Spallation strength of single crystal and polycrystalline copper

Abstract
The spallation strength of single crystal copper foils 100 micrometers thick of the <110> and <100> orientations and of polycrystalline copper foils has been determined. Laser driving was used to launch miniature plates. Also, the spallation strength of polycrystalline copper was measured using conventional gas gun techniques and plates for comparison. Experimental measurements include VISAR records of the free surface particle velocity and micrographs of recovered flyers. A 1D hydrocode was used to simulate the VISAR records to determine the dynamic pressure history of the spallation process. Judging by the calculated pressures, it was found that the <110> foils were somewhat stronger than the <100> foils, which were about twice as strong as the polycrystalline foils. These were, in turn, substantially stronger than the larger sample plates (1.5 mm thick) of the gas gun. In the polycrystalline foils, small voids are found in recovered samples impacted at flyer plate velocities almost producing spallation in the gas gun, indicating that this sparse damage in the foils is able to grow substantially more in the much larger gas gun plates and under much slower gas gun loading.