Application of the Pegasus II Pulsed-Power Facility to the Study of Inertial Instability and Fracture of Cylindrical Tubes of Solid Aluminum

Understanding the surface stability of metals undergoing dynamic fracture at shock breakout is important to several applications in metals processing. The advantages of using the Pegasus II facility to investigate the phenomena occurring at shock break out are described. As an example of the data collected, we concentrate on brief descriptions of two experiments that compared the tensile failure, i.e. ''spall'', patterns in the presence of sinusoidal perturbations seeded on the free inner surface of cylindrical samples of 3 types of Al. These samples were composed variously of soft Al 1100-O, structural grade Al 6061-T6, and ultra-pure 99.99% Al and were subjected to Taylor waves with shock pressures of 14 GPa. We show that the material behind the exiting surface undergoes a type of failure termed here ''microspall'', resulting in the production of a significant volume of low-density, probably granular, material. The failure mechanism, combined with the forces that cause inertial instability, leads to rapid pattern growth in the failed material and subsequent pattern growth on the surface. Pattern growth was studied as a function of perturbation wavelength and amplitude. The different Al samples vary by an order of magnitude in yield strength, and some increase in pattern instability wasmore » observed at lower yield strength. The ultra-pure Al has exceptionally large grain size, in the mm range. No appreciable variation of spall pattern was observed due to grain size.« less