Principal Hugoniot, Second-Shock Hugoniot, and Release Behavior of Pressed Copper Powder

Abstract

Principal Hugoniot, second-shock Hugoniot, and adiabatic release data obtained by gas gun experimental techniques are presented for porous copper prepared by hydrostatically pressing copper powder to a density of about 6.4 g/cm 3 • The bulk of the data presented pertain to a powder with initial particle diameters of 30 p., however, sufficient data are also presented for other particle diameters of 10, 50, and 100 p. to show that particle size variations over this range have no distinct effect on shock loading properties. Transmitted wave profiles for each of these materials are characterized by a single precursor wave (amplitude ",,1.4 kbar, velocity "'1.9 mm/p.sec) followed by a main shock wave. Principal Hugoniot data for stress levels above the precursor amplitude and over the entire stress range examined (up to ",35 kbar) are well represented by the rel~tion a2= 1 + (ai-I) eXPL -a(P2-PI)], where a2 is the distention ratio (density of solid copper/density of porous copper) at the stress level P2, PI is the precursor amplitude, al is the value of a at PI, and a is an adjustable parameter (found to be 0.254 kbac 1 ). Second-shock Hugoniot data (i.e., for a Hugoniot centered at a prestressed state P2, (2) are also well represented by the above equation provided al and PI are changed to correspond to the prestressed state. Release data indicate that the shock loaded porous copper unloads along a path that is essentially the same as the loading path. These data, however, extend only over the upper one-fourth of the stress range between the shock loaded state and the foot of the release adiabat and a straight-line continuation of the measured adiabat indicates that the compression process is not reversible.

Effect of Strength and Plasticity of the Material and Particle Size of a Porous Medium on Shock-Wave Deformation

“…This agrees with the conclusions drawn by Kiselev [8]: the width of the compression-wave front in a porous material is determined by the time needed to fill the pores; the greater the characteristic size of pores or grains, the greater this time. Note, a similar structure consisting of two compression waves was observed, e.g., in studying dynamic compression of porous aluminum [8] and pressed copper powder samples [10] with a porosity k ≈ 1.2-1.5 and close velocities of the impactor. With increasing loading intensity, the second wave catches up with the first wave, the W (t) profiles are transformed, and the two-wave configuration is no longer observed for W 0 ≈ 300 m/sec.…”

“…In addition to these features, sintered powders, foam-based materials, and ceramics whose particles are connected by a skeleton have additional peculiarities caused by skeleton compression or breakdown. For this reason, the behavior of a porous or fragmented material under shock-wave compression can be characterized by propagation of complicated multi-wave structures consisting of one or several elastic precursors and a wave of irreversible compression [5][6][7][8][9][10]. If the particles of a porous medium are connected by a skeleton, a three-wave configuration propagates over such a medium [5][6][7]9].…”

“…The first wave is elastic, the second wave is generated by skeleton breakdown, and the third wave is caused by splitting of fragments and a decrease in the degree of their anisotropy, i.e., is a wave of irreversible compression. If the particles of a porous medium are not connected by a skeleton, a two-wave configuration propagates in such a medium [8,10]. We will call it a fragmented medium.…”

Particle morphology and packing effects on the shock loading of powders

“…The basic details are given elsewhere (Petrie and Page 1991;Petrie 1991) but the principal features and some extensions are described below. As shown by Boade (1970), there is a precursor wave generated in unsintered powder and twin precursor waves in sintered powder when these are subjected to shock loading. Only the case of a single precursor will be considered here.…”

The influence of particle morphology on the dynamic densification of metal powders

“…The extent and distance over which these waves can be attenuated are important properties for shock mitigation, and rely upon understanding the behavior of powders under strong and weak loading. While earlier studies have shown the high stress behavior of porous materials to be insensitive to powder configuration [1], prior work on metal powder mixtures demonstrated that both powder morphology and particle size play a strong role in densification at low stresses [2,3].…”