Shock-loaded copper

Figure 6.1. Stress-strain behavior of shock-loaded copper compared to the annealed starting condition illustrating an enhanced flow stress following shock-wave deformation compared to quasi-static deformation (based on an equivalent strain basis).

To illustrate the effect of radial release interactions on the structure/ property relationships in shock-loaded materials, experiments were conducted on copper shock loaded using several shock-recovery designs that yielded differences in es but all having been subjected to a 10 GPa, 1 fis pulse duration, shock process [13]. Compression specimens were sectioned from these soft recovery samples to measure the reload yield behavior, and examined in the transmission electron microscope (TEM) to study the substructure evolution. The substructure and yield strength of the bulk shock-loaded copper samples were found to depend on the amount of e, in the shock-recovered sample at a constant peak pressure and pulse duration. In Fig. 6.8 the quasi-static reload yield strength of the 10 GPa shock-loaded copper is observed to increase with increasing residual sample strain. 

Figure 6.8. Plot of the quasi-static reloaded yield stress of shock-loaded copper versus the natural logarithm of residual strain for a 10 GPa symmetric shock with 1 /is pulse duration.

Figure 6.9. TEM micrographs of shock-loaded copper as a function of (a) <2%...

Figure 6.14 shows the reload compressive stress-strain response of shock-loaded copper as a function of pulse duration [40]. For copper shock loaded to 10 GPa the yield strength is observed to increase with increasing pulse... 

G.T. Gray III, P.S. Follansbee, and C.E. Frantz, Effect of Residual Strain on the Substucture Development and Mechanical Response of Shock-Loaded Copper, Mater. Sci. Engrg. AIII (1989), 9. 

G.T. Gray III, The Effect of Residual Strain on Twinning in Shock-Loaded Copper, in Proc. 44th Annual Meeting of Electron Microscopy Soc. (edited by G.W. Bailey), San Francisco Press, 1986, 422 pp. 

G.T. Gray III and P.S. Follansbee, Influence of Peak Pressure and Pulse Duration on the Substructure Development and Threshold Stress Measurements in Shock-loaded Copper, in Impact Loading and Dynamic Behavior of Materials (edited by C.Y. Chiem, H.-D. Kunze, and L.W. Meyer), Deutsche Gesellschaft fuer Metall-kunde, Germany, 1988, 541 pp. 

G.T. Gray III and C.E. Morris, Influence of Loading Rate of the Mechanical Response and Substructure Evolution of Shock-Loaded Copper, in DYMAT 91, Journal De Physique IV, Colloque C3, Suppl. an Journal de Physique III, Vol. 1 (1991), C3-191. 

Gray and Follansbee [44] quasi-statically tested OFE copper samples that had been shock loaded to 10 GPa and pulse durations of 0.1 fis, 1 /rs, and 2 fus. The quasi-static stress-strain curves are shown in Fig. 7.10 with the response of annealed starting copper included for comparison. The yield strength of shock-loaded copper is observed to increase with pulse duration, as the work-hardening rate is seen to systematically decrease. 

Rosenberg, Z., and Partom, Y. (1984), Direct Measurement of Temperature in Shock Loaded Polymethlmetacrylate with Very Thin Copper Thermisters, in Shock... 

Figure 6.14. Stress-strain response of copper shock loaded to 10 GPa as a function of duration.

Appleton and Waddington [40] present experimental evidence that pulse duration also affects residual strength in OFHC copper. Samples shock loaded to 5 GPa for 1.2 ps pulse duration exhibit poorly developed dislocation cell structure with easily resolvable individual dislocations. When the pulse duration is increased to 2.2 ps (still at 5 GPa peak stress) recovered samples show an increase in Vickers hardness [41] and postshock electron micrographs show a well-developed cell structure more like samples shock loaded to 10 GPa (1.2 ps). In the following paragraphs we give several additional examples of how pulse duration affects material hardness. 

Materials. At these extremely low temperatures, ferrous metals become brittle and consequently cannot resist shock loads. In a cryogenic pump, elements having a low transition from the ductile to the brittle state, must be used. Such elements are aluminum, copper, silver, lead, nickel, and beryllium. 

While high defect generation rates in the shock can qualitatively be applied to explain the approximately sevenfold yield increase in copper to 210 MPa following loading to a 10 GPa shock [13], significant shock har-... 

The shock-induced micromechanical response of <100>-loaded single crystal copper is investigated [18] for values of (WohL) from 0 to 10. The latter value results in W 10 Wg at y = 0.01. No distinction is made between total and mobile dislocation densities. These calculations show that rapid dislocation multiplication behind the elastic shock front results in a decrease in longitudinal stress, which is communicated to the shock front by nonlinear elastic effects [pc,/po > V, (7.20)]. While this is an important result, later recovery experiments by Vorthman and Duvall [19] show that shock compression does not result in a significant increase in residual dislocation density in LiF. Hence, the micromechanical interpretation of precursor decay provided by Herrmann et al. [18] remains unresolved with existing recovery experiments. 

It should be observed that every element except the powder system in the recovery system is chosen for favorable shock properties which can be confidently simulated numerically. The precise sample assembly procedures assure that the conditions calculated in the numerical simulations are actually achieved in the experiments. The influence of various powder compacts in influencing the shock pressure and mean-bulk temperature must be determined in computer experiments in which various material descriptions are used. Fortunately, the large porosity (densities from 35% to 75% of solid density) leads to a great simplification in that the various porous samples respond in the same manner due to the radial loading introduced from the porous inclusion in the copper capsule. 

SAFETY PRECAUTIONS - Very stable, but should be made up as needed. AN should be kept dry to ensure proper detonation. This explosive is a definite fire hazard. Flame and heat should be avoided. Not shock sensitive as explosives go, but can be detonated by a very sharp blow (30cm drop of a 2 Kg. weight will detonate). Copper and brass should be avoided in manufacture and all munitions loading and finished products. 

Calculated results on shock wave loading of different inert barriers in a wide range of their dynamic properties under explosion on their surfaces of concrete size charges of different explosive materials in various initial states were obtained with the use of the one-dimensional computer hydrocode EP. Barriers due to materials such as polystyrene, textolite, magnesium, aluminum, zinc, copper, tantalum or tungsten were examined (Fig. 9.35). Initial values of pressure and other parameters of loading on the interface explosive-barrier were determined in the process of conducted calculations. Phenomena of propagation and attenuation of shock waves in barrier materials were considered too for all possible situations. 

Properties Yellow to red crystals or granules. Does not melt on heating but explodes when heated to 300°. It must be loaded in projectiles by pressing or tamping. Ammonium picrate absorbs moisture and in wet condition reacts slowly with metals, particularly copper and lead, to form picrates which are sensitive and dangerous. Its explosive strength is inferior to that of TNT, but it is very valuable because of its extreme resistance to impact, shock, and friction. It is not detonated by fulminate. Commonly used with a booster of picric acid or Tetryl. Rate of detonation 6500 m/sec. (d = 1.45). 

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