Shock history

The structure/property relationships in materials subjected to shock-wave deformation is physically very difficult to conduct and complex to interpret due to the dynamic nature of the shock process and the very short time of the test. Due to these imposed constraints, most real-time shock-process measurements are limited to studying the interactions of the transmitted waves arrival at the free surface. To augment these in situ wave-profile measurements, shock-recovery techniques were developed in the late 1950s to assess experimentally the residual effects of shock-wave compression on materials. The object of soft-recovery experiments is to examine the terminal structure/property relationships of a material that has been subjected to a known uniaxial shock history, then returned to an ambient pressure... 

For F and FF chondrites, the isotopic data do not correlate as well with the petrologic type as they do for H chondrites. This could reflect earlier disruption of the parent asteroids or the subsequent shock history or both. In general, the ages of the L chondrites tend to be younger than for the H group, but the overall timescales are similar for H, L, and LL chondrites. 

Haack H., Scott E. R. D., and Rasmussen K. L. (1996) Thermal and shock history of mesosiderites and their large parent asteroid. Geochim. Cosmochim. Acta 60, 2609-2619. 

Ostertag R., Stoffler D., Bischoff A., Palme H., Schultz L., Spettel B., Weber H., Weekwerth G., and Wanke H. (1986) Lunar Meteorite Yamato-791197 Petrography, shock history and chemical composition. Mem. Natl. Inst. Polar. Res. (Tokyo), Spec. Issue 41, 17-44. 

As alluded to above in the discussion of absolute ages of differentiated objects, the eucrites have suffered a more prolonged and complex thermal and shock history, which is reflected in their internal Mn- Cr systematics. Despite this, excesses of Cr in bulk samples of eucrites are well correlated with Mn/Cr (Figure 5) indicating large-scale differentiation on the eucrite parent body prior to the decay of Mn (Lugmair and Shukolyukov, 1998). The slope of the correlation line yields Mn/ Mn = (4.7 0.5) X 10 which is nearly two half-lives of Mn steeper (older) than the 1.25 X 10 value obtained for angrites. Thus, these data indicate that the parent asteroid of the eucrites (Vesta ) was... 

Emsley, John (2000). The Shocking History of Phosphorus. A Biography of the Devil s Element. London, U.K. Macmillan. 

Three pianes or two dimensionai piots are used to describe the shock properties and shock histories of materiais. They are the distance-time (x-t) piane, the pressure-particie veiocity piane (P-u) described by equation 4-10, and the pressure-specific voiume (P-vs) curve. 

Now that it is possible to establish test facilities in a laboratory to simulate the time history of an earthquake seismic tests are conducted by creating the ground movements in the test object. Other methods, such as by analysis or by combined analysis and testing, are also available. Refer to IEEE 344 and lEC 60980 for more details. For this purpose a shake table, able to simulate the required seismic conditions (RRS) is developed on which the test object is mounted and its performance observed under the required shock conditions. Since it is not easy to create such conditions in a laboratory, there are only a few of these facilities available. The better equipped laboratories are in Japan, the USA, the UK, Greece, Germany, India and China. In India the Earthquake Engineering Department (EQD) of the University of Roorkee (UoR) is equipped with these facilities. 

Another way of representing shock-wave profiles is in the form of F-t histories of the pressure or another variable at a series of points along its direction of propagation, as in Fig. 2.9. In the above example, the leading part of the shock front arrives first, effectively increasing the pressure instantaneously. The rarefaction arrives later and decreases the pressure over a time... 

It is important to note that the state determined by this analysis refers only to the pressure (or normal stress) and particle velocity. The material on either side of the point at which the shock waves collide reach the same pressure-particle velocity state, but other variables may be different from one side to the other. The material on the left-hand side experienced a different loading history than that on the right-hand side. In this example the material on the left-hand side would have a lower final temperature, because the first shock wave was smaller. Such a discontinuity of a variable, other than P or u that arises from a shock wave interaction within a material, is called a contact discontinuity. Contact discontinuities are frequently encountered in the context of inelastic behavior, which will be discussed in Chapter 5. 

Of all the piezoelectric crystals that are available for use as shock-wave transducers, the two that have received the most attention are x-cut quartz and lithium-niobate crystals (Graham and Reed, 1978). They are the most accurately characterized stress-wave transducers available for stresses up to 4 GPa and 1.8 GPa, respectively, and they are widely used within their stress ranges. They are relatively simple, accurate gauges which require a minimum of data analysis to arrive at the observed pressure history. They are used in a thick gauge mode, in which the shock wave coming through the specimen is... 

The diagnostics applied to shock experiments can be characterized as either prompt or delayed. Prompt instrumentation measures shock velocity, particle velocity, stress history, or temperature during the initial few shock transits of the specimen, and leads to the basic equation of state information on the specimen material. Delayed instrumentation includes optical photography and flash X-rays of shock-compression events, as well as post-mortem examinations of shock-produced craters and soft-recovered debris material. 

Table 3.3 summarizes the history of the development of wave-profile measurement devices as they have developed since the early period. The devices are categorized in terms of the kinetic or kinematic parameter actually measured. From the table it should be noted that the earliest devices provided measurements of displacement versus time in either a discrete or continuous mode. The data from such measurements require differentiation to relate them to shock-conservation relations, and, unless constant pressures or particle velocities are involved, considerable accuracy can be lost in data processing. 

Over the 40-yr history of shock-compression science, numerous physical phenomena have been considered for use in detecting wave profiles. Few of the devices have actually been used for a significant and persistent study. Part of this history is connected to the difficulty in actually developing a credible... 

In order to anticipate problems and to interpret observations under the extreme conditions of shock compression, it is necessary to consider structural and electronic characteristics of PVDF. Although the phenomenological piezoelectric properties of PVDF are similar to those of the piezoelectric crystals, the structure of the materials is far more complex due to its ferroelectric nature and a heterogeneous mixture of crystalline and amorphous phases which are strongly dependent on mechanical and electrical history. 

It is known that mechanical and physical properties of the amorphous and crystalline phases differ significantly [80T01]. For this reason, it is anticipated that properties of the mechanically and electrically treated film will depend explicitly on its history. Shock-compression measurements such as those carried out on amorphous materials in a thick form [80M01] will not prove characteristic of thin, treated films. 

The plan of this chapter is first to briefly recall the history of work in solid state chemistry. Following this, the mechanisms that the author proposes control shock-induced solid state chemistry will be considered in terms of shock-induced changes to potential reactants. Enhancements in solid state chemical reactivity are considered in Chap. 7. There are many groups who... 

Fig. 8.3. The yield of shock-synthesized zinc ferrite is found to be strongly dependent on the early loading history. This characteristic is thought to be an indication of shock modification on subsequent chemical reaction.

---