Based upon a study of the independent variation of peak pressure and pulse duration upon the shock loading response of OFE copper, the following conclusions can be drawn: (1) Increasing peak pressure or pulse duration was found to decrease the observed dislocation cell size and increase the yield strength and (2) the influence of pulse duration is attributed to the influence of reorganization time on the amount of dislocation generation during the rarefaction release.
The papers collected together in this volume constitute a review of recent research on the response of condensed matter to dynamic high pressures and temperatures. Inlcuded are sections on equations of state, phase transitions, material properties, explosive behavior, measurement techniques, and optical and laser studies. Recent developments in this area such as studies of impact and penetration phenomenology, the development of materials, especially ceramics and molecular dynamics and Monte Carlo simulations are also covered. These latest advances, in addition to the many other results and topics covered by the authors, serve to make this volume the most authoritative source for the shock wave physics community.
This book presents a set of basic understandings of the behavior and response of solids to propagating shock waves. The propagation of shock waves in a solid body is accompanied by large compressions, decompression, and shear. Thus, the shear strength of solids and any inelastic response due to shock wave propagation is of the utmost importance. Furthermore, shock compres sion of solids is always accompanied by heating, and the rise of local tempera ture which may be due to both compression and dissipation. For many solids, under a certain range of impact pressures, a two-wave structure arises such that the first wave, called the elastic prescursor, travels with the speed of sound; and the second wave, called a plastic shock wave, travels at a slower speed. Shock-wave loading of solids is normally accomplished by either projectile impact, such as produced by guns or by explosives. The shock heating and compression of solids covers a wide range of temperatures and densities. For example, the temperature may be as high as a few electron volts (1 eV = 11,500 K) for very strong shocks and the densification may be as high as four times the normal density.
Shock recovery experiments on copper have been conducted to investigate the influence of loading rate and stress amplitude on defect storage and post-shock mechanical properties. The shock risetimes varied approximately from one nanosecond for the shock experiments to one microsecond for quasi-isentropic loading experiments. All the experiments had the same peak pressure and pulse duration. Decreasing the strain-rate of loading is shown to increase both the defect storage and post-shock yield strength of copper. The effect of loading rate on post-shock substructure and mechanical response of impacted copper is postulated to be directly related to the amount of dislocation motion before interaction with other dislocations and to the amount of reversible dislocation motion and resultant annihilation during the rarefaction portion of the shock-release cycle. 10 refs., 5 figs.
The inelastic response and residual mechanical properties acquired from most shock compressed solids are quite different from those acquired from quasi-static or moderate strain rates. For instance, the residual hardness of many shock compressed metals has been found to be considerably lower than those loaded under quasi-static conditions to the same maximum stress. However, the residual hardness of shock compressed metals is much higher than those loaded quasi-statically to the same total strain. These observations suggest that the deformation mechanisms active during inelastic deformation under shock compression and quasi-static or moderate rates may be quite different. Therefore, the primary objective of this short book is to offer the reader a concise introduction on the Structure-Property Relationships concerning shock compressed metals and metallic alloys via shock recovery experiments. The first phase of the book, chapters 1 through 3 provides a brief historical perspective on the structure-property relationships as it pertains to shock compression science, then plastic deformation in shock compressed metals and metallic alloys is described in terms of deformation slip, deformation twinning, and their consequences to spall failure. Existing knowledge gaps and limitations on shock recovery experiments are also discussed. The fundamentals of shock wave propagation in condensed media are presented through the formation and stability of shock waves, then how they are treated using the Rankine-Hugoniot jump relations derived from the conservation of mass, momentum, and energy. The equation of states which govern the thermodynamic transition of a material from the unshock state to the shock state is briefly described and the elastic-plastic behavior of shock compressed solids is presented at the back end of the first phase of this book. The second phase of the book describes the geometry and design of shock recovery experiments using explosives, gas and powder guns. Then results derived from the residual mechanical properties, microstructure changes, and spall failure mechanisms in shock compressed metals and metallic alloys with FCC, BCC, and HCP crystal lattice structures are presented. Also, results on the residual microstructure of explosively compacted powders and powder mixtures are presented. Lastly, the book closes with the new frontiers in shock recovery experiments based on novel materials, novel microscopes, novel mechanical processing techniques, and novel time-resolved in-situ XRD shock experiments.
