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

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/cm3. The bulk of the data presented pertain to a powder with initial particle diameters of 30μ, however, sufficient data are also presented for other particle diameters of 10, 50, and 100μ 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/μsec) 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 relation α2=1 + (α1−1) exp[−â(P2−P1)], where α2 is the distention ratio (density of solid copper/density of porous copper) at the stress level P2, P1 is the precursor amplitude, α1 is the value of α at P1, and â is an adjustable parameter (found to be 0.254 kbar−1). Second-shock Hugoniot data (i.e., for a Hugoniot centered at a prestressed state P2, α2) are also well represented by the above equation provided α1 and P1 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.