Gas gun driven dynamic expansion of 3D-printed rings

This experimental campaign presents a new experimental setup to study dynamic fragmentation of metallic rings manufactured by 3D-printing technology. The ring is inserted over a ductile thin-walled tube which is impacted axially by a conical nosed cylindrical projectile fired by a single-stage light-gas gun. The diameter of the projectile is larger than the internal diameter of the thin-walled tube, which expands as the projectile advances, pushing radially outwards the metallic ring, that eventually breaks into multiple fragments. The impact velocities considered in the present experimental campaign range from 200 m/s to 400 m/s. The ring specimens are printed by Selective Laser Melting technique, with an inner diameter of 14 mm and square cross section of 2 × 2 mm2. Three materials have been tested: Aluminium (ALSi10Mg), Titanium (Ti6Al4V), and Inconel (IN718). To obtain time-resolved information on the mechanics of fragmentation, the number of fractures, and the size of the fragments, the tests have been recorded with two-high speed cameras. A tunnel-shaped soft casing made of polymer foam is placed around the specimen to softly recover the ejected fragments, that have been weighted and sized to determine the statistics of the fragments size distribution. In addition, the predictions of the fragmentation theory of Kipp and Grady, and the stability analysis approach of Molinari and co-workers for the evolution of the number of fragments with the impact velocity have been compared with the experimental results. Excellent qualitative agreement has been found within the whole range of loading rates investigated with Kipp and Grady’s theory. Compared to other available techniques for dynamic fragmentation of rings, in which the expansion of the specimen is driven by electromagnetic or explosive loading, this experimental setup stands out for its simplicity, fast operation, and quick assembly, which facilitates performing extensive experimental campaigns.