Shock conditions

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. 

For shock-synthesis and processing experiments, less precise systems are typically employed. These systems use commercial explosives that may be used to accelerate plates or to compress samples in the form of a tube. These systems are suitable for establishing nominal shock conditions for materials processing experiments, but are generally not suitable for careful characterization of materials response [87G02, 88M01]. 

Fig. 5.25. The shock temperature in LiCl KCl electrolytes is controlled with the use of eleetrolytes with initial densities as shown. The cirele represents the shock conditions. Upon release of pressure the final temperature is expected to cross the melt eurve for certain initial conditions.

Fig. 7.7. Studies of the catalytic activity of shock-modified rutile in the oxidation of CO shows greatly enhanced catalytic activity, which is strongly influenced by the shock conditions [86G01].

Shock-synthesis experiments were carried out over a range of peak shock pressures and a range of mean-bulk temperatures. The shock conditions are summarized in Fig. 8.1, in which a marker is indicated at each pressure-temperature pair at which an experiment has been conducted with the Sandia shock-recovery system. In each case the driving explosive is indicated, as the initial incident pressure depends upon explosive. It should be observed that pressures were varied from 7.5 to 27 GPa with the use of different fixtures and different driving explosives. Mean-bulk temperatures were varied from 50 to 700 °C with the use of powder compact densities of from 35% to 65% of solid density. In furnace-synthesis experiments, reaction is incipient at about 550 °C. The melt temperatures of zinc oxide and hematite are >1800 and 1.565 °C, respectively. Under high pressure conditions, it is expected that the melt temperatures will substantially Increase. Thus, the shock conditions are not expected to result in reactant melting phenomena, but overlap the furnace synthesis conditions. 

Four different material probes were used to characterize the shock-treated and shock-synthesized products. Of these, magnetization provided the most sensitive measure of yield, while x-ray diffraction provided the most explicit structural data. Mossbauer spectroscopy provided direct critical atomic level data, whereas transmission electron microscopy provided key information on shock-modified, but unreacted reactant mixtures. The results of determinations of product yield and identification of product are summarized in Fig. 8.2. What is shown in the figure is the location of pressure, mean-bulk temperature locations at which synthesis experiments were carried out. Beside each point are the measures of product yield as determined from the three probes. The yields vary from 1% to 75 % depending on the shock conditions. From a structural point of view a surprising result is that the product composition is apparently not changed with various shock conditions. The same product is apparently obtained under all conditions only the yield is changed. 

The response of titanium-aluminum powder mixtures in a 3 1 molar ratio was investigated under the same shock-loading conditions as in the nickel aluminides. Such mixtures are especially interesting in that the shock impedances of the materials are approximately equal and both are relatively hard and difficult to deform. In addition to any chemical differences, such materials should prove to be difficult to mix with the shock conditions. 

Fig. 8.8. The influence of starting material ratio on shock conditioning has been investigated for coarse powders in ratios of nickel to aluminum of 3 1, 2 1, and 1 1. The data show a strong influence of the ratio of the potential reactants consistent with the concept of mechanical mixing. [91D01],...

Fig. 8.9. The strongly exothermic reaction of hematite and aluminum mixtures shows effects strongly dependent on shock conditions that vary from no reaction to a strong, vigorous reaction. The observed behavior indicates that the heat of reaction does not play a dominant role in initiation of reaction.

Unstable liquid A liquid that, in its pure state or as commercially produced, will react vigorously in some hazardous way under shock conditions (i.e., dropping), certain temperatures, or pressures. 

FIGURE 8.3 Comparison of measured and calculated NO concentration profiles for a CH4—02—N2 mixture behind reflected shocks. Initial post-shock conditions r= 2960K, P = 3.2 atm (from Bowman [12]). 

This self-sustained balance of reciprocal activation and suppression of Tregs and MO may be important for maintenance of peripheral tolerance in healthy individuals. However, this balance can be impaired during infection and inflammation. Under septic shock conditions, increased Treg numbers can be seen in patients, which interfere with MO survival that ultimately leads to aggravation of the septic shock. 

Where high shock conditions are likely to be encountered, some provision must be made to further secure the lead in place by supplementing the side wall friction obtd during consolidation. Scoring of the wall of the lead hole (See Fig l-70b) is the usual practice. It can be accomplished by tapping the hole and then passing a drill thru to remove the crests of the threads, unless very fine threads are used. This smoothes the roughness of... 

Shock is a clinical syndrome in which profound and widespread reduction in the effective delivery of oxygen and other nutrients to the tissues. In shock condition, the individual is weak, anxious with coldness of extremeties, sweeting and marked fall in arterial pressure. Physiologic mechanisms can effect the arterial pressure by acting on one or more of two variables i.e. preload, impedance to blood flow (after load) and myocardral contractility. These macha-nisms include ... 

The structure of trauma injuries is given in Table 20.1. There were on average 1.5 injuries per injured person. The most common localization of injuries was in the lower limbs - 59.4%, of which shin - 47.4%, upper limbs and head - 25.0% each. The injuries with high lethality included injuries of the chest and abdominal cavities, and also pelvis, which were accompanied by a deep shock condition. 

The plots show that under cold shock and for all values of Bi, the maximum tensile stress is achieved at the surfaces while the maximum compressive stress is achieved at the centre of the plate. The opposite is true for hot shock conditions. The maximum tensile stress, cr, achieved at the surface during cold shock and at the centre during hot shock, is then plotted against IIBi, as shown in Fig. 15.3. 

This section aims to present briefly the experimental methods used to evaluate the performance of ceramics and CMCs under conditions of thermal shock. Reference is made to techniques used to impose the actual thermal shock condition as well as the destructive and non-destructive methods employed to assess damage morphologies and changes in residual properties. 

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