state produced upon impact of a flyer plate at velocity, Ufp, may be calculated from the solution of the equation equating the shock pressures in the flyer and driver plate ... 

Figure 4.9. Shock pressure versus particle velocity for engineering materials, geological material, and explosive detonation products. Intersection of detonation product curves with nonreactive media predicts shock pressure and particle velocity at an explosive sample interface. (After Jones (1972).)...

Figure 4.15. Shock pressure versus specific volume for calcia and fused quartz indicating three regimes fused quartz, low-pressure regime is fused quartz, mixed phase regime, and high-pressure regime representing stishovite. In the case of calcia, the low-pressure phase is the B1 structure, mixed phase is indicated, and the high-pressure phase regime is in the B2 structure.

Figure 4.19. Shock pressure versus density Hugoniot states for initially porous quartz. Density of starting material is indicated on various curves. Porous properties of stishovite are represented by curves with 1.75, 2.13, and 2.65 Mg/m, initial density, whereas coesitelike properties are represented by 0.2-0.8 Mg/m curves (after Simakov and Trunin (1990)).

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... 

Figure 6.3. Stress-strain response of shock-loaded 6061-T6 A1 as a function of peak shock pressure showing minimal shock strengthening.

Increasing the driver plate velocity and driver plate thickness for a fixed sample assembly results in an increased peak shock pressure and pulse duration. As far back as the review of Appleton [32] in 1965 on metallurgical... 

Doran, D.G., Measurement of Shock Pressures in Solids, in High-Pressure Measurement (edited by Giardini, A.A. and Lloyd, E.C.), Butterworths, Washington, DC, 1963, pp. 59-86. 

Batsanov, S.S., Structural Aspect of Shock-Wave Propagatio in Crystals, in Proceedings, First All Union Symposium on Shock Pressures, Vol. 2 (edited by Batsanov, S.S.), Moscow, 1974, pp. 1-10. Translation, Sandia National Laboratories Report No. SAND80-6009, April 1980. 

Grady, D.E., Phase Transformation Under Intense Shock Pressure Loading, Sandia National Laboratories Report No. SAND82-1317C, Albuquerque, NM, 5 pp., 1982. 

Fig. 3.4. Representative stress-particle velocity relations such as those shown in the relatively low shock-pressure region are used to determine impact stresses with good precision.

Impact velocities from about 2 to 6 kms which can produce shock pressures in the 110 GPa range, are routinely achieved with two-stage, light-gas guns. These systems are typically limited to diameters of from 12 to 25 mm. To achieve these velocities, propellant is used to accelerate a large piston which serves to compress a reservoir of helium or hydrogen gas to high pressure. The gas then accelerates the projectile over an acceleration distance of perhaps 25 m. 

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