Using Plate-Impact-Driven Ring Expansion Tests (Pidret) to Assess Analytical Models

When a cased explosive charge detonates, its metallic envelop is radially accelerated under the effect of the detonation products expansion. Numerous necks then appear leading to multiple fragmentation. Ejection velocities may reach values of about 2 km/s, which generates high kinetic energy debris. In industrial and military applications, the spatial distribution of the fragments and their statistics in terms of number, mass, and velocity are required to estimate safety or lethality areas. Since the pioneering works of Mott, numerous experimental, theoretical and numerical studies have been issued on the fragmentation of cased charges or simplified configurations such as hemispheres, cones, cylinders or rings. The present authors recently contributed to this topic by designing an original plate-impact-driven ring expansion test (PIDRET) set-up that is able to reliably expand thin metallic rings at strain rates close to 104 s-1 and follow their expansion thanks to synchronized photonic Doppler velocimetry (PDV) probes and ultra-high-speed cameras. These in-situ real-time observations, complemented by post-mortem observations, provide new insights into the high-strain rate expansion and fragmentation of various metals and alloys including steel, aluminum and copper. The number of visible necks and fragments are compared to the estimates obtained from analytical approaches such as linear stability analysis (LSA) and Grady and Olsen statistics-based model. Moreover, numerical simulations of the whole experimental set-up are carried out for designing experiments with various ring geometries in view of extending the range of the comparison with the above-mentioned analytical models.