Characterizations of Mg-W System Graded-Density Impactors for Complex Loading Experiments

We designed an Mg-W functionally graded-density materials system with two different sequences of density–thickness distributions and fabricated disk-like pellets with the graded-density materials by elaborate stacking of different metal powder layers, followed by a one-step hot-pressure sintering process. The microstructures of the sintered pellets were characterized using a scanning electronic microscope and a scanning acoustic microscope. The pellets were used as graded-density impactors (GDIs) to test their capabilities to produce complex particle-velocity wave profiles along a specified thermodynamic path. The wave profile was obtained from reverse-impact experiments using a two-stage light gas gun in which the GDI flyer impacted a lithium fluoride window. The particle-velocity history at the impact surface of the LiF window was deduced from the interference fringe numbers of the distance interferometer system for any reflector records. For GDIs consisting of nine composition layers of graded-density materials, the particle velocity profiles displayed combined shock loading and quasi-isentropic compressing and release processes. The impactor, consisting of 12 composition layers, produced wave profiles that contained shock loading, quasi-isentropic reloading, controlled releasing, and recompressing and released processes. The wave profiles simulated using a hydrodynamic computer model developed in house agree well with the experimental results as well as other theoretical results.